Hello. My son has a 2001 GMC Safari with a 4.3 engine. He complained of a “rough idle” along with a coolant leak. Not knowing what the rough idle might be, I suggested he bring a new set of spark plugs. I listened to the engine then looked and found a bad left side motor mount, which I replaced along with the spark plugs. I pressure tested the coolant system and found coolant leaking from the left front of the intake manifold.
I replaced the intake manifold gasket. When I first started the engine it ran poorly then cleared up and ran good. During a test drive, the engine started running rough again, it sounds like the spark timing is off, running on three cylinders, pinging and popping, then it will clear up and run good.
The only DTC set was PO300 or Random Misfire. I checked, wiggled all the sensor wires to no avail. I have brought the #1 cyl to TDC and checked the distributor for rotor pointing to the #1 post and/or the “6 arrow”. I have replaced the crank and cam sensors, distributor cap and rotor and ignition module and the problem still exist. I changed the distributor gear and shaft, problem still there. To be thorough, I put the old plugs back in and checked compression, 180 lbs on all cylinders. Still runs bad. What am I overlooking?
You may have sticking injector nozzles. These are pretty common.
Thank you, When I check fuel pressure I get 60 psi while the pump runs, key on/engine off. As soon as the pump shuts off, the pressure drops to zero. I thought pressure should hold even with the pump off but some wrench friends told me it was normal for the pressure to drop like that. Which is normal?
Fuel pressure dropping is NOT NORMAL. A slight drop is normal, say a few LBS. Need to find out why the loss of pressure-Fuel pump check valve, which is part of the pump.Stuck open injector or broken line under the intake. Fuel pressure regulator- also under the intake. See if the oil smells like gas because of an internal leak of a line, regulator or injector.
Fixed it. Guess I screwed the pooch somewhere, found a bolt laying in the intake, looked like it might have been catching the valves. Stupid, real stupid. Thanks for the replies.