Engine Mechanical problem
1996 GMC Truck V8 Four Wheel Drive Automatic 190000 miles
I have a 1996 GMC Yukon with the 5.7 liter engine. The motor misses at an idle. The code says it is missing on the number 5 cylinder. I have done a compression check and found 140 psi on the #5 cylinder and a 150 psi on the #7. I have changed all the plugs and wires, in which the issue has continued although better for a short time. The plug fouls with a crusty white color. The engine also is idling fast at 1500 rpm with an error that the engine is idling faster than expected. If I pull the spark plug wire off of the number 5 plug, the engine does not change the rough idle at all. There does appear to be spark if I connect an old plug. Please point me in the correct direction. Thanks!
Check and test the injector for no. 5 for the fast idle clean out the idle air control valve and test the TPS
Engine misfiring can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel.