Perplexing Car Problem Solved!!!

Frank, well done, glad its solved. I have seen faulty rotor arms cause big problems before. However, there is a big lesson here for your mates. Do not go on a wild replacement spree. one thing at a time and check properly first. You posted that the car had been on an oscilloscope. If the mechanic had checked the peak voltage attained when a plug wire was pulled he would have quickly found a high tension leak. Finding the cause shouldn't have taken long. I agree the symptoms must have seemed bizarre but simple tests on a scope could have had him started in 15 minutes. Change the mechanic! Good luck to all, Richard.

We did check the voltages on two different scopes and it checked out, I imagine this was more current related which is not as easy to check for high voltage.

Frank, absolutely not, tracking and tension leak is voltage related. The resistance of the leak would have to be less than the correct route ie the rotor arm to distributor cap gap, the plug leads and the spark plug gap otherwise it wouldn't take it. A non leaking circuit would show a markedly different High tension and primary circuit trace on an oscilliscope than a leaked circuit which would necessarily show a lower peak voltage than normal. Richard.

Thanks for getting back to us frank. Glad it's fixed.

I've been there and done that. There's nothing that can cause more frustration than buying and installing a new part that's bad.

I hope that you guys applied a sufficient quantity of dielectric grease this time to prevent the arc-over. It's also good to put about the seal of the cap and the spark plug covers to keep them from arcing to ground.

Wish I'd seen this post earlier before you paid a kings ransom in parts.

Couldn't disagree more with the last poster. Clean all high tension wires and components scrupulously. Around the coil nose and inside the cap and rotor arm etc and leave it at that. I always used to use brake cleaner and an air line to clean these components and it was done to every car that came in for service. Grease, damp proofing etc, just leads to dust and dirt collection; the next voltage leak route. We are lucky nowadays that so many of these components have been eliminated from the ignition train.

I couldn't agree with you more, people get way over zealous with the dielectric grease and then wonder why after 2500 miles on their last tune up, their car lacks power or it starts missing. My Golden Rule with distributors with rotor caps, is to look in the shaft bore for signs of grounding. I use to make a lot of money rebuilding GM HEI distributors from people not changing the rotor caps or using inferior rotors and seizing the inter-shafts. $75.00 for 1/2 hr of work that included R & R, that was over 30 years ago and people were thrilled to pay it, too.

"consider this education about the nuts & bolts of the forum,"

Hey, while you are sprouting the rules and regulations covering forum use here, could you please cover the section that deals with no name, no backbone posters that don't have the eggs to write some made up name here.

see #6

No, not that one, the one about the no name...............

I'd give you 2 GA's if I could! I usually don't give Anonymous Poster's much merit or credibility, it seems that they're either to embarrassed about what their posting or they don't want people to know what fools they can be. I was going to post this as an AP, but I'd rather own up to it.

Thanks for the support!

Starting a new thread worked out well for me. I had stopped checking the original, because the posts were becoming redundant and boring.

I don't understand what the big deal is.

Congrats on getting that beast working. I just thought of something. I had an ignition problem and it was a lttle different in that the cables were arcing across, but I looked at it as someone cranked the car over in the dark. I'll bet you have seen the unusual arcing within the rotor cap and narrowed it down a lot quicker. Again glad you got it working. Sounds like you now have a good story to tell at the local bar.

We did crank it over in the dark, since the rotor is inside the cap and the ark was going through the plastic of the rotor to its center there was no arc to be seen.

Congratulations on the final solution to your friend's Audi problem. The distributer was always the main suspect and people are always surprised at how 'sneaky' high- voltage can be in finding a weak path to earth. I made a Scorpio electronic ignition system a few years ago and put too many turns on the transformer. As a result I had sparks jumping from the top of the coil to the car chassis and had to scrap the project as it was too dangerous to use!

See, I told you the crankshaft was bent.

Seriously, I am glad you solved the problem, and even more pleased that you took the time to reply to those of us that were trying to solve the problem. Just another thing. The early GM HEI distributors were very prone to burning through rotors. I never heard of it from Audi.

I suspect the bad rotor has a resistor cast into it, and that resistor failed. The voltage could not pass through the resistor, so it found another path.

It does have a 1K resistor cast into it, although I am not sure this was the point of failure although it is possible. A digital multimeter reading showed the resistor to be 1K as it should be. The failure seemed to be that the plastic must of had an unseen crack or void and a carbon trail in the center that allowed the spark to jump to the metal shaft it sits on.

1. Originally the carbon resistor in the rotor was for radio intererence control.

2. Was given a little-used 1955 Buick that had not seen more than 30 MPH in 10 years. On the way home it gave out one backfire and slowed to a stop. Found the remains of the resistor spread around the inside of the distributor cap. Long walk to Auto Parts Store. Had never seen a resisitor in rotor before ( 1970s .)

3. Was given early Honda Civic CVCC by family who had given up in disgust at not being able to keep it running, and when running was difficult to control engine.

I took to Honda Specialty shop, paid dearly for tune-up which they claimed was all it needed. Few thousand miles later, back to same deal. Took to another Honda Shop who did and said the same thing. Same deal, few thousand miles and behavior was back. Finally, I took a look at it myself .

Turned out that the worn rotor conductor across the top was too short and left a larger than designed gap between rotor and individual distributor contacts to wires.

Total resistance was excessive! With a tune-up, spark plug gaps were at their minimum and there was just enough spark to do the job. As plugs wore, gap increased and eventually the gap was too much for the total system. Became hard to start and behaved badly under load. New rotor solved the problem for years.

(This engine was pretty fussy overall. First one to pass California Smog standards without a Catalytic Converter.)

Any good tune-up shop should have spotted the TOTAL RESISTANCE issue. Why they had not been changing the rotor, I don't understand

Thanks for letting us know the cause. One to add to the memory bank. I would not have considered the rotor, given it was new. In future i will keep all old parts so i can go back to the beginning if the new ones don't work.

Cheers,

Jim