My '02 van with a 5.2 is giving me a rough time. At part throttle, particulary at a heavy load, low engine speed (like accelerating in OD without kicking down to 3rd gear), the engine starts bucking and kicking and popping thru the intake. I can see the spark advance on my scan tool changing erratically- 10 degrees, 20, 32, 0, 15, etc.-it's all over the place, constantly changing, no real pattern. It even jumps around when it's idling. There are no DTC's. I did the normal tune up stuff before I noticed the spark advance issue-cap, rotor, wires, plugs just because it was due.Have changed the following parts chasing this problem- MAP sensor, TPS, cam sensor, crank sensor, govenor press/temp sensor, gov. solenoid, trans 3-4 solenoids, ignition coil, & PCM.

Engine idles fine, WOT is usually ok, but does occasionally have issues here. Fuel pressure is 48psig- never waivers. I unplugged the injectors one at a time thinking maybe there was an intermittent short- no change. All other temp sensors seem to be reading accurately. I checked the flex plate visually thru the opening for the CPS thinking maybe there was debris in one of the slots- nothing.

I am runnig out of ideas- thinking maybe oxygen sensors? The spark advance is definatley the issue, but what the heck is causing it??

Anybody out ther have any ideas??

 

For this to happen the spark plug is firing when the intake valve is still open or you are getting crossfire between spark plug wires or within the distributor cap.

 

Yeah, I agree about the plug firing when the intake is open, but all of these items are brand new. Turns out the the crank sensor I bought from one of the big parts chain store was bad out of the box. Got a US made part and helped with some of the problem, but the spark advance is still jumping around during part throttle-drops to 0 degrees then jumps up and down-, high load acceleration. The O2 voltage also is dropping to 0 at the same time.

 

Hmm, it sounds erratic. Have you checked the engine to body ground to see if it is good?

 

Might want to check the battery to engine ground as well.