94 Euro 3.1 misses

Hi all. My wife has a 94 Lumina 3.1, which I cant seem to fix. The problem is it misses upon acceleration, and sometimes misses and runs very rough while idling. There are no codes, and I recently replaced plugs and wires (thought that would fix it) and a possible vacuum leak. No change. I searched the forum and did not come up with my exact problem, and any help would be appreciated. Thanks.

Many things can cause this, dirty injectors, bad coil, bad ign module to name the more common ones.

maxwedge...thanks for replying and giving me some places to start looking. I pulled each plugwire from the coils while the car was idling. #3 didnt change the idle or the sound of the engine when removed. Also, the sparks coming from it were weaker than the other five. I pulled the coil off and took it to Autozone to have them test it. I was told by them that it was weak, but still within specs. They really didnt want to sell me a new one, instead telling me the problem was my control module. So, I took each coil off and cleaned the connecters and put them back on (I also moved the weak coil, the middle one, to the right side) So far, it runs and idles good.

Should I go ahead and replace the weak coil?

Yes I would, if the problem persists have the icm checked.

Well, it got dark on me yesterday, so I tinkered some more this morning. I removed all 3 coils, cleaned the connections, removed and cleaned the control module, then took it and the coils to have them checked. All coils secondary output were low. (5 - 10 normal range, mine were mid 5s and one one 6) Module tested fine. I was told by the guy at Autozone that he cannot do a full test on my coils, but they were within spec. on the secondary output (I think that's what he called it) He's very convinced the problem is water in the gas. I'm not so sure, I poured some water remover in the tank to appease my wife, no change. I must say, after cleaning all of the connections, it runs a lot better, but that miss is still there. It runs great until it warms up. Maybe the module or the coils only act up under heat? This car is driving me crazy, I'm a Jeep guy, GM fwds are new to me.

If you have a definitive misfire at idle kill one cylinder at a time till there is no change in the engine roughness, that is the suspect cylinder.

If you have a definitive misfire at idle kill one cylinder at a time till there is no change in the engine roughness, that is the suspect cylinder.


Just did what you suggested. One cylinder definely not firing. Replaced that coil with a new one for my piece of mind....still misses. Fuel injecter? LOL

If you have spark to that cylinder a known good plug, either the injector is bad or the engine has low compression, see if you can feel or hear the injector clicking, tough to get to these of course.

hmmm, not to be contrary, but you should at least swap the wire going to the misfiring cylinder with another one just to eliminate this possiblity (faulty wire) and cheap fix (a new wire). Swap a pair of plugs too just in case the one is gummed up.

There is also a product like STP ...something-50 that thickens the oil and increases compression. If that fixes it, then you have discovered it really is low compression and/or bad rings for only a few dollars. (and you may tolerate adding something like this to the oil until you can pay to get new rings...)