muneebk

I've started having some odd issues with my '94 C4. A few weeks ago I noticed she started hesitating a bit on the highway, but it seemed to go away. A little later it started again, this time worse when I had the ac compressor running. Then last week i started seeing the yellow ABS light and red differential lights come on and off randomly (but together) while the engine started bouncing all over the place. The tach started jumping. I shut off the ac but it still persisted. This morning without the AC on at all it started happening and the power started cycling to the car. Even the 12V AUX flickered because the presets on the radio disappeared. The wing also refused to go back down when I stopped. I checked the fuse box earlier and didnt see anthing there (both boxes). I checked the ground strap off the battery and it looked fine. I tightened both the chassis and battery sides to be sure, but no cigar. At first I though maybe an alternator issue, but the battery would buffer any short term alternator hiccups. Any ideas?

Computamedic

This sounds like the classic symptoms of HT leakage through bad coils/distributor caps and/or HT leads. Leakimg HT current plays havoc with the electronics and fires off all manner of faults. You should be able to see evidence of leakage on the surface of the coil caps and inside the distributor caps.

Regards

Dave

muneebk

Pardon my ignorance, but what should the leakage look like?

Uber 911

Park your car up in a very dark place, leave it running and open the engine lid. if the HT leads and coil packs are shot you'll have your own little lightening display under there. If not, check the distributor caps for signs of carbon deposits, your looking for thin black lines.

muneebk

Thanks guys. I'll give it a try tonight. Of course I have to pick this month to move so I cant find my scantool anywhere. Figures. Hopefully its not the ignition wires. ~$800 for those babies!!!!! That is a crime.

muneebk

So this past weekend I replaced my caps and rotors. First off the dealer wanted $480 for the set!! I called around after looking online and got them from a local auto parts store (same exact Bosch parts) for $150. That is just robbery. Anyways, after pulling them off I noticed that all the terminals looked great except one. It was the center ignition coil terminal that was all corroded. That should have tipped me off. After putting it all together the car was doing the same thing so pulled over to the side of the road during my test drive I went to grab the plug for that terminal and got a healthy dose of some few thousand volts. My arm still hurts. So that put the nail in the coffin. Its clearly the wire. I hate to spend over $500 bucks for a full new set when they are only 25K miles old. Maybe I'll call some salvage yards to see what I can dig up.
Thanks again guys for all the help. I would never have guessed it was a HIgh Voltage problem.

Anybody got an extra coil to top (physical) distributor cap wire lying around they wanna sell?


--moe

dfinnegan

Have you tried putting dielectric grease in the ends of the wires before putting them on the caps? I had a xmas tree light show one night and used the dielectric grease and haven't had the issue since.

Note that there seems to be some debate about whether to use this stuff, or not. But, if you are looking at spending the $500 this might be an option worth trying.

Cheers,
Dave

newsboy

Did you check in the dark for stray voltage. You can mist with some water to enhance. To check this on the coils, you would have to take the coil covers off. I know you got shocked, and this could be causing your problem. I have found that coils that show NO stray voltage, and test within Porsche specs, can still have internal problems . You can replace both for around $100.00.

dcbailey

I've had the same symptoms with my car for the past year: Xmas tree effect, backfire when cold, hesitant throttle response, etc. I replaced both coils this past weekend while Hurricane Ike went by, and was amazed by the difference in power that I'm getting. It's purring like a kitten now!

Here's a link to a DIY for replacing the coils with pictures: https://rennlist.com/forums/964-forum/375433-what-effect-to-coils-have-on-power.html . It took me about an hour to do, and wasn't that difficult (even though there looks to be little room for your hand). Adding on to the DIY, I wouldn't remove the top middle Allen bolt; just loosen the bottom middle one through the access hole, then look around the fuse box (easiest to take off the cover), and you will notice another Allen bolt, not mentioned in the DIY, that is the key one to remove. Removing one will allow the closest coil to be removed with some careful positioning. Note that my old coils (original ones, I think) were a bit stuck to the clamp.

The change in the car is remarkable, btw.

It's all done mostly by feel, though you can see the Allen bolts if you look carefully.

muneebk

So after what seems like an eternity of time and attempts at swapping out parts I was able to get around to replacing the coils this past weekend. One of the two coils I received had a hairline crack in the plastic top so unfortunately I had to pay to have another sent next day air Saturday delivery (more $ than the coil itself, oh well.) I'm happy to report that after about 3 hours of driving my "Christmas tree" problem and other weird electrical issues have disappeared. After removing the fuse box and rear-blower tube the swap was pretty simple and I didnt even drop the damn allen bolt into the engine bay.

Maybe its my imagination, but the car definitely seems smoother and more powerful. Come to think of it I think it looks better too! Thanks again to all those who helped me pin this one down. I'm sorry it took me so long to get around to fixing it. Now I have an extra used CCU that I'll need to get rid of.

--thanks!

elbeee964

That's not your imagination -- both: true.

(These gems sparkle when everything's righteous.)

muneebk

So it appears I spoke (typed) too soon. After 3 days of driving (~8 hours) the car started hesitating a little then progressively got worse to the point that the "Christmas Tree Effect" is back in full force. It definitely gets worse when I turn the temp **** off of "blue" and start that rear blower motor. So far I've changed:
1) Caps and Rotors
2) DME Relay
3) Ignition coil wires
4) Coils themselves.

I've been avoiding changing the wires for the $$ and quite frankly I'm afraid of removing all the things I need to get to the lower plugs. I'm a novice at this and after looking at those Cat bolts, or more importantly the rust on them, I'm weary of my novice skills.
Would it be possible to unplug one Coil igniter (sp?) at a time to see if I can narrow down which set of wires might be the issue? I'm assuming the car will run with just one set of plugs, and that I wont do any damage disabling one coil, no? Is there anything else I can check like ground straps (anybody have any pictures of where they might be?)
Oh well. Those were a nice 3 days of clean running. I feel like I own a Jaguar.

--moe

muneebk

At the risk of looking like I'm bumping this thread I forgot to mention that it seems that the longer the car sits the longer it seems to run the next time without issues. Weird.

Computamedic

Your brief mention of the rear blower caught my eye and given that electrical interference is a well known cause of the Christmas Tree effect I wonder if an experiment to disconnect the rear blower (or remove it's fuse) would be worthwhile to do before taking more drastic action.

It's not inconceivable that the rear blower, as it warms up, could induce some interference into the electronics that may be the source of your problem. This may explain the delay you mention above in that it may take longer for the blower to get to that stage if it's been idle for an extended period. It's a cheap experiment so maybe worth a try.

Dave

muneebk

Thanks Dave. I'll give that a try tonight. My game-plan will be to try removing the Rear Blower fuse first, then try unplugging one igniter at a time, then finally to try and swap out the CCU with another one that I have lying around to see if any of those make a difference. I also have to try to find a spray bottle lying around to give the arc-show a chance.