I have a '98 bonneville ssei, and one of the coil packs is not firing at all. I have tested every coil post by plugging a spark plug into it and running the car. 4 of them fire every single time, 2 fire very very infrequently or not at all, and they are on the same pack. I have tried replacing the coil pack, doesn't make a difference. How should I go about troubleshooting this? From my research I have determined that is most likely a loose connection, bad wire somewhere, or bad ICM but I don't really know how to go about figuring it out. Any help would be appreciated. Thanks! is the check engine lite on?
even tho u replaced the coil, did u try swapping it with one of the good ones to see if the problem 'moves' to diffrent cylinders with the coil? how about swapping plugs and wires?
another thing u can do is disconnect the wiring connector from the module and make sure the terminals are in good shape and making good contact. check the connector for loose or backed out terminals. follow the wires back as far as u can and check for breaks, wore off insulation, etc.
the problem with these modules is that there aint a good way to test them without special equipment. usualy what we do is eliminate evrything else, and replace the module if all else fails. conniecartech wrote:is the check engine lite on?
even tho u replaced the coil, did u try swapping it with one of the good ones to see if the problem 'moves' to diffrent cylinders with the coil? how about swapping plugs and wires?
another thing u can do is disconnect the wiring connector from the module and make sure the terminals are in good shape and making good contact. check the connector for loose or backed out terminals. follow the wires back as far as u can and check for breaks, wore off insulation, etc.
the problem with these modules is that there aint a good way to test them without special equipment. usualy what we do is eliminate evrything else, and replace the module if all else fails.
Ya the engine light is on, I have a reader and it has confirmed cylinders are misfiring. Obviously since there is no spark they are not firing.
My method of testing each coil/post was using the same spark plug wire plugged into the same post, so that everything is the same except which post I am using. The problem does not move, it is definitely just the one coil pack. I did try with a couple different wires and plugs, always the same results. It fires every time one 4 of the posts, not at all on the 2 bad ones.
I took a quick look at the big connector for all the coils by disconnecting it... I didn't notice anything obviously wrong. I followed the wires as far back as I could.. It looks like smoeone of them go to the computer which I assume is the signal to spark, and one that went down to the bottom of the car and plugged into something, which I think might be the ground? I would bet there is a chance something is bad there, because we recently did work in that area and something could have been damaged or not plugged in all the way.
I couldn't really see anything on the ICM (Which I assume is the big computer thing that a whole bunch of wires plug into... and I think is what you mean when you say 'module'?), because I took the cover off it but all the actual connections are inside of it. And hopefully it didn't go bad because I think that is expensive to fix... though maybe I would just grab a junkyard one well, first lets get our jargon on the same page.
when i said 'module' i meant the icm, or ignition control module. thats where the flat 14 wire connector plugs into, and the coils sit on top of it. what your calling the computer is the pcm, or powertrain control module. and your right, the pcm commands the coils to fire.
the 'wire going to the bottom' sounds like the connection to the crankshaft position sensor. this tells the pcm when #1 cylinder is at top dead center. if the pcm knows that, it knows when to fire each plug at the proper time. it wouldnt hurt to check that connector, but i doubt that the crank sensor is the problem, if it was bad it would cause problems on all the cylinders, not just 2.
its starting to sound like the problem is either the icm or pcm. icm's fail a lot more then pcm's cause they take a lot of heat from the engine. and this configuration has been a problem on gm engines for years. but the only way to rule out a pcm would be to hook up a high end scantool that displays live data and see whats going on with the pcm. but if u held a gun to my head
id go with the icm. unless u wanna take it to a competant shop and get it checked out. conniecartech wrote:well, first lets get our jargon on the same page.
when i said 'module' i meant the icm, or ignition control module. thats where the flat 14 wire connector plugs into, and the coils sit on top of it. what your calling the computer is the pcm, or powertrain control module. and your right, the pcm commands the coils to fire.
the 'wire going to the bottom' sounds like the connection to the crankshaft position sensor. this tells the pcm when #1 cylinder is at top dead center. if the pcm knows that, it knows when to fire each plug at the proper time. it wouldnt hurt to check that connector, but i doubt that the crank sensor is the problem, if it was bad it would cause problems on all the cylinders, not just 2.
its starting to sound like the problem is either the icm or pcm. icm's fail a lot more then pcm's cause they take a lot of heat from the engine. and this configuration has been a problem on gm engines for years. but the only way to rule out a pcm would be to hook up a high end scantool that displays live data and see whats going on with the pcm. but if u held a gun to my head
id go with the icm. unless u wanna take it to a competant shop and get it checked out.
I have an OBDII sensor that hooks up to my laptop, and I actually can get real time data. I don't know what I would want to look at though to find out if it is the pcm though. And is the ICM really small then? Because i looked under the coils and there was was a small, flat metal box thing right under them, but that was it. If that is all it is then it doesn't sound like it will be all that difficult to replace! not sure if your tool will do it, but check to see if the pcm is commanding all the coils to fire. the icm is pretty easy to replace on this one, just pull the coils off and unplug the 14 wire connector, then remove the mounting bolts.
If you swapped coils around and you still don't have spark, it needs an ICM. One of the coil drivers (transistors) in the ICM is bad. Your getting crank reference, power, and ground to the ICM or else the engine wouldn't start. You'll still get spark if the bypass goes bad to the PCM, so the PCM won't cause a no spark on one coil. The PCM only controls ignition timing once the engine's RPM is high enough by grounding the bypass circuit and switching timing control over through the EST circuit. During cranking, low rpms under 400 rpm, or EST faults the circuitry inside the ICM controls the firing of the coils. discretesignals wrote:If you swapped coils around and you still don't have spark, it needs an ICM. One of the coil drivers (transistors) in the ICM is bad. Your getting crank reference, power, and ground to the ICM or else the engine wouldn't start. You'll still get spark if the bypass goes bad to the PCM, so the PCM won't cause a no spark on one coil. The PCM only controls ignition timing once the engine's RPM is high enough by grounding the bypass circuit and switching timing control over through the EST circuit. During cranking, low rpms under 400 rpm, or EST faults the circuitry inside the ICM controls the firing of the coils.
Hmm that is interesting to me... Because even though it was firing improperly at idle, My car shows by far the biggest problems at medium rpms or higher. I was just asking about this specific problem because, hey, it was an obvious one. When I go to higher rpms it has a lot of trouble and the car has no power... I mean it sounds like i will have to replace the ICM either way, but could my PCM be what is causing my car trouble at higher rpms? I think it has to be either a sensor somewhere or the computer, every other source of ignition has been checked... There might still be some partially clogged injectors but I don't know if that would cause my massive lack of power and god-awful fuel economy One last thing... I actually have the wires for each coil plugged in reverse order. IE, instead of 145236, it is 412563. Why do I have it that way? Because if I have it the *correct* way, the car runs EXTREMELY poorly. it idles okay... but any gas and it either dies or has an extremely tough time overall. I have asked about this in other forums and nobody has been able to explain it... If somebody understood that whole system enough to explain it, I might be able to pinpoint the source of my problem. I read a complicated explanation of how an ignition control system works, and I found one important piece of information. I thought that the spark that goes out through each post on the same coil was exactly the same. It turns out they are not... The current goes a different direction because the polarity never changes. On one post the current goes out, and on the other the current comes in. But again, if everything was working perfectly, it shouldn't MATTER whether it goes out or in for a given spark plug and thus it should run exactly the same if you switch posts. But it doesn't... Who can figure out why?
Here is the information I read:
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