regal 1-4 coil problem

Hello-
I have a 1992 Buick Regal with the 3.1 (vin T) engine. It idles ok in park, though there is a slight irregular vibration. When shifted into drive/reverse this vibration is much more exaggerated. This problem first started after I started up the car, after lunch. The car had been working fine to that point.

When I got home I found that the sparkplug wire on cyl 4 was slightly disconnected from the coil. After snaping it all the way on, I turned on the car and it was idleing fine in park and drive. I drove it around the block and in the middle of my test drive it developed a severe lack of power, it couldnt accelerate much and the trans would upshift/downshift many times in a row on slight inclines. When I got the car back to my house the car was idleing rough, just like before. I found that all the wires were still fully connected to the coils.

I checked the spark on the coils and found that the 1-4 coil was sometimes producing a weak spark if any at all, the other two coils were working fine. I tested my 1-4 coil and found that is is still good(ohms were both correct). I bought a new coil, installed it and it didn't fix anything, so I returned that coil. I took the ignition control module to Autozone and it tested good.

I have tested my sparkplug wires(good), and replaced all sparkplugs. I dont know where to go from here. I have checked the obd I for codes and there are none. The fact that the car does start/idle should indicate a working CKP sensor, right? Any help you can give would be greatly appreciated.

Thank you.

Bad spark plug wires are a common cause of misfire, with or without codes. The wires may be leaking current to ground or other wires, shorting the spark before it can reach the plug. Also, internal resistance may be increased, raising the required firing voltage to the point where the engine may misfire. You said the wires are good, however, did you check resistance of the wires to see if they are within specifications? You may also want to change one coil/wire out with another, to see if the “weak spark” moves with the coil and or wires. Another quick test, would be to check the suspect coil/wires in the dark to see if you have visible signs of arcing. It helps to spray a mist of water in that area, prior to checking.

Low coil output can also be caused by a faulty ignition module or a faulty coil driver circuit inside the PCM. A lot of coils are replaced unnecessarily because problems like these are overlooked or misdiagnosed.

Thanks for the suggestions HotZ28. I have tried swaping the coils and the problem remains in the same 1-4 cylinder spot. The coils all work fine in the two other positions. I swaped the spark plug wires and all of the wires were transmitting the spark. I checked the ohms on each wire and they were well below the spec. of 30000 ohms. I will look for arcing tonight. I have already taken the icm to autozone where it was tested good, could their test be inaccurate. Is there a way to test the pcm for this problem? I just keep thinking it has to be the icm.

-The Chupacabra

A short or low resistance in the coil's secondary windings will result in a weak spark, but will not damage the module or PCM driver circuit. An open or high resistance in the coil's secondary windings will also cause a weak spark, or no spark, and may also damage the ignition module due to feedback induction through the primary circuit. An important point to keep in mind with respect to all types of ignition coils is that when the magnetic field collapses, the high voltage surge has to go somewhere. If it can't go to the spark plug, it will find another path to ground, which may be back through the ignition module, PCM driver circuit or through the insulation inside the coil itself. This can be very damaging to these parts. That would take us back to the original problem you found with the loose ignition wire at the coil 1-4. I am not sure the “Auto Zone” test could detect anything other than a totally malfunctioning ICM. It might be worth a swap with a used unit first, to see if that corrects the problem. This is a a little “shop secret” that you can try to see if the ICM module and the crankshaft sensor circuit are working. Connect a halogen headlamp to the spade terminals that mate the ICM module to the coils. A headlamp is recommended here because it puts more of a load on the module than a test lamp. If the headlamp flashes when the engine is cranked, the ICM module and crankshaft position sensor circuit are functioning.

HotZ28-
Thankyou for all of your suggestions. I looked for leaking spark arc in the dark... No arcing. I hooked a halogen lamp to the two leads on the icm and it did not blink at all. So I finally went to the parts store and picked up a new icm installed it. My car is now running on six cylinders once again... I don't know why the test of the old icm came out good, when the new one seems to have fixed the problem... Oh well, Thanks again HotZ28
-The Chupacabra

Your troubleshooting ability and willingness to resolve the problem, was what gave you success! I wish all people had your dedication and determination, it sure would make "internet troubleshooting" easier! I don't know why the Auto Zone ICM test is unreliable, however, this seems to be quite common. I guess it is like balancing a tire; first you have to have someone that knows what he is doing, and then be willing to do it! Anyway, "I love it when a plan comes together"!:grinyes: