Did I just fix my car????

Wrecked944 · 10-08-2005, 12:41 PM

It seems unlikely so I have to ask. Basically, my 964 has been hard to start and often stalls in the rain. I considered replacing the cap and ignition wires. But before I had a chance, it rained today in New England and the car became essentially undrivable. It stalls whenever the tach goes below 4000 rpms. So I searched Pelican and read about "carbon" buildup inside distributor caps and figured it could not hurt to look inside mine. So I pulled just one of my two caps, lightly sanded the rotor and electrical contacts, and then looked for carbon. The inside of the cap was uncracked and bone dry so I figured it had to be this mysterious carbon. Well, I found the smallest little black lines going between the copper points - more like light smudges than lines. And I wiped them away with my finger. I replaced the cap and VROOOM, the car fired up and idled with no problems.

So here is my question: Is this possible? When they say "carbon" inside a distributor cao, is it really just that tiny black smudge between the copper bits that makes the car cough and die? The car starts so easily and idles so well I am tempted to go for a test drive...but it is hard to believe I fixed the problem with a bit of sandpaper and a wipe of my finger. Can it be so?

silverc4s · silverc4s's Garage

Janus,
More likely the wipe of your finger did more than sanding the contacts.

When the spark signal "arcs" from one contact to another, it will leave a carbon trail on the insulating material.

That carbon has a much lower resistance than the insulator, so the next arc is easire than the last, and leaves even more carbon, and so on, and so on...

i would say that you should clean the inside of the caps thoroughly with denatured alcohol, or something similar that will leave no residue of any kind.

Then without touching the inner part of the cap (oils from your hands will also conduct better than the cap material) put it all back together and it should be as good as it will get with these caps.

The worst case is when there are "micro" cracks in the phenoilc cap material, and the carbon gets in there and creates paths for the voltage that cannot be easily elimanated..

PS: GO TEXAS ! ! !

Wrecked944 · 10-08-2005, 02:03 PM

THANKS! I will be sure to do that when it stops raining. I took the car for a test drive and it didn't even hint at stalling. It is still down on power and misfired a few times. But it runs better now than it did in the dry weather. So when the rain stops, I'll do the alcohol cleaning to both distributor caps.

I'm pretty amazed by this. Hard to imagine a tiny black smudge can cause so much trouble!

Nine9six · Nine9six's Garage

What is the mileage on your car? You may want to think about new cap, rotor, and wires, depending on the mileage on the existing units.
If over 50K, I would replace.

klaucke · 10-08-2005, 02:34 PM

You got the CV issue sorted out?

silverc4s · silverc4s's Garage

Janus,
If you look inside the cap with a very bright light, you should be able to see any carbon tracks, or cracks containing carbon.

Yes carbon is what they make resistors out of commonly, it conducts electricity, NOT like copper, etc. metals - but better than insulators, and we are talking 1000's of volts here, so that's all it takes.

Hugh R · 10-08-2005, 05:25 PM

35 years ago in High School automechanics one of the favorite ways of screwing with another student trying to diagnosis an engine idle/running problem was to take a #2 lead pencil and scribble with it inside a distributor cap. Very few students figured it out.

Wrecked944 · 10-09-2005, 11:44 AM

Quote:

Originally posted by klaucke
You got the CV issue sorted out?

I just updated the CV thread to report that BOLT OUT fixed the problem. And it was easy. Very nice tool.

Anyway, I tried to start the 911 today in the rain and it fired up and idled with no problems. But then after driving maybe a quarter mile it stalled and resumed is previous bad behavior exactly as before. It took me forever to baby it back home again. So I am baffled. Might as well replace the distributor caps I guess since the car hasn't had a proper tune up in a few years anyway. Aside from that I suppose I could hope for good weather?

HarryD · 10-09-2005, 01:02 PM

Janus,

Car does not run when wet. Hmmmmm. Could be your wires are not insulating properly. How to tell? With your car in a dark place, start it and look in your engine compartment. Do you see a light show? If so, your wires are bad and will need replacement. If not, spray lightly with water and see if they arc.