Diesel engine intake carbon build up issues


Diesel engine intake carbon build up issues,  we are seeing an increase I cases of inlet carbon build up in diesel engines coming through the workshop. With modern diesel engines running much more E.G.R to meet emissions requirements and extended service intervals along with poor quality fuel this seems to be on the increase. The build up of carbon restricts the inlet ports, throttle body and inlet manifold swirl flaps. The result of restricting the inlet is a lack of power, excessive exhaust smoke, sticking E.G.R valves and inlet swirl flaps .Usually by the time the vehicle is affected its too late and stripping and cleaning of the inlet system is the only solution a time consuming , dirty and costly repair.

We recommend to our customers regular servicing using good quality engine oils, using quality branded diesel fuel and a regular drive for twenty minutes with vehicles that only cover short journeys.

The Mercedes GLA 2.2 here is a prime example of the extent that carbon can build up in the inlet system.


Mercedes GLA


This vehicle came in with the engine management light on with faults for the inlet flap motor, an output test confirmed that the inlet flaps were sticking.


carbon build up
                                  Inlet manifold and swirl flaps






Throttle body blocked with carbon
Carbon removed from throttle body


inlet blocked with carbon
inlet swirl flaps


We haven’t found that various on car cleaning systems and additives can clean this extent of carbon from the inlet in fact it can create problems by forcing the carbon into the exhaust and then block the D.P.F there is  a case for preventative cleaning on a regular basis .


We were surprised at the extent of the carbon build up in all the inlet system at a relatively low mileage. The inlet manifold was removed and replaced with a new unit along with a new control motor. The throttle body was striped and cleaned and when rebuilt restored normal performance and correct swirl flap operation. An expensive job that may well have been prevented with more regular servicing using good quality oils and good quality branded diesel fuel.