Internal distibutor block high resistance

[wesk]

Just got this question in a PM from wrprc and I feel all should benefit from it's discussion.

[wesk]

The first question that comes to my mind is what range setting is he using on his VOM or is his VOM auto ranging?

2nd question is are contacts corroded or burned?
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

[wrprc]

Thanks for the quick reply.
My meter was on auto ranging and the contacts do not appear to be burned or corroded. I'm not sure if this makes any difference but but I've had the Jeep since the late '70s (sitting idle the majority that time) and the distributor cap hasn't been replaced since I've had it. Before I toss the cap (unnecessarily?), I'm curious if something closer to zero ohms is recommended for optimum ignition system performance? Having one measurement that's 3 time greater than the other 3 does seem odd even if "some" resistance is normal. I'm hoping that someone who may have a M38A1 dist cap sitting on the shelf will be wiling to share their resistance test results for comparison?

[RonD2]

Given that the engine runs fine and there's no abnormal appearance about the cap, --- I think I'd suspect the meter.

Do you have a another meter to compare with?
Might use an analog meter if you have one.

5,000 and 15,000 ohms is a ton of resistance for simple electrical contacts to have.

Welcome to the forum, first post!
Good luck!
_________________
Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari

[wrprc]

RonD2,

Thanks for the reply. I'm fairly confident in the meter and the readings. I've had a long career of working with avionics and associated test equipment but even so I'm going to take your suggestion and try another meter (analog) to rule it out.

My first thought was that the resistance should be essentially 0 ohms, but since I don't know much beyond the basics of ignitions systems, I'm keeping an open mind about what's considered normal or not.

This is my first post, however for years I've relied on the amazing wealth of knowledge and advice that is so generously shared on this site. It's gotten me past a number of pot holes on the road to getting my Jeep back on that road. (It's almost there. I hope).

[RonD2]

I agree the resistance from any top contact to the corresponding bottom contact (straight through) should be near zero ohms.

Besides the high resistance you measured, I also see no logical reason why one of the four contacts would read differently than the other three.

I assume the cap is clean (sprayed with contact cleaner to remove carbon and dirt) and carefully inspected for cracks or other defects.
(The engine running good seems to eliminate this possibility.)

I don't have a 24 volt system or cap to check for you, but from what I know about distributor caps of any type --- there should be no resistance.

Caps can fail in odd ways (even intermittently) so maybe the best bet is to buy a quality replacement to compare with.

Keep us posted what you find.
Good luck!
_________________
Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari

[wesk]

The resistance on two caps I had on the shelf was between 2 and 4.5 ohms each post. I've checked the Tm 9-1825 and it offers no basic figure to work with. As Ron said I find that outlandish reading extremely odd. Again you did not comment on my question about corrosion and burned contacts.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

[wrprc]

Thanks for the help RonD2 and WesK.

I think you've definitely confirmed that my distributor cap is at least degraded. (FYI - I did confirm similar resistance readings using an analog meter and after recleaning the contact surfaces.) I guess I can't complain about replacing a part that's probably over 50 yrs old. Thanks again for the help with this question and the others that I've had but never posted about.