before and after

Carbon build-up on an intake is like lung cancer for your engine and can make the engine work harder and struggle for air.

IN A WORLD where free information reigns supreme, it’s often difficult to find the diamonds in the crap. All it takes is a quick search online to find thread after thread of ill-educated opinions sprouting off some nonsense about whatever happens to be the latest trend in internet-land. $30 canvas seat covers apparently as good as Aussie-made gear, humongous suspension lifts that’d rival Goliath in terms of size and likelihood of failure, and the latest hair-brained idea that seems to be gaining momentum faster than a rich, old billionaire – removing emissions equipment for such incredibly valuable reasons such as “it sounds better” and “me mate did it and loves it”. It’d almost be comical if it wasn’t having a serious effect on engine longevity.

What we’re referring to is the growing trend of tampering with and removing important emissions systems such as Exhaust Gas Recirculators (EGR) and Diesel Particulate Filters. To get to the bottom of it we’ve gone straight to the source, with three of the best diesel experts all throwing their weight into an on-going battle between good and evil, the underdog and the all-powerful government, and internet modifications and common sense. Enrolled this month are Andrew Leimroth from Berrima Diesel, Paul Farrell from Geelong Performance Centre, and Stephen Booth from PowerTorque Victoria.



WE ARE big proponents of the internal combustion engine around here. They’re fantastic inventions that have given millions of people the ability to travel long distances with a load in relative comfort. That said, they do have a downside, and if we’re perfectly honest, it’s a real a doozy.

Forget all the back and forth about climate change and emissions effects on the earth, it’s a scientific fact that diesel emissions cause lung damage, respiratory problems, acid rains, smog, and cancer in humans. It’s a direct result of the various emissions they produce such as Carbon Monoxide (CO), Hydrocarbons (HC), Nitric Oxide and Nitrogen Dioxide (NOx), and soot or (NOx), and soot or Particulate Matter (PM).

Scary stuff, right?

It should be if you like breathing. The good news is manufacturers have their feet held to the fire by various agencies in a bid to reduce emissions and improve air quality.

They’ve been forced to do this by implementing a few now reasonably common emission systems. “The two most types (of emission control) are Exhaust Gas Recirculation and catalytic convertors,” Andrew told us.

“In more recent times Diesel Particulate Filters (DPF) have also become more common.” These three systems all work in varying ways. Catalytic convertors, most commonly found in petrol 4x4s and more recently in diesels, are used to convert carbon monoxide, hydrocarbons and nitrogen oxides into less harmful carbon dioxide, water and nitrogen. DPFs add another layer of complexity, aiming to break down large diesel particulates (soot) into smaller, less harmful ash.

Paul added: “Similar to a catalytic convertor, a DPF removes diesel particulates from the exhaust gas. There are pressure sensors either side of the DPF which are monitored by the vehicle’s ECU. When the pressure gets high enough, indicating a certain amount of blockage, the ECU commands what’s known as a burn.

The injection timing is retarded, which heats the DPF to a very high temperature and burns the particulates out of the DPF.”

Another system known as SCR (selective catalytic reduction) injects a mixture of deionised water and urea, commonly known as AdBlue, in a further attempt to reduce diesel soot. “It’s mostly in the American stuff,” Stephen added. “They’re usually a stage of emissions ahead of us.”


WHILE most common emissions systems are designed to deal with harmful pollutants after they’ve been made – filtering them out in various ways – EGR is designed to prevent them being made in the first place. NOx is formed when nitrogen and oxygen molecules are present with temperatures north of 1500°C and is responsible for the smog often seen in cities, as well as acid rain.

As diesel engines rely on heat rather than spark to ignite, NOx has been a constant problem when talking diesel emissions. One way manufacturers have tried to curtail the production of NOx is to lower combustion temperatures.

“What an EGR does is effectively plumb hot exhaust gas from the manifold back into the intake, re-burning exhaust gas.” Paul said. “The end result is less emissions out of the tail pipe.”

The net result of this is replacing flammable oxygen with inert exhaust gases, causing a colder combustion cycle and lower levels of NOx formation.

However, things aren’t always how they seem. Andrew brought up the point that while the basic design of an EGR system hasn’t changed drastically, their purpose has. “EGR was about NOx emissions before, but that’s sort of evolved with the new diesels having much lower compression than old,” he said. “Instead of running at around 450- 500psi they’re getting down as low as the 300s using high pressure common rail injection, precise timing and multiple injections to get a good burn at lower compressions.” All of this results in naturally lowered NOx emissions, leaving the EGR there for efficiency reasons rather than emissions.


ON PAPER an EGR sounds like a pretty damn good piece of kit to have on any 4x4, allowing the manufacturer to control combustion temperatures, reduce emissions, and do so with minimal complexity. Why then are so many people rushing to block off or even remove these systems? “Eventually the EGR gunks up the intake system,” Stephen said. “The combination of oil and vapor combined in the inlet manifold clogs it up.” The oil vapor he’s referring to is caused by engine blow-by, a completely separate operation in an engine, but one that causes catastrophic issues. Around each piston in an engine are a series of piston rings, designed to help seal the combustion chamber and allow the forces of igniting diesel or petrol to push down on the piston, rather than past it. The problem is these rings don’t make a perfect seal.

As the engine runs through its strokes small amounts of pressure are able to escape past the piston rings and into the lower half of the engine, pressuring the crank case. To relieve this pressure, manufacturers fit a breather to the top of the rocker cover that allows the oilmisted air to escape. Rather than this misted air venting into the atmosphere it’s plumbed into the intake, the result is a thin film of oil coating the inside of the intake manifold right through to the combustion chamber.

When the spent exhaust gases are reintroduced to the intake they stick to the oily residue and build up. “With the two of them combined it’s a recipe for disaster,” Andrew said.

“The inlet manifold gets blocked up, but it’s only because it’s all oily and wet. If the EGR was by itself it wouldn’t happen anymore than you would see in an exhaust pipe. It’s not really there to recirculate the soot, but by the nature of a diesel engine it does bring them through.”

Paul added that on his routine services he often comes across clogged intakes that require a full strip-down to clean. “We’ve seen the intake ports blocked down to less than 50 per cent of their original size.”



RATHER than an EGR being the issue as so many people believe, the problem is the inlet manifold becoming clogged from a build-up of oil residue and exhaust soot.

Remove either one and there’s no longer an issue. Luckily, one is a whole lot easier to do than the other. “Most people can get away with fitting a decent catch can like a ProVent to remove the oil vapor,” Stephen said. “If that’s done, most of the exhaust gas soot goes straight through without sticking to the inlet manifold.”

It’s worth mentioning there are varying quality levels when it comes to catch cans, with a price spectrum that ranges from spare change to a few hundred dollars. On the budget end is your typical alloy box with an inlet and outlet. The problem is these rely on magic to remove the oil from the air, which isn’t too successful and can often have issues like reduced openings that can cause a build-up of pressure inside the engine. This can cause gaskets and seals to blow out from the inside, resulting in an engine literally pumping its oil out the dipstick tube.

Quality items will generally run a filter element, which will remove the oil from the air as it passes through and drastically cut down any oily residue in the inlet track and prevent the exhaust soot from building up. These filters are often either plumbed back into the sump, or are manually drained to remove the oil build-up. To prevent over-pressurisation if something is clogged, they’ll often have a pressure release system as well.

The other, more drastic approach is to remove the EGR system itself. With no exhaust soot going through the intake system there’s nothing to stick to the oily residue. In simple engines this can be achieved by physically installing a blockoff plate that will stop the gases flowing through the system, although most modern engines will register the block and throw a fault code, possibly causing your 4x4 to go into limp mode.

In many late-model vehicles a custom tune can instead stop the valves from ever opening, but that does come with more issues than it’s worth.


BERRIMA DIESEL SERVICE Ph: (02) 4877 1256 W: www.berrimadiesel.com GEELONG PERFORMANCE CENTRE Ph: (03) 5277 2503 W: www.geelongperformance.com.au POWERTORQUE VIC Ph: 0417 558 799 W: www.facebook.com/powertorquevic


THERE are a few considerations you’ll have to make when you find yourself with that cheap block-off plate and a set of screwdrivers in hand. The first and most likely to make people pause for consideration is warranty.

Most manufacturers are well within their legal rights to knock back any warranty claims that are even loosely related to a modification you’ve made, legal or otherwise. As the EGR system is directly related to a turbocharger, failure down the track could see you out of pocket for any repairs, even unrelated problems where the EGR removal shouldn’t have caused an issue can still see you in a battle with Fair Trading to get things fixed.

From there the serious risks start. Sure, you’ll cop an on-the-spot fine from Mr Plod for driving a defective vehicle if you’re found, but there are much bigger things to be concerned with than that.

The NSW Protection of the Environment Operations (Clean Air) Regulation of 2010 states: “The owner of a motor vehicle who uses the motor vehicle, or causes or allows it to be used, must ensure that at the time of that use, any antipollution device that has been fitted to the motor vehicle has not been removed, disconnected or impaired, or adjusted or modified in such a way as to result in the emission of excessive air impurities by the motor vehicle”.

The penalty that little piece of legislation can net you is 200 penalty units as an individual or up to 400 as a business.

Big deal, right? Well, it would be if penalty units weren’t around $150 a piece in some states. That’s a maximum fine of near on $30,000 for blocking or removing your EGR system or DPF from your exhaust.

Are you likely to get caught? Probably not, but don’t go bragging about it on social media, either. At the end of the day there are smarter ways to get the job done that won’t ruin you financially.