Symptom Definition

WARNING: This page does not describe the selected car, but rather 10 other vehicles, including the 1994 GMC Vandura Special, 1994 GMC Vandura, 1994 GMC Rally Camper Special, 1994 GMC Rally, and 1994 GMC Forward Control. However, it is still accessible from the selected car via links, so may be relevant.

Fuel ignites in intake manifold or in exhaust system, making a loud popping noise.

Possible Causes & Corrections:

Ensure EGR valve is not always open.
Check engine for sticking or leaking valves.
Check for proper valve timing.
Check for engine vacuum leaks. Ensure engine is tuned to specifications.
Using Spark Tester (ST-125), check available output voltage of ignition coil.
Check for crossfire between spark plugs, distributor cap and spark plug wires.
Check for an intermittent ignition system problem.
Check for erratic spark timing or distributor reference (RPM) signal.
Ensure initial ignition timing is properly set.
On some 5.7L engines, check for faulty air injection diverter valve or check valve.
Check for fuel or water in vacuum hose to MAP sensor. Also check for restricted hose.