spiderw31 Posted February 2, 2008 Report Share Posted February 2, 2008 Ok, so after replacing the ICM last week I was able to get my car to run again, but I still have a bit of an issue. Once off idle (and even once in a while at idle), the car has a random stumble/misfire startign at around 1500RPM under light throttle loads. The stumble is barely noticable until the TCC locks at cruise speeds, and then it is VERY apparent. Every couple of seconds, the car jerks and hesitates quite obviously... VERY annoying, and I'm sure it isn't helping the fuel economy either. Along with the ICM, I changed my plugs and wires (as they were the originals), so I just pulled and inspected them just now to ensure that they were not the cause of the issue. All the plugs look good, no fouling, and they are all gapped properly. So for the next step, I grabbed my timing light and checked each cylinder. I found that the 1-4 pair was the only pair that was consistently firing; both the 2-5 and the 3-6 pairs showed random stumbles once I started opening the throttle. So my question is this: does it sound as though the ICM I got was DOA? I got the GP Sorensen brand, as I didn't feel like paying a bit more than twice as much for the AC Delco... should I have just spent the extra money on the Delco part? Quote Link to comment Share on other sites More sharing options...
ManicMechanic Posted February 3, 2008 Report Share Posted February 3, 2008 Coils going bad? Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted February 3, 2008 Author Report Share Posted February 3, 2008 I doubt it since I didn't have the problem before changing the ICM, and it seems odd that two would die at the exact same time. Probably should check them though... Quote Link to comment Share on other sites More sharing options...
rockfangd Posted February 3, 2008 Report Share Posted February 3, 2008 check your plug wires Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted February 4, 2008 Author Report Share Posted February 4, 2008 check your plug wires Brand new, and I don't see any issue with them or the plugs after the one week I've been running them... Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted February 4, 2008 Author Report Share Posted February 4, 2008 Really what I'm wondering is if anyone has seen an ICM fail with these symptoms, or is it possible that it is the ECM? Is there any way that I could test to see if it is the ECM instead of the ICM? I really need to get a repair manual for this thing... I have one for my other cars, and without it I feel like I'm blind here Quote Link to comment Share on other sites More sharing options...
SigEpCutlass Posted February 4, 2008 Report Share Posted February 4, 2008 Check your coils. If the coils check out okay, your next move should be to test the resistance on the injectors. If the injectors have less than 12 ohms of resistance they are out of spec. Quote Link to comment Share on other sites More sharing options...
charged 3.1 Posted February 4, 2008 Report Share Posted February 4, 2008 How i check gm ecu's is i plug in my BDM and look at the prom id #. If it bad the # jumps around and if its good then the # stays the same. I've also had 2 coils go bad on me just out of the blue too. Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted February 4, 2008 Author Report Share Posted February 4, 2008 I've also had 2 coils go bad on me just out of the blue too. Correct me if I'm wrong, but all three coil packs are identical, right? If so, then I could swap the position of two coils and see if the problem follows the coil. Quote Link to comment Share on other sites More sharing options...
mfewtrail Posted February 5, 2008 Report Share Posted February 5, 2008 I've also had 2 coils go bad on me just out of the blue too. Correct me if I'm wrong, but all three coil packs are identical, right? If so, then I could swap the position of two coils and see if the problem follows the coil. Yes, all the coil packs are identical. For what it's worth, I've never seen an ICM fail and give you the problems you've described. All the ICM failures I've experienced resulted in stalling when warm and eventually a no-start condition(due to no spark) when the module completely failed. I've installed several aftermarket ICM's and never had a problem with any of them by the way. Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted February 5, 2008 Author Report Share Posted February 5, 2008 Yes, all the coil packs are identical. For what it's worth, I've never seen an ICM fail and give you the problems you've described... Thanks, I thought they were... I'll swap coils and see what happens. Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted February 17, 2008 Author Report Share Posted February 17, 2008 OK, I'm at a loss here... Swapped coils in, and it made no difference, so I exchanged the ICM. The new one behaves EXACTLY the same, with the stumble at cruise RPMs. I've double checked my plugs and they look great and are gapped correctly. I swapped in a known good MAP I had laying around just for kicks, and no change (didn't really expect anything though). The ONLY other thing I can think of right now are the plug wires I just put on when I initially changed the ICM, but they don't appear to be bad (no light show, everything is solid), or that I really should just spring for the AC Delco ICM and be done with it. Any thoughts? Quote Link to comment Share on other sites More sharing options...
88red4cyl Posted February 17, 2008 Report Share Posted February 17, 2008 It really doesn't sound like an ICM to me.. I got the symptoms mfewtrail described when the ICM went bad on my Fiero.. I had a condition similar to yours, except mine was worse and the car was backfiring horrendously under load over like 1000 rpms. I changed out the plugs and wires and the problem went away.. Quote Link to comment Share on other sites More sharing options...
ns87 Posted February 17, 2008 Report Share Posted February 17, 2008 Check to see that all the wires are firmly clicked on the coil packs/ plugs. I would check the fuel filter/ fuel pump. Having had a fuel pump die, as well as coil packs/ bad plugs I can tell the difference between the stumbles. Here are my observations: Fuel related stumble feels like the car is cutting in and out really fast. Ex: Giving it gas, and stuttering to get there. Spark related stumble feels more like a jolt. The engine physically jumps up and down a bit. You can feel it. Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted February 18, 2008 Author Report Share Posted February 18, 2008 Spark related stumble feels more like a jolt. The engine physically jumps up and down a bit. You can feel it. That is exactly what it feels like, but only at low RPMs; if I gun it, it runs hard and fast up the the 6k shift point. I'm also sure it is spark, as I have put a timing light on each individual wire and I can actually see each cylinder randomly not firing; there is a quick hiccup in the stobe action of the light. Also checked the fuel pressure when initially diagnosing the earlier no start, and then rechecked later. I've got 40psi, key in ignition position and motor off, and I get 42-44psi at idle, so the pump is good. I've double and triple checked the connections at each plug boot and at the coil packs as well, so I know they are on fully, although they don't seem to take all that much force to clip in. The wires are brand new, and I also was sure to use the exact factory wire routing as well. The wires are Autolites... anyone ever have issues with those? Dunno if this is relevant or not, but I seem to remember reading a rumor somewhere that the 3.4 really should run premium... is this true? Quote Link to comment Share on other sites More sharing options...
ns87 Posted February 18, 2008 Report Share Posted February 18, 2008 I'm using auto lites with No problem. I've never heard of 3.4 using premium and running better. I think your last two options really are O2 sensor and defective plug wires/plugs. Every so often things are defective right out the box. I had a wire set where one wire would not SNAP onto the coil post. I had a misfire and had to return it. If nothing changes after you replace the O2 sensor, I would yank the plugs/wires and exchange them. If that doesn't work! Check the wiring around the ICM. See if any of the wires are frayed, melted, etc. Also maybe grab a JY computer. Someone should chime in whether that computer controls the spark timing. Quote Link to comment Share on other sites More sharing options...
z34Phoenix Posted February 18, 2008 Report Share Posted February 18, 2008 i would even say check the TPS sensor. if you swapped the coil packs around and the problem didnt move that elimiates the coil packs.... which leaves the plugs, wires and ICM and fuel injectors. Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted February 28, 2008 Author Report Share Posted February 28, 2008 UPDATE: I got really tired of chasing my tail on this problem, so I took it into the shop to see if they could find it. This shop is an excellent shop, extremely knowledgable, they've been around for quite some time with an ecellent reputation; one of the best shops I've seen in a long time. All that said, they couldn't pin the problem down either! They've verified there are no sensor dropouts, all signals are good, all connections are solid as it the wiring. Plugs are fine as are the wires, fuel pressure and injectors are good. They also changed the fuel filter, looked at the TPS, checked for vacuum leaks, basically going over everything they could think of with a fine tooth comb, and found nothing. In fact, they were so intrigued by the issue, they started checking and testing things on their own time and were releuctant to give the car back, as they really wanted to find the issue! My last trick is to put in an AC Delco ICM and see if that cures it finally. I'll be picking the parts up today, so we'll see what happens shortly. On the upside, I'm getting very good at swapping ICMs fast now! Quote Link to comment Share on other sites More sharing options...
IRONDOG442 Posted February 28, 2008 Report Share Posted February 28, 2008 Good luck on that one, that always blows my mind when shops are blown away and want to keep working on the car to solve the problem. Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted February 29, 2008 Author Report Share Posted February 29, 2008 Good luck on that one, that always blows my mind when shops are blown away and want to keep working on the car to solve the problem. Thanks... at this rate I need all the luck I can get... Wife picked up the Delco ICM, and when I got home and looked at it, it was obviously a used part! Took it back to Advance, and they are ordering yet another... it'll be here Saturday. This is getting rediculous... Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted March 3, 2008 Author Report Share Posted March 3, 2008 Got the Delco ICM installed, and the problem is still there but maybe slightly diminished. Also changed the TPS, and while it definately made the throttle response a LOT smoother, it did nothing for the stumbling issue. At this point, I'm confident the electronics are fine, and I've verified fuel delivery. Considering that I changed plugs and wires at the same time as the ICM originally, I'll bet it is one of those. Of those, I'm gonna guess wires. Any recommended brands to go with on wires? Right now I'm thinking Delco on those too... Quote Link to comment Share on other sites More sharing options...
Chancho Posted March 3, 2008 Report Share Posted March 3, 2008 random note but hook the car up to a vac gauge and see if the car may have a vac leak, slow vac leaks anywhere will give you somewhat of the same hesitation feel Quote Link to comment Share on other sites More sharing options...
rockfangd Posted March 3, 2008 Report Share Posted March 3, 2008 i had the same problem on my 94 cutlass. the wires were visibly perfect but i had an aweful stumble upon acceleration. I finally figured out it was the wires after a few months of going nuts trying to find the problem. So i went with delco wires and delco platinum plugs. it runs perfect. The best of luck to you Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted March 3, 2008 Author Report Share Posted March 3, 2008 random note but hook the car up to a vac gauge and see if the car may have a vac leak, slow vac leaks anywhere will give you somewhat of the same hesitation feel No vac leaks; the shop checked that when they were trying to sort it out. i had the same problem on my 94 cutlass. the wires were visibly perfect but i had an aweful stumble upon acceleration. I finally figured out it was the wires after a few months of going nuts trying to find the problem. So i went with delco wires and delco platinum plugs. it runs perfect. The best of luck to you Delco wires it is then! The platinums work well? I've heard bad things about them when used on a waste spark system like we have on these cars, so I've got the standard Delco resistor plugs in there. Quote Link to comment Share on other sites More sharing options...
GM Guy Posted March 19, 2008 Report Share Posted March 19, 2008 Any update? Been having a similar problem periodically w/ my 95 GP 3100, 206k and still doesn't burn oil, had it since new. Feels like the engine fires on 3 cyl for a few secs or will drop in RPM for a sec like fuel was cut off, doesn't matter which gear, seems to be more apparent in 4th OD since the TQ is engaged so when it jerks its that much more noticeable. Replaced plugs/wires followed by TPS, both crank sensors, all coil packs and the ICM, checked and double checked the wiring harnesses but no change. Strange thing is that it only seems to happen around 70 degrees and above which means it is happening quite a bit now being I am in FL. I also have a throttle delay occasionally which led me to the TPS but the replacement didn't make a difference. Did all the other typical servicing including EGR passage, injector cleaning, throttle body, etc. Had a bud years ago with a 93 GP and his EGR would carbon up after 10-15k and would cause all kinds of stalling/hesitation issues. Haven't had a chance to test fuel pressure, pump has never been replaced. Anyone else out there with any ideas? Could it be the PCM overheating or just going bad? Can happen within 1-2 min of driving. Anyone know how much dealers charge to flash a PCM? Had a ton of wierd stuff happen w/ my 88 Corsica, PCM would overheat and the engine would die till it sat turned off for a few min. Ironically the PCM was the cheapest thing to replace on that car. This is an awesome site, been here for a while but first posting. Quote Link to comment Share on other sites More sharing options...
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