Coil Pack Problem

[DSMboostin15]

As the title states, I'm having what appears to be a coil pack problem.

Background: It started last week after I was driving for about an hour. It was running great and I went to meet a friend for some food. Went out back to start my '91 TSI afterwards and it sounded like it was running on 2 cylinders. I let the car sit for about 1.5 hours and it started up and ran just fine. Since my friend is also knowledgable with DSMs, he figured that it was probably the coil pack going out. It hasn't happened since until yesterday.

Yesterday, the same thing happened. So today I decided to take some resistance measurements of the coil - both the primary and secondary resistances are within spec (primary - ~0.9 ohms, secondary - ~13.5 kilo-ohms) at ambient conditions (~68*F).

I decided to heat them with a heat gun for 10 minutes, taking measurements every minute, and noticed that the resistance increased to ~16.7 kilo-ohms on coils 1-4 and 2-3. This makes sense since resistance increases due to temperature increases. I also did the test the same time on a "known" good coil pack, and the results were about the same (~16.3 kilo-ohms)

So my question is how high will the coil's resistance go to due to temperature and at what resistance is too high to maintain proper ignition?

Side note: The spark plugs (Bosch Copper equivalents to BPR6ES) are new and gapped at 0.028". The wires are relatively new, but could probably stand to be replaced (NGK). I haven't measured the Power Transistor yet, but will test that next.

Any help or insight to what is going on will be appreciated.

 

[1995gsx20g]

the most common issue with our coil packs isnt broken wires, its worn away insulation.

try spraying your coil with water while its running. (ps it looks really cool at night)

 

[luv2rallye]

Now apply heat to PT while running to test them.

Also know that occasionally a bad coil can partially short internally or not produce enough output voltage with heat or age yet the resistance will show ok (example: internal oil composition breaks down). Only real way to test this is substitution (unless you have an oscilloscope with a 50k volt probe).

You also may have a heat sensitive CAS or ECU.

 

[DSMboostin15]

It could be the CAS. The ECU is a remaned from Motoguy's but it's from my '90. I swapped pins 6 & 14 and it runs great but I'm leary on running it for an extended period.

I've swapped out my coils with that set of "known good" coils, but I'll have to play the waiting game to see if the problem comes back. If it does, I'll try and get a Link log to see what's actually going on.

I'll check the CAS to see if thats within spec.




EDIT: So the coil packs are changed out and the problem happened again. I tested the resistance and it was at 16 kilo-ohms. The next step is to check the Power Transistor.

 

[mtchll]

Hey DSMboostin15, I was just searching around for some kind of info and found your guys posts. I have been having the same exact problem as you, and yet the shop I took my car to is still trying to narrow it down to the ECU being bad, and I have already replaced the ECU and it had the same problem. I really dont think it is the ECU. I have a feeling it might be the coilpack or the PT. Was the PT the actual problem and did replacing it fix everything?? Any help on this would be great!!

 

[DSMboostin15]

Well when I swapped out the coil pack, the problem came back a few days later. Since then, I've swapped out the PT and have yet to see the problem. It only seems to appear when it's really hot out, corresponding to increased under hood temps. It's not supposed to be hot hear until later in the week. I'll report back then for an update.

 

[mtchll]

okay cool thanks . yeah the shop said my ecu was fried, so i got them a new ecu. they had to change my waterpump/timing belt too. after that they started it up and the same problem occured, and theyre still relating it to the ecu because theres power going in but no output power from the ecu. so im hoping there was a fluke with the ecu.

 

[mtchll]

power transistor was the problem

 

[DSMboostin15]

Well that's good to hear that your problem is solved, mine however is not. It sounds like the engine is dropping spark on a cylinder because you can smell the fuel being dumped in. Could this have anything to do with me running a '90 ECU in the '91?

The ECU itself is a re-manned from Motoguy's. The only reason I'm running it is it's socketed and running Link. Are there any values that I can log when the problem happens that would help determine the problem?

 

[And_44]

You found out what was up with your beast I'm having similar trouble.