grounding distributor
 

does anyone have a suggestion of how to check the grounding of the distributor. i would like to run a wire directly from the distributor to the negative post of the battery. Car is 12 volt negative ground. thanks hope everyone is staying safe. good time to quartine in the barn and work on the A.

Re: grounding distributor
 

Am curious as to why you feel the need to do this since the distributor is well grounded mechanically at multiple places. Simple cleaning/freshening of dist. mechanical grounding including the Battery grounding cable on both ends, is all that is needed.
I am unaware of a good way to measure other than closing the points with ignition on, and measuring DC volts across the closed points to battery ground, should be extremely close to 0.0 volts DC. Just do not leave the points closed for long as it will heat up the coil.


Hope you do not mind the second guessing, but are you having some symptoms?

Re: grounding distributor
 

May want to check if all paint is removed between distrib and head contact faces. Do you have access to a continuity tester or multimeter to check ground path from distrib housing to a stud on engine, etc ?

Re: grounding distributor
 

Other distributor grounding places should be clean/free of paint, the tabs on the upper plate and distributor body channels for the upper plate are bare/make good contact, clean/no paint


I am not a believer in Wireless plates due to experience. Others have not had an issue. The version I had the wireless connection was mechanical and moved every time the spark adjust was used. After a short while the contact was poor causing odd issues. Went back to original plate and have not had any problems since.

Re: grounding distributor
 

Continuity/ohms check is OK. I prefer to use voltage if possible when checking for continuity, less chance of lead and probe contact resistance affecting readings, when trying to measure very low ohms.




Just my personal preference.

Re: grounding distributor
 

don't mind the second guessing. While driving (After short distance, still cool) it will backfire one maybe two times then runs fine for various times (30 sec to 4-5 minutes) then back fired again. have checked the fuel lines, the carburetor.

The car did this a year ago and went thru the electrical system in cluding changing the wiring harnesses, coil, distributor. Not sure which cured the problem but it quit. ran for over 6 months and many miles ok. Then it started again.

Thought the dist might be losing ground temporaily.
should have included this in my original posting.
any help is appreciated.

Re: grounding distributor
 

thats the reason, i wanted to check with a one wire ground to see if i might prove that is the problem. have been through all the connecting points that might be the issue. See response to 30 closed cap for the issue i am having. Thanks any help is appreciated.

Re: grounding distributor
 

Yes. The plate, base for points should be ground is that correct.
Thanks

Re: grounding distributor
 

When you say backfire, is it extremely loud like a shotgun, or more a hesitation/quiet pop/cough?

Here is a bunch of ideas/checks.

Wiring, was the ignition cable replaced or bypassed? Sometimes the internal wires deteriorate and can intermittently short to the metal casing.
Have you tried replacing or bypassing the ignition switch?
Check/insulate the back of the ignition switch contacts to make sure they are not intermittently shorting to the gas tank.
If you have a starter mounted fuse holder/fuse, the fuse holder can get intermittent. Contact rivets loosen.

Make sure the ammeter nuts are cleaned and are not loose.
Remove and inspect the Wiring Block on the firewall, inspect all is good/tight/clean and no possibility of shorting to the firewall and wiring leads to each other.

Inspect wiring for damage/breaks especially where wiring goes through the fire Wall, insure all grommets are installed (probably already done since you replaced the wiring).

Are your plug reads OK?
Have you checked the carb/intake manifold and intake manifold for leaks?

Re: grounding distributor
 

Yes, on original design points/plates the points block and upper plate are grounded by the upper plate where its tabs ride in the distributor body channels. Also teh spring between teh upper and lower plates.

Re: grounding distributor
 

Here is my criteria for checking the ground resistance of the distributor. I strive to get the resistance of the ground path to 2 Ohms or less.

Re: grounding distributor
 

One other ting you can try. In a very dark place, run it in neutral with the hood open. Look for arcing when it backfires. you may have sneak path. Not sure this would cause a backfire, usually more of a miss or idle issue. Some times the distributor cap gets a resistive path to ground, have also heard that spark plug leads too close to the cap also can cause issues.

Re: grounding distributor
 

If you must try this. Pull the dist, clean the bottom plug that goes into the hole in the block (clean it also), take a piece of wire you're going to the batt with, strip it back about an inch, lay it across the hole in the block, insert the dist. Remove the dist locking bolt and clean it, re-install.
FWIW
Paul in CT

Re: grounding distributor
 

The wire between the upper and lower plates carries the power from the coil up to the point arm. The lower plate is screwed directly to the distributor body, yes but the piece where the armored cable contacts is insulated.


The ground path for the points in the distributor would be the upper plate through the tabs/spring between the plates.

Re: grounding distributor
 

Thanks Ryan for the education, have corrected posts 4 and 10. After reading your post, thinking about it, and looking at my spare distributor I did not know what I thought I knew:)

Re: grounding distributor
 

Pull out you fuel line to the carb, I assume it’s a Zeinth, and make sure the end of the fuel line is not going in too far and hitting the filter screen. The ferrule should be right at the end of the tube.

Re: grounding distributor
 

FSI ignitions, uses a ground wire to make sure the electronic module has a good ground. The ground wire bolts to the upper plate and routes through their supplied armored cable and must attached to a good ground point in the car.
You can try something like that if you want a solid ground for the distributor plate.

Re: grounding distributor
 

I would suspect the ignition switch before I would suspect the distributor grounding. The distributor has a lot of opportunities to have a good ground, even with a "normal" amount of surface rust in some places.

Re: grounding distributor
 

After reading back, it looks like you worked on everything but the ignition switch. I agree with Bill. The cheaper ignition switches are a known issue and original popouts can also get finicky.

Re: grounding distributor
 

KL, does your distributor have the ground clip that attaches to the head bolt and the ignition cable? If not, it should.