2002 Pontiac Bonneville SLE Intermittent Issue

[ChippaT]

I have a 2002 Pontiac Bonneville SLE. I've had an intermittent chugging issue that has progressively gotten worse. It feels like I'm pressing the gas pedal and letting off rapidly even though I'm at a constant acceleration. It happens on two occasions. 1) hard acceleration(3k+ rpms) in all gears. 2) when the torque converter locks up(55-65mph) and I'm going up a hill(sometimes on moderately flat ground) or if I purposefully disengage the torque converter by pressing the gas. If it's during hard acceleration rpms can slightly drop from 3k rpms to 2800rpms or they can drop drastically from 3k rpms to 1500 rpms and then back up. Its a hard enough chug that it makes my serpentine belt squeal. If I accelerate through all the chugging to about 75mph, the service engine light will flash until I let off then it turns off. The only code its throwing is a P0420 that triggers the service engine light but will occasionally go away and then come back whether the chugging is occurring or not. Now sometimes if I start my car and take off it feels like its got a misfire in 2 cylinders(very sluggish, engine doesn't sound good) park it, restart it, and its back to "normal" but chugging still occurs. Sometimes it feels entirely normal, no chugging whatsoever. I do get smoke from underneath the hood, under the exhaust manifold(can be leaking from above and dripping down on the hot exhaust manifold) If my car is running semi normally it either doesn't smoke or very little. If its running terribly it smokes quite a bit. Coolant levels stay the same, but my oil level goes down. I've dealt with bad ICMs, and bad coil packs, but nothing that makes my car run as intermittently as this.

[harofreak00]

I've dealt with bad ICMs, and bad coil packs, but nothing that makes my car run as intermittently as this.

What makes you think this isn't ignition related? I'm 99% sure its just a bad coil or ICM.

[ChippaT]

Anything is possible, but I've gone through 4-5 ICM's in the past 5 years and it's never acted like this plus it threw codes relating to misfires when they did go bad. which I'm not getting right now. Same with coil packs. They usually die on the spot and not intermittently in my experience. Every time a coil pack or ICM has gone bad it developed a sulfur smell. Under normal acceleration 1500-3krpms it runs normally until I get to that 55-65mph range then it starts chugging. I guess the coil pack could be arching under hard acceleration but I'm not sure.

[95naSTA]

Have you replaced your spark plug wires recently?

[ChippaT]

I'll pick up some coil packs when I'm on lunch and I'll report back my findings.

[ChippaT]

It's been probably a year or so since I've replaced spark plug/spark plug wires, but about 3 months ago I had a coil pack go out and I tested all the spark plug wires for continuity with and ohm meter bending them in all different shapes and it never broke continuity which led me to test the coil packs and find out that was the issue. The wires seem to be in good condition with no cracks to be seen.

[ChippaT]

I swapped the coil packs and it ran 10 times worse. Bad enough I had to limp it home and put in the old coil packs to get it driving again.

[harofreak00]

A new ICM every year is not normal. You're probably getting junk parts.

Read this: https://www.bendbulletin.com/business/b ... d5920.html

I suggest a brand new OE ICM & Coils

[samples08]

I dont see any mention about changing Plugs when is the last time you changed plugs and what type are you using.