QuestionI have problem with the engine surging while idling in park and in gear. Any suggestion on where to start to troublshoot?
AnswerSince all 6.2s are now at least 13 years old, surging problems typically fall into two categories:
The first is deteriorated fuel lines/fuel filter seals that allow air into the fuel before it reaches the injection pump. Diesels are very intolerant of air in their fuel because the injection pump cannot compress air.
The second is the injection pump itself. Internal parts wear out and can cause erratic running.
I would start with the fuel supply system at the fuel tank and work forward, looking for bad hoses and lines. At the fuel filter(s), check for proper sealing of the element(s) and ensure that there are no leaks. Finally, check the hose from the fuel filter to the injection pump inlet. In rare cases, the return system can plug and cause problems. Check all those lines, too.
If you have an electric fuel transfer pump, make sure that it is operating correctly. GM 6.2/6.5 diesels with electric fuel transfer pumps usually have problems with the oil pressure switch contacts that send power to the pump.
