euro1990 Posted October 12, 2003 Report Share Posted October 12, 2003 I've been trying to diagnose this for quite some time... 90 Lumina, 205k miles on it. Randomly I lose 2 cylinders at a time. Some days I'll go out, fire it up... running perfect on all 6. Other mornings, runs real shaky and is obviously only firing on 4 cylinders. Sometimes attempt to move the car under such condition, it'll go down to 2 cylinders. I've tried 2 different ignition modules (both used junkyard parts, came out of cars with less than 100k miles on em) and swapped various coil packs in and out, but the problem remains the same. Since it continues to be random and seems to work perfect sometimes and crappy other times with these different combinations of parts, I'm pretty reluctant to go buy a new module or new coils. SO... anyone know of what else in the ignition system could create such a condition? Last night I drove the car all over the place, ran just fine. This morning, went out and fired up... running on 4. Thanks for any advice guys! Quote Link to comment Share on other sites More sharing options...
Bolt_Crank Posted October 12, 2003 Report Share Posted October 12, 2003 have you tried changing the plugs and plug wires? and your fuel filter too.... Quote Link to comment Share on other sites More sharing options...
Redfox340 Posted October 12, 2003 Report Share Posted October 12, 2003 If you know for a fact it's down on 2 cylinders, it's a faulty coil. But, a faulty Crank Position sensor can give you the same results / problems. Double check spark / resistance on all 6 cylinders and try to isolate the problem. - Erik Quote Link to comment Share on other sites More sharing options...
Robby1870 Posted October 12, 2003 Report Share Posted October 12, 2003 Yeah, if you have tried different ICMs and coils and its still there, and its random, it sounds like the Crank Sensor. Erik beat me to it Quote Link to comment Share on other sites More sharing options...
euro1990 Posted October 12, 2003 Author Report Share Posted October 12, 2003 THanks for the advice guys... Wires and plugs are relatively new, gave the wires a look, all look good. I did the crank sensor about 5 years ago or so, but hey, sounds more likely than coils or module at this point in the game. Thanks again go Cubs!!! Quote Link to comment Share on other sites More sharing options...
euro1990 Posted October 14, 2003 Author Report Share Posted October 14, 2003 so the mystery continues... Well, without checking the spark, I went ahead and replaced the crank sensor. Made zero difference. Started looking at the spark, noticed that the spark on #6 looked kinda weak (in comparison to 2 or 4). So I replace that coil. Made no difference. Replaced that wire. Made a small difference (in noticeable spark, but not in terms of the car running better). I was pulling plug wires one by one (including the back 3) checking for spark. When pulling each wire, I noticed that on cylinders 2 and 6, it really made no difference in performance when I pulled the wire off. With all other 4 cylinders, when I pulled the wire away, it ran even worse. 2 and 6... no difference whatsoever. I checked those plugs, all looked fine, even went so far as to replace one just to be sure... made no difference. I didn't do a compression check, but that's really all I have left. I have between 30 - 40 psi fuel pressure, and plenty of unburned fuel is coming out of the exhaust. My guess is maybe a stuck valve? If it is, I sure am glad it's on the front cylinder head. My only other idea was timing... perhaps for some reason 2 and 6 are firing at the completely wrong time? What controls the timing? ECU? DIS? Tempted to try ignition module #4 (which would involve me going to get another one from the junkyard) since when I last replaced it, the car ran fine that evening. What else in the system could cause a DIS to fail? Well, lemme know your opinions... This Lumina is about 1 or 2 repair attempts away from being donated to charity as a tax writeoff. Despite my love for my Lumina, I now know why I bought a new car!! Quote Link to comment Share on other sites More sharing options...
Robby1870 Posted October 14, 2003 Report Share Posted October 14, 2003 Try a new Ignition Control Module. You said 2&6, they arent even on the same coil, so definitely try the ICM. Dont think its a stuck valve, you would hear something and it just doesnt happen that much. 2&6 wires should NOT come off the same coil. Maybe you got em wired wrong. 3&6 are on the same coil, 2&5 are on the same coil and 1&4 are on the other Quote Link to comment Share on other sites More sharing options...
euro1990 Posted October 14, 2003 Author Report Share Posted October 14, 2003 so you see my confusion? Yeah, I know which coils are working which cylinders, and I know with 100% certainty that the wires are correct. Like I said before, sometimes the car runs perfectly.... it's the randomness of this damm thing that is killing me. Any idea what might make an ICM fail? I am tempted to get a new one so I know it's 100% good, but if my car is gonna fry it... no way. Guess I'll get a couple at the junkyard this weekend. Quote Link to comment Share on other sites More sharing options...
Robby1870 Posted October 14, 2003 Report Share Posted October 14, 2003 so you see my confusion? Yeah, I know which coils are working which cylinders, and I know with 100% certainty that the wires are correct. Like I said before, sometimes the car runs perfectly.... it's the randomness of this damm thing that is killing me. Any idea what might make an ICM fail? I am tempted to get a new one so I know it's 100% good, but if my car is gonna fry it... no way. Guess I'll get a couple at the junkyard this weekend. Yeah, your problem is definitely weird. Basically old age and heat kills the ICM. Its right under the exhaust manifold, so it gets pretty hot. All the advice I got is to replace the ICM and hope that works. Make sure your crank sensor wire isnt bare and grounding out to the block, I had a problem like that once. Just some thoughts Quote Link to comment Share on other sites More sharing options...
euro1990 Posted October 14, 2003 Author Report Share Posted October 14, 2003 random indeed. I guess I'll do some wiring inspection and try another ICM or 2. I just gotta get this car running well enough to sell it! She's a good ride when she does run right. Trans rebuilt 35k ago, all new head gaskets, valve job, timing chain... hopefully I can get this ignition crap figured out and get some decent cash for her. Pretty much just taking up space in my driveway these days. Quote Link to comment Share on other sites More sharing options...
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