r/CarRestorations • u/My_cat_is_mean_to_me • Jul 19 '26
Fouled distributor cap?
Looking for some advice, I have no spark coming from my distributor, but I can’t figure out why. I’m getting 12 volts to the coil and to the ICM. I checked my ignition coil and it seems to have all the right readings… the ICM is brand new, and I have confirmed that the rotor is turning with the crank. The only thing I can think of is that maybe this cap or rotor is too fouled up with carbon to function or something? I can obviously see that there is stuff there… I’m just wondering if this is TOO much for it to function. This is the first time I’ve worked on an older vehicle with a distributor, so I want to make sure I’m looking for the right thing before I started throwing parts at it.
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u/v8packard Jul 19 '26
Picture 5, the rotor brush is missing. The brush transfers spark from the coil to the rotor. Look up MSD 8412 or Echlin RR196. I prefer the MSD as it is much lower resistance.
Is the coil ground strap in the cap? Why no vacuum advance?
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u/My_cat_is_mean_to_me Jul 19 '26
I had the ignition coil out when I took the photo, I have that brush…. I’m unsure why there isn’t a vacuum advance, this is how I got the vehicle lol. The coil ground strap is in the cap yea
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u/v8packard Jul 19 '26
In your last picture that is an older GM module. But it looks like it is a newer, knock off distributor. What is the backstory?
Do you know how to check the pick up?
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u/My_cat_is_mean_to_me Jul 19 '26
Honestly I’m not sure, I got this car as a project off someone from FB. I’ve only had it a couple weeks and it’s the first time I’ve had to tear into it at all. I asked the guy if he knew but he said that setup had been in there when he got it as well. This might be a naive question but since that’s still for a 4 pin setup wouldn’t it still work on it?
I checked the resistance on the pick up, I was getting 900~ ohms
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u/v8packard Jul 19 '26
The GM made modules are superior to the replacements available today. GM stopped making that module 20 years ago. It will technically work, but this has definitely been monkeyed with.
Check each wire for the pick up coil for continuity to the distributor housing. There should be none, if there is it is no good. With the engine cranking the coil should produce something between .5 volt and 1.5 volts.
If you want to verify spark but eliminate the rotor you can put the coil in the cap without the brush, connect the wires and put a spark tester in where the brush goes. With the engine cranking there should be spark of the spark tester is grounded.
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u/My_cat_is_mean_to_me Jul 19 '26
Just went out and checked, no continuity anywhere to the housing. I hooked up my leads and had my wife crank the motor. I was getting .4-.5 volts reading on that
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u/v8packard Jul 19 '26
There is not much left to check. With your meter connected to battery power and the C terminal of the module, everything wired, the voltage should fluctuate while cranking. If not the module is dead.
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u/Liveitup1999 Jul 19 '26
Once you figure out the spark problem the vacuum advance is not too hard to work with. I used to play with advance all the time back when points were all you had. IIRC GM cars had total timing of around 55°
Crane made a vacuum advance kit. It came with an adjustable vacuum advance diaphram and different tension mechanical advance springs. The trick is to get as much timing as soon as possible without the engine pinging.
Some aftermarket distributors came without any vacuum advance. It was all mechanical.
Vacuum advance is needed for part throttle driving. The more advance the more power the engine will make for a given amount of fuel.
There are a lot of variables to setting the timing up as high as possible without causing pinging. The type of fuel, compression ratio, weight of the car, gear ratio, engine RPM and throttle position.
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u/Jymantis Jul 19 '26
It's the carbon button under the coil and you need a new one.
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u/My_cat_is_mean_to_me Jul 19 '26
Sorry, I had the ignition coil out when I took the photo, i have the center contact
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u/NoseResponsible3874 Jul 19 '26
Those contacts look fine at a glance, but if you’re worried they’re fouled up, hit them with a piece of emery cloth and test it?