EGR and Intake Manifold Build-up in the Common Rail Diesel

Brooke Hamilton

Common rail diesel engine issuesThis tech paper is specific to the EGR issues in Toyota Hilux and Prado with the 1KD engine, and the Nissan Navara YD25, however, the basic principles and solutions are relevant to most late model common rail diesel engines.


As part of an effort to reduce exhaust emissions, The most effective method of reducing NOX emissions is to lower the combustion temperature inside the cylinder. The main method employed by every manufacturer is to add some exhaust gases as inert gases inside the cylinder, reducing the amount of oxygen available for combustion during the power stroke, thereby lowering the combustion temperature.

While this method is effective, it also means that – especially for diesel engines – there is a gradual build-up of sooty carbon in the intake manifold and EGR valve. This issue is especially pronounced in vehicles fitted with an EGR cooler.

The Issues:

The main issue is that the crankcase breather hose provides a sticky film of oil inside the manifold, creating the tacky surface for carbon to stick to and build. In nearly every intake manifold, there is an elbow below the EGR valve, before the plenum, that runs into the head. Given that carbon has more weight than air, it also carries more momentum, and is therefore less able to make the turn around the elbow bend. As a result, it is always the cylinders closest to this elbow that receive the most build-up. As an example, the bend in the Hilux 1KD is next to the firewall, and therefore it is cylinders 4 and 3 that will show the most pronounced build-up, and the most pronounced oxygen restriction,

With this carbon material blocking up to 75% of the oxygen supply, and with this blockage significantly worse for some cylinders than for others, this definitely causes issues with engine performance.

Recommended Methods and Intervals for Repair:

If no steps have been taken to stop carbon from entering the manifold, then by the time 130,000 kms comes around, the intakes will definitely be in need of a cleaning. We recommend doing this with the injector changes as a necessity, if it has not been done before then.

Once the intake has been completely cleaned out, we believe that it is worth taking some steps to prevent build-up in the future.

The obvious, quick-and-dirty fix is to fit an EGR block-off plate, and stop carbon from entering the intake. The problem with this method is that in many modern vehicles, the vehicle will start throwing fault code after fault code.

One good way around the whole fault code issue with blocking off the EGR is to filter the crankcase breather line. We recommend fitting a HPD Catch Can to client vehicles. This oil mist filter will stop the oil film from accumulating inside the intake manifold, giving the carbon nothing to stick to. The complete setup including the mounting kit is around $375 for most vehicles and there are no ongoing costs with replacement filters. What these do is ensure that the vehicle is breathing the air it is designed to breathe, that there will be no drop-off in performance, and you will not have to get this dirty (on this car at least) again!