Curing an Intermittent Rough Running Diesel Engine

This can be a real challenge if the problem comes and goes either warm or hot

Rough running old diesels are very common. Yes, we all heard that the engines can go forever - BUT are they healthy and happy during the journey? Kent can tell you from personal experience if they are not "happy" they will not go forever! If the problem is only a short period of roughness during startup it can be related to bad glow plugs or excess carbon in the pre-chambers. But what if the problem if the engine runs rough either hot or cold and the problem comes and goes?

Problem & Solution

Common among these chassis:


The cause is very seldom due to just one thing. With age comes wear. The fuel injection system starts to "gum up" and the injector tips start squirting instead of misting. The timing chain stretches and injection timing gets out of wack. The camshaft wears and the valves do not open or seat properly. The piston rings and cylinder walls wear resulting in lost combustion. The turbo starts to drag. The exhaust becomes plugged up. The lift pump does not deliver enough fuel pressure. The injection pump and delivery valves lose their mojo. The fuel tank gums up and the filter screen becomes plugged. You can have ALL these problems and the diesel engine will run, but it will become extremely ornery. 

A valve adjustment (on engines up to 1885) followed by a compression test must be done first. If the compression is weak or highly imbalanced you will not be able to solve the rough running problem short of an engine overhaul. If compression is good the very next thing that Kent recommends is to do a DIESEL PURGE. This is the very best medicine for sick diesels. Be sure to watch his on-demand video on doing a diesel purge on an OM617 engine.

If that does not help then it should move on to testing/adjusting or rebuilding your fuel injectors.After that it gets a little more complicated. Follow along with Kent's on-demand video as he walks you through the steps he takes to try to isolate the cause or cause of a rough running diesel engine.