Coilpack problem?

[oharris]

My '97 Mountaineer started having a strange problem today. It would cut out for a few seconds, no power, backfiring and the tach would drop to almost zero. Then after a few seconds (anywhere from 5 to about 30) it would come back and run normally. The check engine light never turned on, so I'm thinking it is an ignition problem. The pulgs and wires have been recently replaced, so I'm thinking it's the coil pack. Does that sound right?

Thanks in advance.

 

[Tbars4]

..What exactly were you doing when this happened?

..Perhaps you were in a turn, hit a bump, romped the gas or was switching the a/c?

..It sounds more like you have a wire grounding out rather than a coil pack and something that needs to be found sooner rather than later..

 

[oharris]

No, it didn't have anything to do with bumps or the A/C. (the A/C is out right now, so it wasn't even on.) It did this several times. One time I was stopped at a light and when I went to go it did it. It fact now that you mention it, every time it happened was prior to stopping at a light or taking off from a light. It didn't happen at all on the highway.

 

[Tbars4]

..The places I would check first is the new plug wires and electrical in their area and also if your SPV (Solenoid Purge Valve) is located up by the battery box..

..With the motor off check for nicks, burns, etc. but also see if any of these wires could hit metal while swinging forward or reverse upon takeoff and stopping..Make sure you haven't pulled another components wires to tight or something is now dangling...

..Electrical shorts are hard to test or track if you can't reproduce them on command..When you can, you already found your problem..

..I had the SPV wire hitting and grounding on the edge of the stock battery tray and would only do so when I was stopping on a right curve which cut all power (short direct to computer)...Drove me nuts till I found it and some black tape cured it immediately..

 

[oharris]

I got to working on this again, and now its behavior has changed. Before it started up when it was hot out and the engine was warmed up and running. Now it seems to malfunction when the engine is cold, and once it warms up it runs fine. I have looked for shorts and wiggled wires both with it running good and running poorly. I can't get it to make any difference.

One thing I did try is putting a timing light on each wire. The spark seems to be intermittent on certain cylinders, even when it's running right. I tried cleaning the contacts on the plugs that go into the coil packs and again it didn't seem to make any difference.

One suggestion I got was that since it seems to malfunction when it's cold that maybe I have a temperature sensor that is bad.

 

[oharris]

I'm still struggling with this. I have a wrecked but running '97 Explorer 5.0 so I started swapping parts. Swapped the crank trigger, made no difference; swapped the coil packs, made no difference; swapped the computer and so far it's working. I've thought I had it before so the jury is still out on if this is it.

One concern is the numbers on the computer don't match. The mountaineer had SLL4 and the Explorer has XDT2. Is this a problem? It seems to run just fine.

 

[oharris]

Did some more research on this. The Mercury has the 6-54G calibration and the Explorer has the 7-54G calibration. Not sure what the difference is, but it doesn't appear to be the right part. Am I going to do any damage by driving it with the wrong calibration? I am just trying to determine if the problem is the ECM or somewhere else for the moment.

 

[oharris]

Drove it yesterday and no problems at all. The computer isn't throwing any codes, so I guess the mismatched calibration isn't hurting anything.

 

[Turdle]

You might have"fixed" it during the action of connecting the "new" pcm. The problem all along could have been a loose PCM connection. Just throwing this out there. I would throw the old PCM back in there to see if the problem comes back.

 

[oharris]

You might have"fixed" it during the action of connecting the "new" pcm. The problem all along could have been a loose PCM connection. Just throwing this out there. I would throw the old PCM back in there to see if the problem comes back.

Good point, I will try that.

 

[oharris]

Final Report

After two weeks of driving it with the other computer it ran beautifully. I did discover one other problem though, if I would try and downshift the transmission to 2nd, it would do it for a moment then just freewheel. If I tried it with the OD off, it wouldn't even do it for a moment, just freewheeling. The transmission worked just fine before so this was a new problem. So, I did as Turdle suggested and swapped the old computer back in. The runability problem immediately returned. I took it for a drive (once it started running well enough to do so anyway) and now it will downshift with or without the OD button depressed.

So it would seem my problem is indeed the computer, but I'm going to have to get another one since apparently the spare I have doesn't play well with my transmission.

Thanks all for your help!