Thread: Help! Multiple cyilnder miss fire

So, here is my problem...A few day's ago I started the car up in the morning and it acted up. Idle was erratic with the engine seeming to surge, and the lights on dash and head lights would dim when the rpms dropped but brighten when the engine surged and rpms raised. This only lasted a minute and car ran normally after I put it in drive and drove away. Side note: I don't know if this makes a difference but the day before this happened I had a new starter installed. Moving on...A couple days after the morning incident my husband took the car somewhere, he returned 15 min later saying there was something wrong with the car. It was bucking and fighting him on the highway. He said it was bucking and whinding and having great difficulty getting up to highway speeds. The funny part is no CEL ever came on...I scanned it anyway and it gave codes for miss fire on all 6 cylinders. I drove the car 20 min later after hubby came back and got codes and the car ran fine, around town and highway. And I drove it for a good hour. The problem seems intermittent...And the no CEL coming on is cause for concern. I'm stumped. Only thing wrong with car is a coolant leak coming from upper intake, and mysterious ABS issues that seem to be pointing to a connector around control arm. Only recent work done has been new battery, re-built tranny, egr valve, new starter, new belt and the car had computer re-flashed before tranny work was done. So, all cylinders miss fire with no CEL coming on. Any clues?

I'd be looking at the icm, maybe replace it with a known good one just to test if you know any other 3800ers. Or like 15 bucks at pullaparts. And on the codes was it the p0300 for random multiple misfires or was it the actual cylinders setting thier own codes? (p0301, p0302 etc...)

I got a bonneville recently too with same symptoms and it turned out to be dirty clogged injectors. I took them all out and scrubbed them down with a toothbrush, then made a jig to hook them to my compressor and run cleaner through them and the thing purred like a kitten. But with your random problem of it working fine then not I would still be looking more at the ignition control module. Cause injectors don't unclog and re clog themselves in a matter of minutes or days in my experience.

Could be many different things, I'd like to think it's the weather change we've had recently or a little condensation in the fuel. Both are pretty common for us New Englanders.

Is it becoming any more consistent?

Found out....And it isn't pretty....

I've got a coolant leak inside the body which would explain why it has become more of a problem on the highway. Makes me cringe to know all that coolant was being forced into the cylinders and wreaking havoc, And you all know that blows..Glad it was caught now and not after the engine seized up. And the engine light did finally come on, flashing like crazy. That's when I knew it was time to go right to the shop and have it torn apart. She'll be fixed this week

Thankx for all the suggestions guy's....only wish it had been one of them.

Upper intake gasket is a piece of cake.. fix it

Originally Posted by kfish

doubt its the upper intake gasket. i bet the coolant ports are ****ed on the manifold itself. the plastic ones are known to do this. thats why the aluminum one is more desirable.

Ding, Ding, Ding!!! we have a winnah!! You are correct. I wouldn't care if were just a gasket.

All fixed. New manifold....Happy Day

Rockauto sells the manifold for $85. It's actually a quick easy fix. I've done this job in the parts store parking lot.