Rough running old diesels are very common. You will notice a “hiccup” noise when the engine is idling. To keep your diesel engine functioning optimally and lasting a long time, perform the following checks to identify the cause of this problem. You can generally understand what is wrong with a diesel engine by the color of the smoke being emitted from the exhaust.

  • Is the smoke coming out of the exhaust pipe black? This is the most common diesel engine problem and indicates an imbalance in the air to fuel ratio, where part of the fuel wasn’t burned up and turned into black soot. If this is the case, the engine is probably only experiencing a short period of roughness during start-up. Common causes of black smoke are faulty injectors or injector pump, bad glow plugs, a faulty air filter, or a bad EGR valve. These problems will make the engine difficult to start, especially in colder environments, and it will misfire. Most of these issues are easy fixes.
  • Is the smoke coming out of the exhaust pipe white? This means that the fuel being injected into the combustion chamber is not being burned properly. In this case, the engine is probably experiencing rough idling both when it is cold and hot, and the problem will come and go. Common causes of white smoke are low cylinder compression, improper injector pump timing, and problem with the fuel injection system. As diesel engines age, the fuel injection system can start to “gum up”, and the injector tips begin squirting instead of misting. The injection timing can get out of whack. Wear and tear on the piston rings and cylinder walls result in lost combustion.
  • Is the smoke coming out of the exhaust pipe blue? This is caused by excess lubricating oil within the engine cylinders during combustion. The excess oil gets burnt and is emitted as blue smoke. This is a mechanical problem because engine oil should not be getting into places where it can be burned. In this case, the engine will usually experience a rough start-up, with the idle smoothing out after about 30 seconds. Typical causes of blue smoke are a worn out valve stem oil seal, faulty injector pump or lift pump, worn out cylinders or piston rings, turbocharger problems, or head gasket failure.

Once you have identified when the engine is idling rough and the color of the smoke coming out of the exhaust pipe, you will have a better idea as to what is causing this problem. A diesel engine in good condition should produce no visible smoke from the exhaust pipe. Bring your vehicle to a trusted mechanic near you for a complete diagnosis. If you are in the Meridian, ID area, call Gem State Diesel’s diesel engine experts for help at 208-288-5555.