Emission Systems – Worth Tinkering?

Why You Shouldn’t Support Mandatory Vaccinations 

Last Updated 22/07/2019

There’s a growing trend of modifying, bypassing or deleting engine emission controls in modern vehicles. Claimed benefits include improved performance, improved fuel economy, improved engine life and even environmental benefits. Is any of it true? Should you consider tinkering with your vehicle’s emission controls? This article hopefully provides some information to help make a decision.

Sources of Information

Even with no technical understanding of emissions control, you should understand and appreciate the following:

  • People who sell stuff related to modifying or bypassing emission controls are trying to make money. They have a conflict of interest. They are not a source of accurate information.
  • People who tinker are sometimes addicted to tinkering. They’re constantly on the lookout for the next thing to play with. They’ll always report benefits from their tinkering, even if there are no benefits, because they need to validate their efforts.
  • Some people are addicted to spending money on modifications. They spend money modifying everything. They’ll always report benefits from their modifications, even if there are no benefits, because they need to validate their spending.
  • Some people are addicted to the perceived status they receive from modifying their car. They proudly list out all their modifications in the footer of every communication they make, and people in their community give them respect for having such a long list of modifications. They will always support more modifications because it is consistent with their addiction for more status.
  • Some people obviously don’t try for even 5 minutes to understand something and instead just make some shit up in their head and spew it out on a forum.
  • Experiments determining the benefits of modifying or bypassing emission controls are flawed. They suffer from poor experimental method, poor control of variables and poor measurement of results. The people doing the experiments often have an agenda and / or suffer from confirmation bias and placebo.

So you need to be weary of what you read. There’s a lot of crap information out there.

Overall Engine Tuning

Often you’ll read something along the lines of:

“Modern engines are tuned around emissions. Therefore power, economy and engine longevity must suffer.”

Is this accurate? Lets look at the key engine emissions and how they relate to power, economy and engine longevity. This section is related to engine tuning itself and not related to external emission systems that clean up the exhaust after the process in the engine is complete.

Firstly, in general, using less fuel reduces all emissions, since even if you keep the emissions in the same concentrations, less in total will be produced if you burn less fuel. So improving fuel economy helps to reduce emissions. Of course there will be some compromises between emissions and economy when looking into finer details, but broadly speaking less fuel consumption = less emissions.

Hydrocarbons are the result of incomplete combustion. They cause smog, liver disease, lung disease and cancer. Hydrocarbon emissions are reduced by ensuring all the fuel is fully burnt. This means reducing hydrocarbon emissions also improves fuel efficiency and power output for a given quantity of fuel injected into the engine. There is no significant impact to engine longevity when reducing hydrocarbon emissions.

Carbon Monoxide is a product of incomplete combustion. It disrupts oxygen delivery in blood, increases the risk of heart disease and reacts with air to produce smog. Carbon monoxide emissions are reduced by ensuring all the fuel is fully burnt. This means reducing carbon monoxide emissions also improves fuel efficiency and power output for a given quantity of fuel injected into the engine. There is no significant impact to engine longevity when reducing hydrocarbon emissions.

Soot is the result of incomplete combustion. It causes lung disease, cancer and cardiovascular disease. Soot emissions are reduced by ensuring all the fuel is fully burnt. This means reducing soot emissions also improves fuel efficiency and power output for a given quantity of fuel injected into the engine. Reducing soot also improves engine longevity since soot is abrasive and causes wear, although any improvement in engine life from stricter soot emissions is not likely to be significant.

Carbon Dioxide is non-toxic at low levels but is an asphyxiant at higher concentrations. Carbon dioxide concentrations in the atmosphere are not going to reach asphyxiant levels through burning fossil fuels. The problem with carbon dioxide is that it contributes to global warming and thus is becoming an increasingly important emission. Carbon dioxide emissions are directly proportional to how much fuel is burnt. This means reducing carbon dioxide emissions and improving fuel economy are the same thing. Reducing carbon dioxide emissions also improves engines longevity, since it means the engine is burning less fuel and doing less work. Reducing carbon dioxide emissions is becoming a higher priority in modern vehicles and therefore fuel economy is increasing in importance.

Nitrogen Oxides (NOx) are the result of high combustion temperatures. It causes smog, acid rain and lung disease. NOx emissions are reduced by using Exhaust Gas Recirculation (EGR) to reduce combustion temperature. Reduced combustion temperature improves engine longevity. There is a tradeoff between NOx emissions and soot which is explained in more detail in a separate section below. EGR improves fuel economy in petrol engines. EGR may negatively impact fuel economy in diesel engines and is also treated in a separate section below. NOx is also controlled through pilot injections and timing but is not something that can be easily modified with typical emission tinkering techniques and so is not treated in this article.

Limiting the maximum fuel injected into the engine helps to reduce all emissions. Less fuel means a more complete burn, less soot and less energy to create heat and NOx. Modern engines are tuned to limit fuel injection quantity to meet emission standards. The fuel injection quantity is optimised for the most complete combustion of fuel and maximum fuel efficiency.

This means you can dump more fuel into the engine to generate more power. The extra power is not due to improving efficiency or optimising combustion. The extra power is a result of a greater quantity of fuel injected into the engine. This reduces fuel efficiency, since the fuel burn will not be as complete. Emissions will also increase, as well as the associated environmental and health effects caused by those emissions. More fuel also increases wear in the engine through higher temperatures and pressures. Restricting injected fuel volume improves efficiency and improves engine life. Dumping more fuel reduces efficiency, increases emissions and reduces engine longevity. Another consequence of dumping more fuel is that your EGR valve, catalytic converter and diesel particulate filter will foul up faster due to the increased production of soot.

Performance chips work by dumping more fuel.

Exhaust Gas Recirculation (EGR)

I’ll open this section with two incredibly important points. So important that, even with no technical understanding of EGR, they immediately cast massive doubt over whether modifying or disabling the EGR provides any advantages at all.

  1. Some people who clean (unblock) their EGR system report improved performance and fuel economy. Some people who block, disable or restrict their EGR also report improved performance and fuel economy. You can verify this by reading forum posts on EGR cleaning and EGR blocking. According to these anecdotes, both blocking and unblocking the EGR system improves performance and fuel economy.
  2. Before EGR was introduced, a well looked after heavy duty truck engine was capable of doing in excess of 1,000,000km. After EGR was introduced, a well looked after heavy duty truck engine was still capable of doing +1,000,000km. Before EGR was introduced, a well looked after light duty car engine was capable of doing +500,000km. After EGR was introduced, a well looked after light duty car engine was still capable of doing over 500,000km. You can verify this through second hand high mileage cars and trucks that are advertised for sale.

To me, without even looking into any details, that’s job done. Clearly blocking and unblocking the EGR can’t simultaneously yield the same results. Point 1 tells me that blocking and unblocking the EGR makes less difference to performance and economy than what can be measured outside of the laboratory. Confirmation biasplacebo and poor experimental method are much more powerful factors in the reported results. Point 2 tells me that EGR doesn’t impact engine longevity significantly. There are much more significant factors that determine engine life.

Lets look at the EGR system in more detail to see if we can validate the conclusions in the paragraph above.

Partial Blockage of EGR does Nothing

In modern vehicles usually you cannot completely block or disable the EGR. If you do you may get the engine check light illuminated, possible activation of limp mode, rough running, difficulty starting, stalling, unpredictable intake pressure and erratic performance. So instead of completely blocking the EGR, tinkerers will partially restrict the EGR. A blanking plate with a hole in it is the most common solution.

The problem with this is that the EGR control system is a closed loop system. The EGR valve position is controlled to meet the required EGR flow rate. EGR flow is usually measured by the pressure differential across the EGR valve, or by comparing the measured intake flow rate with the expected intake flow rate and using the difference to calculate EGR flow.

When you restrict the EGR, the target EGR flow rate does not change. This means the EGR valve opens more to compensate for the restriction. All you’re doing is shifting the operating range of the EGR valve as depicted in the graph below. The quantity of exhaust gas being recirculated does not change.

EGR Valve

The EGR system is built to accommodate the accumulation of soot. When clean it can supply much more than the target flow rate so that, as it becomes restricted with soot, it can still meet target flow rate by opening the valve more. So what you are doing by adding a restriction is reducing the system’s capability of compensating for soot accumulation. You’ll need to clean out the EGR more frequently. Other than that there is no change to EGR flow and therefore no change to engine longevity, fuel economy and performance. Any reported benefits can be attributed to confirmation bias, placebo and poor experimental method.

What if you partially restrict the EGR to the extent that the control system is no longer able to meet target flow? Then you get an engine check light, possible limp mode, rough running, difficulty starting, stalling, unpredictable intake pressure and erratic performance.

EGR and Soot

There is a tradeoff between NOx emissions and soot emissions. For a given design, reducing NOx increases soot. Emission standards require simultaneous reduction of soot and NOx. This means that when EGR was introduced, despite the additional soot caused by EGR, the engine’s soot loading was less than prior to the introduction of EGR, since the design must simultaneously meet stricter NOx and soot emissions. The design and tuning of the EGR equipped engine generates far less soot to start with, but then the EGR bumps up the soot levels slightly whilst still complying with soot emission standards.

diesel soot

These old trucks pumped out plumes of soot yet they lasted forever. No one was complaining about soot causing premature wear back then, probably because the after market industry was not advanced enough to con people out of their money. Image: Wikipedia

Pre EGR, when there were less stringent NOx and soot emission standards, trucks billowed out a heap of thick black smoke. Those engines had a massive soot loading, yet they were able to last a million kilometers or more. Since then both NOx and soot emissions have been reduced. Fuel has also contributed to cleaner running engines, since the fuel has become cleaner through improved processing techniques and stricter standards. So, despite the fact that the EGR is present, the amount of soot generated in clean burning modern engines is much less than in old engines. If the old engine did not prematurely fail due to soot then it makes sense that a modern engine can also avoid premature failure due to soot. This is consistent with the fact that modern heavy duty truck engines can still last in excess of a million kilometers.

Not only are these modern engines inherently cleaner than old engines to meet soot emissions and improve fuel economy, they’re also designed to tolerate the soot of normal operation. They have oil filters to filter out the bigger stuff. The oil is designed with additives to keep the finer soot in suspension, prevent it from agglomerating, and prevent it from significantly impacting the lubricating performance of the oil. The top of the piston and the piston ring have been designed to accommodate normal levels of soot. Service intervals are determined to ensure the oil filter and the oil itself do not become overloaded with soot. So, despite EGR being the source of additional soot, the overall soot level is low enough and the design is such that the engine will not fail prematurely due to EGR. This is why truck engines can still last +1,000,000km and car engines can still last +500,000km. This tells us that EGR is not a source of significant wear, and that other factors determine how long an engine lasts. Yes, soot causes wear. Is EGR a significant source of wear? No.

An EGR restriction is not some magical engine life extender!

It’s interesting that the same people who claim EGR causes significant engine damage due to soot often also have a performance chip installed. Performance chips dump more fuel in the engine causing a rich mixture and a large increase in soot production. Also engine wear is increased due to increased combustion pressure and temperature. Do you think these guys are experts in extending engine life? Sounds to me like they’re addicted to throwing money at their vehicle and they need to validate their addiction.

Actually restricting EGR can reduce engine life through increased combustion temperatures, as well as through interfering with other design elements as you’ll see in the sections below. I don’t believe that EGR extends engine life overall. I believe there are many conflicting effects of EGR and overall it’s not a significant factor for engine life.

People report cleaner looking oil after they have blocked or restricted the EGR which they think is proof that blocking or restricting the EGR is good.

The performance of oil is not measured by simply looking at it!

Oil performance is measured in a laboratory. Provided oil is not overloaded with soot such that it is unable to keep the soot in suspension, soot doesn’t negatively impact the oil’s lubricating performance significantly. It’s purposely formulated this way. This is verified by oil analysis results reporting excellent lubricating performance of used engine oil, provided the oil is still within its recommended service life.

Here are my oil analysis results from my 2007 Diesel Toyota Hilux. The oil had done 10,000km and had been in the engine for 18 months at the time of the report. This is six months over the recommended 12 month service interval.

hilux diesel oil analysis results

From this report you can see:

  • Soot levels are normal.
  • Engine wear is normal, since high engine wear would be flagged by high metal contamination.

The vehicle tested has EGR. Therefore, based on the above two points, we can conclude:

The results of the oil analysis invalidates the argument that EGR causes excessive soot and engine wear.

I exceeded the 12 month service interval and the oil was in excellent condition. Viscosity was good and contaminants were low. Actually the oil was so good that the technician at the oil laboratory suggested I could go at least another 2,000km on this oil. He suggested I do another 2,000km then re-sample to see if it could be extended even further. This is on a completely standard, unmodified engine with a fully functional EGR system.

I wasn’t interested in pushing the limits on engine oil service intervals. It would cost me too much time and money in oil sampling. I was happy to know that after 10,000km and 18 months I still had plenty of margin in the oil’s lubricating performance. This gives me some room in case I do lots of short trips or drive the vehicle particularly hard or don’t get a chance to immediately service the vehicle when it’s due. I’ll stick to my 10,000km service interval. For more details on service intervals, check out this article.

If you want to find out for yourself whether your engine is wearing out too quickly and whether your oil has too much soot, you too can have oil analysis done on your oil. You should use those results, rather than information from fairytales posted on the internet, to determine whether you believe EGR is causing your engine to wear out quickly.

EGR and Engine Performance

Under medium to full load, the EGR valve is fully closed. This means EGR has no impact on engine performance. The valve is closed to not limit peak engine power, otherwise we’d need unnecessarily oversized engines to meet power requirements. Whenever you want performance the EGR valve is fully closed. Blocking it would make no difference. Any reports of improved performance by blocking the EGR can be attributed to confirmation bias, placebo and poor experimental method.

Actually, a partially blocked EGR can reduce performance, since the EGR valve will have to open more and therefore take longer to close when requested to close. When you plant the accelerator pedal the lag until the EGR valve is fully closed will be longer.

Some people use the fact that the EGR valve is closed at full throttle to justify blocking it. They say some sort of rubbish like:

“The valve is closed when emissions reach their peak so therefore it does nothing”.

People with arguments as stupid as that shouldn’t be allowed to post on forums. They are making people dumber.

Of course emissions are a function of the entire operating range of the engine. Since most of the operating time of an engine is at cruise or light acceleration, EGR has a massive impact on reducing NOx. Obviously disabling EGR must also have a massive impact on increasing NOx.

People will use the “it’s like eating your own shit” argument to suggest that EGR negatively impacts performance. The eating your own shit argument can be disregarded. It’s an attempt to emotionally validate a position by someone who doesn’t understand what is happening. It’s more like re-breathing your exhaled breath to avoid hyperventilating.

EGR and the Overall Design

Initially the EGR system would have been treated like an add on device to meet emission standards. With time it has become integrated into the engine’s design. Engine design has been developed with EGR as an integrated part of the engine and the system as a whole has been optimised with the EGR being part of the design. This means that modifying the EGR throws that optimisation out the window. Tinkering with the EGR will have unintended consequences. For example EGR may be used as part of the engine’s integrated air management, where the EGR helps to regulate the air-fuel ratio. It may be used to heat the engine quicker, reducing the time it takes for the engine to reach operating temperature and therefore reducing wear and improving fuel economy. In turbocharged engines it may be used in the control architecture for the turbo, helping to regulate boost pressure and determine the vane positioning for the variable geometry turbo. It may be used to cool the exhaust valves and turbo, helping them last longer. It may allow higher compression ratios to be used, improving fuel efficiency. In petrol engines EGR is used to reduce pumping losses and therefore improve fuel efficiency.

So if you modify or disable the EGR system you’ll be negatively impacting other systems as well.

EGR and Fuel Economy

For petrol engines, EGR improves fuel economy by reducing pumping losses. EGR also helps control engine knock, allowing leaner mixtures to be used, further improving fuel economy.

There’s not much valid information on how EGR impacts fuel economy in diesel engines. There is one source that is often quoted from the report “REVIEW OF THE 21ST CENTURY TRUCK PARTNERSHIP 2008″. The exact quote from the report is:

“A 3 percent decline in absolute engine efficiency is associated with the introduction of cooled EGR to meet the 2002 emissions standard. An additional 1.5 percent degradation in engine efficiency is forecasted to occur with increased EGR to meet the 2007 emissions standard. Improvements in the engine configuration were portrayed as having the capability to recover this absolute 4 1/2 percent engine efficiency decrease at the 2007 emissions standard.”

So when EGR was first introduced in 2002 there was a 3% step change degradation in engine efficiency. Three percent isn’t much – it’s less than what your average Joe could ever detect given all the uncontrolled variables when attempting to measure fuel economy.

When a new constraint is introduced to a system the initial step change is the worst it ever gets. Over time, as the technology matures and knowledge improves, the constraint gets optimised and fully exploited. The gap gets closed. The 3% drop in engine efficiency was measured way back in 2002 when the standard was first imposed. Do you think it’s likely that, in the many years since, engineers have been able to improve on that 3% drop? Typically, as the design for a system matures over time, the initial negative impact from an artificially imposed constraint gets eroded away.

Rather than reading the 3% decline in efficiency in isolation, you’ll see in the remainder of the paragraph that the actual people involved in engine design predicted that the gap would be fully closed by 2007. That was forecast to occur many years ago in 2007. What have they managed to achieve now? Where has technology taken us now? How expert have engineers become at simultaneously reducing NOx and improving fuel consumption? Unfortunately I cannot find any recent data. What we know is, at worst, EGR may negatively impact fuel economy by a few percent. More likely, the impact is much less than that, or maybe even non-existent, especially since CO2 emissions and fuel economy are so important now. This validates the conflicting reports that both blocking and unblocking the EGR improves fuel economy. The effect is small and can’t be measured by amateur testing. Reports of improved fuel economy can be attributed to confirmation bias, placebo and poor experimental method.

Any ridiculous claims of 20 or 30% improvements to fuel economy by disabling EGR you can immediately disregard. Forget about it. The automotive industry isn’t going to throw away that much fuel. Imagine the competitive advantage of the company that decides the break the mould. Those guys would make squillions!

Check out this article for methods of improving fuel economy that actually work.

Sooty EGR Valves and Air Intakes

Some people post photos up on the internet of EGR valves and air intakes / manifolds with lots of soot accumulation. They use this to support their position that restricting the EGR valve is a good idea. Are people really that stupid? Surely you’d have to have a carefully controlled experiment comparing the soot accumulation before and after EGR valve restriction to use it as evidence that EGR restriction is a good idea? How can a photo taken before the EGR restriction was installed tell us anything about the impact of an EGR restriction?

Photos of sooty EGR valves and sooty air intakes does not validate that an EGR restriction helps to reduce the soot!

Yes EGR does cause soot accumulation. Does an EGR restriction help reduce it? NO! As described above, EGR flow does not change when an EGR restriction is introduced, since the system compensates by opening the EGR valve more. Anyway, according to well established fluid dynamics science, the chance of a suspended particle settling on a surface increases when flow rate is reduced. So if you could reduce the EGR flow rate it would increase the soot accumulation.

If you want to reduce soot accumulation then you can install a catch can. Catch cans remove the oil from the gas flow which may prevent the soot from becoming sticky, although I have never seen a good experiment to verify that catch cans actually eliminate or reduce soot accumulation. Keep in mind that catch cans aren’t perfect. Like all things, they involve compromise and have both pros and cons. They can be used by vehicle manufacturers as a way out of warranty claims. The internal elements could break apart and get sucked into the engine, causing major damage. They can over-pressurise the crank case causing seals to blow out. Even if a catch can doesn’t cause a major seal failure, it can slowly increase seal wear and the likelihood of small oil leaks, since the crankcase must be operating at higher internal pressure due to the restriction that the catch can presents. It’s also possible that eliminating the oil flow over the intake valves could lead to reduced lubrication and accelerated wear.

Assuming You Can Restrict EGR

Despite the closed loop system, lets assume on your particular vehicle that partially blocking the EGR does reduce the flow rate and results in a myriad of wonderful advantages. This means the system does not compensate for the restriction introduced by a restriction plate. Similarly the system mustn’t compensate for soot accumulation. Good news for you: simply sit back, relax and let the soot accumulation do the job for you! Eventually it will restrict itself to the exact same amount as a restriction plate. You can now enjoy all the advantages of a restricted EGR without the hassle of purchasing and installing a plate. And you also keep your vehicle completely legal.

So now you’re EGR flow rate has been reduced. Combustion temperatures will go up along with the associated heat loading and engine wear. Some people argue that, since the EGR valve is closed at full load, peak combustion temperatures are not altered by restricting the EGR flow. Therefore there isn’t any impact to engine wear. Wrong! Although peak combustion temperatures may not change, the operating temperature distribution will change with reduced EGR flow. It will shift to higher temperatures. Engine wear is a function of the entire temperature distribution, not just the peak temperature. The distribution will look something like the graph below.

EGR Effect on Temperature

Your engine will be wearing out more due to higher temperatures. There is no way to avoid it. The fact that the EGR is there to reduce NOx is irrelevant. If you increase temperature you increase wear. This is true for any starting conditions independent of the reasons for the initial conditions.

Apart from increased wear from a higher temperature distribution, the EGR restriction will also negatively impact other systems as identified in the “EGR and the Overall Design” section.

Diesel Particulate Filter (DPF)

Diesel particulate filters reduce the soot emitted into the atmosphere. With DPF you can enjoy less lung disease, less cancer and less cardiovascular disease.

The filters are designed to minimise resistance to flow and do not significantly restrict exhaust flow provided the filter is adequately maintained through regeneration cycles. If the filter is allowed to become blocked it will restrict exhaust flow and increase fuel consumption by a few percent.

There’s been some bad press related to DPFs not regenerating properly, becoming blocked and requiring expensive cleaning or replacement. Although there have been some teething issues with this new design, usually the problem lies in the application of the vehicle and not with the vehicle itself.

If you own a diesel vehicle and it is unable to successfully regenerate, then you’ve bought the wrong tool for the job. The vehicle is not at fault. You are at fault. You’ve bought something designed to haul several people and their gear several hundred kilometers. Instead you’re using it to zip down to the shops or run some local errands. You’ve messed up. The right tool for you is either a pushbike, a scooter / motorbike, public transport or at worst a small petrol powered city car.

If you’re vehicle is unable to successfully regenerate, the solution is not to try to illegally modify it to correct your poor vehicle choice. The solution is to sell it and buy something more appropriate. Toughen up, take your medicine, admit you were wrong, take responsibility for the environment, buy something more appropriate and be more careful in the future before deciding to jump on the band wagon. Car dealers aren’t in the business of giving advice. They want to sell you a car even if that car is not right for you. It’s up to the buyer to figure out what is right.

If you really want to keep your inappropriate vehicle then you should understand that you are squandering money on a way over-specified form of transport. The extra cost associated with the DPF not regenerating properly is not special. It is just a small component of your overall squandering.

Some people argue that, since the regeneration cycle ultimately sends all the filtered soot into the atmosphere, the DPF does nothing. I feel bad when our education system fails. People with arguments as stupid as that shouldn’t be allowed to communicate on the internet. The DPF captures toxic soot and releases it as non-toxic carbon dioxide and water vapour.

Catalytic Converter

Catalytic converters simultaneously reduce hydrocarbons, carbon monoxide and NOx in both petrol and diesel vehicles. What a great device! You can enjoy all the health and environmental benefits afforded by significantly reducing these toxic emissions.

A properly working catalytic converter does not present a significant resistance to exhaust flow. It’s designed to minimise any resistance to flow. The negative impact to fuel economy and engine performance is so small it would not be noticeable or measurable outside of the laboratory. Ridiculous claims of catalytic converters increasing fuel consumption by 10 or 20% can be disregarded. The automotive industry would never throw that much fuel away. Imagine the competitive advantage of the company that decides the break to mould. Those guys would make gazillions!

If a catalytic converter is very old, blocked or has melted, then it may reduce engine power and fuel economy in the order of a few percent.

Emission Standards Do Not Reflect Actual Emissions

Sometimes I see this argument to support modifying or disabling emission systems:

“Engine control systems are optimised to pass the emission test cycles. Outside of the test conditions emissions are much higher. Therefore emission control is rubbish.”

Emission standards and test cycles are not designed to predict real world emission levels. The standards form a baseline for engine design and enable relative comparisons and trends to be made. You can think of the numbers defined in the standards as unitless indicators. They do not relate to any specific level of real world emissions. However if the indicator goes down then real world emissions also go down. The actual value of the numbers are irrelevant.

There’s no way around it. Stricter emission standards = less real world emissions. Disabling the emission control system = higher real world emissions. Obviously the emission standards and test cycles aren’t perfect. Nothing is perfect. They can be made better so that the testing sequence is closer to real world driving conditions.

Another stupid comment I’ve seen is:

“Emission standards are measured in per unit volume of exhaust gas. So it’s easy to fudge it by diluting the exhaust.”

What a dumb comment. People just make shit up in their head and post it on the net as if it’s fact. Emission standards are measured by total exhaust volume per unit distance traveled. It doesn’t matter how you dilute it. You can verify this by searching for the various specifications for the EURO series of emission standards.

Environmental Benefits

The science behind vehicle emissions and engine design is mature, well established and generally accepted. If someone is claiming environmental benefits from modifying or disabling emission controls, you need to immediately run away! They’re desperate to validate their position and are taking an extreme view to do it. It’s not even worth engaging in a discussion with such a ridiculous view.

If someone suggests that modifying or disabling emission controls is good for the environment what they are saying is there is no compromise involved with the change. Not only is it good for engine life, power and economy, it’s also good for the environment. Only advantages, no disadvantages. If someone ever suggests that a particular modification offers only advantages and no disadvantages then you should immediately be skeptical. This applies to everything, not just vehicle modifications. Everything involves compromise. If someone thinks they can simultaneously improve engine life, power, economy and reduce emissions then they need to immediately start an automotive design consultancy and make squillions of dollars.

Ever been driving behind an old truck and smelt that toxic exhaust? The emissions are real. Your nose proves it. The negative effects on health are real. Emission levels high enough to see it and smell it I’d suggest are pretty bloody bad for you even on short exposure. Much lower concentrations will still accumulate to significant health effects if the exposure is long term. Is it fair to pump that crap into the lungs of the guy behind you?

In the research paper “Health impacts of transport emissions in Australia: Economic costs“, which can be found with an internet search and downloaded for free, it is estimated that transport emissions cause around 1450 deaths per year in Australia. That’s more than the typical number of motor vehicle accident fatalities per year. It’s not a small amount of people. If you modify emission systems you are killing people. There’s no way around it. I’d suggest that putting up with a vehicle with emission control systems is not as bad as dying prematurely of cancer or heart disease

The same research paper estimates transport emissions cost the economy about $2.7 billion per year.


On the internet they call disabling emission systems deleting. There is a delete fad emerging. Delete everything you can as fast you can. Some people are so emotionally attached to modifying or disabling emission control systems that they’ll use scaremongering tactics to try to convince you they’ve done the right thing and that you should do the same. They’ll behave as if there’s some sort of emergency that you need to urgently address. They’ll tell you that the emission control systems are causing massive damage to the engine, costing you huge amounts of money, wasting tonnes of fuel and destroying the environment. They’ll make ridiculous claims like fuel economy can be improved by 30%, engine power increased substantially, the oil kept so clean you can use it in your salad whilst making the exhaust smell like the finest perfume and that there’s some conspiracy in the automotive industry that’s trying to suppress all these great advantages. There will be no good data to back the claims. I suggest you don’t listen to these extreme views. Find some better sources and do you own research before succumbing to the pressure or jumping on the delete band wagon.

For me, I’m pretty interested in not getting cancer or heart disease and not living with acid rain and smog. I also enjoy keeping my car legal and not paying fines. The supposed benefits of modifying the emission systems are in my opinion immeasurably small or non-existent. The disadvantages are real. So I won’t be touching the emission control systems on my vehicle.

How To Really Improve Performance, Economy and Longevity

To improve performance you need to dump more fuel (and air) into the engine. You’ll suffer poorer fuel economy, reduced engine life and increased emissions. If you have a diesel one way of getting more power is by using a diesel performance chip.

Check out this article for ideas on how to improve fuel economy.

If you’re interested in engine longevity the best things you can do are:

  • Avoid short trips with a cold engine.
  • Allow a short idling warm up period on a cold start (say 30 seconds).
  • Allow a longer warm up period of a few minutes if your journey will immediately be at high speed or up a long hill.
  • Be very gentle with the engine when it’s not up to operating temperature.
  • Service according to the manufacturer’s recommendation.
  • Drive smoothly, avoid shock loads.
  • Drive economically. Less fuel burnt means less work by the engine and less engine wear.
  • Avoid vehicle modifications. Most modifications make a vehicle heavier, less aerodynamic, more powerful or compromise elements of the original design. Usually engine load increases.

I think the biggest contributor to early engine failure, provided the vehicle is serviced properly and not abused, is too many short trips / too much cold temperature operation. The evidence is the massive mileage that taxis and couriers get on their vehicles. Cold operation is bad in so many ways. On a cold start there is initially no oil flow until sufficient oil pressure has developed, resulting in poor lubrication and high wear. Cold operation lets water (a major combustion product) accumulate in the oil, degrading lubrication. The oil is not at correct viscosity for maximum protection, further degrading lubrication. Contaminants from imperfect combustion are much higher during cold operation which accumulate in the oil. Clearances and tolerances are out of spec, increasing wear on various surfaces inside the engine. Piston rings have not expanded fully, allowing excessive contaminants into the crank case. Oil is washed off the cylinders due to the rich air-fuel mixture required to compensate for poor combustion efficiency at cold temperatures. This reduces the amount of oil protecting the pistons and increases the amount of fuel in the oil, which further impairs the oil’s lubrication performance.

General Comment on Fuel Efficiency

Manufacturers are going to extreme lengths to improve fuel efficiency. It makes sense since fuel economy is one of the most marketable parameters of a vehicle. Do you honestly believe that manufacturers wouldn’t exploit a solution as simple as a slightly larger catalytic converter or diesel particulate filter to benefit from the extreme improvements in fuel economy that some people report is possible?

Do you honestly believe that manufacturers would allow a 30% loss in economy from EGR? Manufacturers don’t need to use EGR. They need to comply with emission standards any way they can. If there was really 30% fuel economy at stake do you honestly think manufacturers would put up with it? I don’t think so. They’d find another way.

What would you do if you were the boss of an automotive company and you could get a competitive advantage worth many millions of dollars from something as simple as a larger catalytic converter? Would it be worth pursuing?

With a bit of common sense you can immediately invalidate practically any ridiculous fuel economy claim.

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See also:

Diesel vs Petrol

Exhaust Pipes: Is Bigger Better?

Design Compromise

How Failure Works

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10 replies »

  1. Hi Joe, I really enjoyed your write-up on emission systems. Are you able to give me your opinion on the following?
    I purchased a used mercedes 8 months ago, its a 2008 C220 cdi, and its a grwat car, BUT, it blows black smoke when under load. Initially I thought the injectors might be the culprit, it has at least 220k on the clock (it has been wound back), it is also a bit too noisy in my opinion. Especially when its cold. A mechanic from an unnamed diesel tuning company, is suggesting that a chemical de-soot will fix the problem, for a mere $1100. The car does not show any fault codes and behaves well otherwise. It does have a bit of a rough idle most of the time, come to think of it. Im hesitant to take it to mercedes, cant afford another mortgage. What do you think? Michael S.

    • Hi Michael could be many things. You need to get an expert on your vehicle to get a correct diagnosis. Be specific, ask for a diagnosis, not for changing random parts or cleaning. If they don’t have the expertise to provide a diagnosis that’s ok, try somewhere else. Otherwise it’s likely you will spend money on stuff that isn’t required.

      I have no experience with Mercedes but what you describe could be worn injectors. On a hilux it is easy to check using a laptop with Toyota software that provides data on various fuel system parameters. There should be something similar with Mercedes.

      Could be dirty air metering instrument, could be air leak somewhere in intake, could be dodgy EGR valve, could be dodgy fuel pressure control valve. All these things can cause too much fuel, not enough air, and resulting black smoke.

      A cheap and easy thing for you to try is cleaning the mass air flow sensor. There should be a sensor in the intake somewhere that can be easily removed. Spray it with a heap of contact cleaner. This is an easy thing to try so can be done without a proper diagnosis (and should be done every service anyway).

      You might want to try a vehicle specific forum, you might get some answers there.

  2. Hi OBJ, after reading this page I’d say your underlying wishes are pretty clear….not wishes that I necessarily agree with but wishes that are certainly clear……..I’m not saying that you want everyone to vote Greens but your musings for a clean, green internal combustion world contain several contradictions – as these types of musings usually do.

    Okay here’s the issue as I see it.

    You tell us repeatedly that all modifications, all changes are a compromise, for every action there is an equal and opposite reaction somewhere down the line, which are statements I totally agree with. However you then spend page after page breaking down each component of exhaust systems carefully explaining how each added component does not in involve any detrimental compromise and telling readers that there is no downside in the case of ever increasing vehicle emissions controls.

    You in fact argue at quite some length that these introduced and ever-stringent controls involve no compromise to the power, operation or fuel efficiency whatsoever to modern internal combustion engines. You are the only person I know of that believes that.

    Many people are happy with the compromises with emissions to help assuage their environmental concerns but please don’t try to convince sensible people that this does not involve compromise of some sort. That would be called a double standard.

    You are probably feeling a little annoyed at reading my words as people riding this crusade usually do when faced with some truths that run contrary to their chosen beliefs and wishes but please read on.

    You are quite entitled to advise us that without emissions controls that many more of us will die prematurely of cancer, heart and lung disease and any number of other hideous illnesses. Yet this is coming from someone who has proudly made a living from driving a large 4WD hundreds of thousands of kms around various parts of the planet to his hearts desire, and I say good luck to you however…….you are telling us…..it is good for me, but not for thee.

    Surely if the people’s health, the welfare of the planet and indeed the future of humanity (if we do listen to the scaremongers) is so important how can anyone who believes this and preaches this belief to others comfortably have spent so many hundreds of hours driving around and belching out planet destroying emissions for fun?

    Can you see a touch of hypocritical here? People who like to ride on the high horse always seem to get themselves compromised (there’s that word again).

    Joe I’m sure you are a good bloke and I’m just as sure you don’t like what I’ve written but if you are honest with yourself you will see and understand the contradictions I’ve described. If you can consider advice from a stranger I would say keep writing your blog, it is very good overall, but resist the temptation to become preachy. Stick to the mechanicals and the fun adventures and you will stay on a winner.



    • Hey Chris which article did you read? Can you please reference where I state there is no compromise in emission systems? Or are you just making shit up? I’ve had people use this argument before. “You say the factory suspension is perfect in every possible way” or some bullshit similar to yours. No, there’s nothing like that in any article on this site. You’ve misunderstood, or deliberately lied to validate your own position.

      The only way to stop environmental destruction is to stop living. Otherwise you need to pick somewhere on a spectrum where you think is a good compromise between living life and allowing everyone else, current and future, to live their life. In that case, according to you, everyone is a hypocrite, unless they immediately commit suicide.

      It’s not about being on a high horse. It’s just that in my opinion the benefits of bypassing emission systems are extremely small, relatively minor compared to a premature death from cancer, and massively overstated by the consumer sucker culture of the motoring community, and exploited and perpetuated by those that make profit from it.

      The point is if you’re gonna drive a car you might as well not kill people unnecessarily. And you might as well not unnecessarily waste money on gizmos that don’t really make you happy.

      The hypocrite card is an easy one to pull, rather than using logic or science to explain something. It’s hard to accept that maybe you’ve been a bit of a dumb consumer sucker spending money on stuff that simultaneously kills people whilst providing no significant benefit. It’s cultural, you’ve been trained in the consumer thing you’re whole life, culture is hard to change, and so dumb arguments are resorted to.

  3. Joe, your blog is one of the most useful, unbiased, well-researched sources of information on setting up a vehicle for outback touring that I know of (and I follow quite a few). It is great that you try and account for human and corporate bias. I am very thankful of your efforts!

  4. Top article and 100% agree with your philosophy on unnecessary mods sold to the masses with brainless forum-hype and nonsensical marketing jargon. I own the same model of hilux and after 180k the limp mode gremlin appeared a few times when on the freeway, quite dangerous when overtaking! I had to fork out $2.2k to Toyota for a new egr cooler and an intake clean. Needless to say a catch can with pressure valves is now fitted (provent). Impacts on the crankcase seals were a concern, however I can hear the valve operating at low revs before the intake vacuum builds up (quite noisy). It is probably worth noting that carbon cleaning vac systems are becoming more prevalent with good mechanics and may be a good preventative measure for egr related carbon build up. Happy travels.

  5. Thank you I found this helpful. I will install a provent catch can on my turbo diesel but scratch the plan for a diy resistor mod to disable the EGR. More me it’s the moral argument: I prefer cleaner air for me, my kids and other people, or species, and the future. I had been lured by good folks on a forum assuring everyone they had improved fuel economy but you have convinced me not to go meddling with a carefully tuned engine.

    I am surprised that you seem to place a lot of trust in car manufacturers. I would be interested to know your thoughts on the Volkswagen emissions scandal which – I know from European contacts – was widely known about for years well before it was proved and went to court. Senior leaders knew it was illegal but authorised it anyway. That makes me wonder if your trust in engineers is entirely justified. My sense is that the emissions regs in Europe have been so strict that companies were (and are?) willing to do all kinds of dubious, illegal or long-term counterproductive things to keep selling hydrocarbon vehicles. I can imagine that DPF and EGR are not things manufacturers “wanted” to do, but were compelled to do by legislation. So while I agree that these technologies aren’t inherently bad, I suspect the legislation might have distorted the purity of the engineering compromises.

    Current car makers know they are fighting a losing battle with emissions standards. 100+ years of automotive design has fine tuned cars, but we are ripe for new advances based on contemporary strong and light materials, powerful batteries and electric engines. Sure they haven’t got decades of engineering precision yet, but they are the future. It will take time for these advances to suit the challenging Australian terrain and convince the jokes-of-government we keep electing, and perhaps win over the stubbornly closed-minded car buying market here.

    • Hey TV I don’t trust large corporations to behave ethically at all. The leaders are generally greedy narcissists who will attempt to get away with as much as possible. VW are not unique, they just got caught pushing the limits a bit too far.

      That’s got nothing to do with the finely tuned design of an engine. Everything is there for a purpose, and in complicated systems whenever you tinker there will be unintended consequences. The ethics behind the design are irrelevant.

      The companies want to make as much money as possible. If there are cheap and effective solutions to problems they will automatically be adopted regardless of the ethics of the leadership. Companies will provide a reliable product with as much power and economy that they can safely squeeze out of the design as possible, not for ethics but because that’s how you make money.

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