Dieseling, Run-On

Engine continues to run after key is turned to the Off position, but runs very rough. (If engine runs smooth, check ignition switch.)
^ Check:
- Fuel injectors for fuel leakage.
Perform a fuel system operational test at the pressure test connector. Refer to "Fuel System Diagnostics."

Fuel ignites in intake manifold or in exhaust system, making a loud popping sound.
^ Check:
- Intake manifold gaskets for leaks.
- Misfiring, cross firing or cutting out under load.
- Spark plugs. Check for wetness, improper gap, cracks, burned electrodes and heavy deposits.
- Ignition system for moisture, dust, cracks, burns, etc.
- Check engine valve timing and compression.
- Check for worn or incorrect basic engine parts such as camshaft(s) heads, pistons, rocker arms, lifters, broken or worn valve springs, etc.