Testing a coil?

[jbjeeps]

Okay guys, a little ignition 101 help please.

I have the coil out of the dist. and on a non-conducting surface. If I touch the pos terminal of the coil w/ the pos lead of my analog ohm meter and the neg terminal with the neg lead of my meter and the needle jumps to 0, does that mean the coil is not good?

Thanks!

[RICKG]

Jack, 24 volt system basics pgs 13-14 in the downloads
gives a pretty good description and drawings of the coil.

[jbjeeps]

Thanks Rick, that's good info and I appreciate you pointing it out. I'm working at learning what I can about the ignition system and that is helpful.

But, I didn't find an answer to my question there.

Anyone?

[RICKG]

Well, i think you're sposed to have continuity thru
the + and - terminals, so if your ohmmeter is
pegging out when you attach the leads i think that's
normal. DISCLAIMER: i'm certainly no expert

[jbjeeps]

Thanks Rick, I'm sure no expert either. I've spent much of the last two days reading forum posts, swapping ignition parts and trying to understand why the A1 will sometimes refuse to start, and then sometimes start but not run for more than about 5 minutes. First I thought it was the points, then I thought it was the coil. But now I'm stumped.

Here's what I know about the coils:

when I put the ohm meter leads to the two posts of the coil the meter goes to zero, when I put the black lead on the neg. coil post and the red on the secondary of the coil the needle goes to about 11,000.

From what I've read, those two readings should indicate that the coil is good.

Can someone confirm that for me?

[wesk]

You must not have read any of my posts.

First of all a digital VOM is needed for best, most reliable and accurate readings. You are looking for 6.2 to 6.5 Ohms across the primary coil. Zero indicates the primary coil is shorted. Infinity or open means the coil has a broken wire. The secondary will ohm out anywhere from 10,000 to 11,000 ohms.

The correct published method for testing the coils is with a coil tester and checking them under a load at a specific voltage and reading amps used.
The ohm tests will offer reasonably accurate assessment of the condition of the coil. Also they should be at least at room temperature. I usually warm the coils up to a higher temp with a heat gun to simulate hot summer coil operating temp and check primary & secondary resistance again.



You should remove the wires from A & B anyway so you can ohm check them to ground for shorts and inspect them..

Other sources of trouble are:

The capacitor noise filter in the +24Volt power receptacle on the side of the distributor can also give you the grief you are experiencing. If you do not have a capacitance tester then temporarily eliminate or bypass it and drive the jeep.

Carefully inspect the full length of each wire inside that distributor for bare spots and shorts.

The condenser can often give the intermittent troubles you are having.

Bad ground from contact points to distributor housing can give you the same grief. This can be caused by corrosion between the contacts and the plate or the plate and the distributor housing. Or the two plate retainers can be loose.

[oilleaker1]

Make sure your vent tubes are open and connected correctly so the coil does not overheat! Great thread, copied this one too! John

[jbjeeps]

You must not have read any of my posts.

Ha! Touche!

Actually, I read so much my brain is still spinning, but I didn't find this. I've copied it and added it to the TM. Thanks!

Through some kind of wizardry, black magic or hokus pokus, the A1 started up and ran last night, with the same ignition parts in it that I've been swapping in and out for the past two days! And it started up and ran this morning too.

I intend to keep driving the A1 in the backcountry, so I want to be able to find and fix these kind of issues on my own. I'm glad it decided to quit running in the garage instead of out in the forest. How's that for good luck! We carry overnight gear whenever we go out, but I prefer not to have to use it!

I still think it was points, maybe I had them gapped too tight, or maybe there was a bad ground as you mentioned.

I'm replacing the $5 analog meter with a good digital meter, adding a timing light to the tool box and either making a spark plug wire jumper from dist. to #1 plug or buying the timing adapter ($45!).

Maybe I need to get satellite internet service so I can access WillysM from anywhere!

Thanks again to Wes, et al, for all the good info!

[wesk]

The Metal Douglas connectors are notorious for shorting out between the wire, the washer and the cap when they are tired and worn out. This occurs intermittently and will drive you nuts.

That radio noise filter is really unnecessary unless you are operating a set of antique tactical radios. It is easily eliminated from the many sources of trouble in the system. If you retain it carry several spares since even NOS out of the box they fail because they have a shelf life limit.






That little bracket on the contacts where you connect the two wires has a tiny nylon insulator that if damaged can cause you tons of grief.



That $45 dollar timing adapter for your spark plug is not much of a bargain when you consider the entire M series harness adapter kit which contains that adapter and 5 others is less than $100.

[jbjeeps]

Great info, thanks!. Printed and added to the TM.

1. The Metal Douglas connectors are notorious for shorting out between the wire, the washer and the cap when they are tired and worn out. This occurs intermittently and will drive you nuts.

2. That radio noise filter is really unnecessary unless you are operating a set of tactical radios. It is easily eliminated from the many sources of trouble in the system. If you retain it carry several spares since even NOS out of the box they fail because they have a shelf life limit.

3. That little bracket on the contacts where you connect the two wires has a tiny nylon insulator that if damaged can cause you tons of grief.

4. That $45 dollar timing adapter for your spark plug is not much of a bargain when you consider the entire M series harness adapter kit which contains that adapter and 5 others is less than $100.

1. Now that you mention it, I did take the #12 wire between the connector and the dist. out , clean both ends, wrap several layers of electrical tape around it to cover some very bad original insulation and replace it.

2. Okay, so when you say "radio noise filter", I think you're referring to the "capacitor" inside the dist. where the #12 wire connects, is that correct? Part #8329784 in the picture and in Ord 9 Snl G-758?

From the picture it looks like you take off the capacitor/filter, retain the cover plate and splice in a wire that goes to pos. terminal on coil, correct?

3. Yeah, that was one of the places I suspected might be causing the trouble. Lesson: take it apart and clean it when servicing points.

4. 10-4 on that! I'm going to try and make a jumper to use. Maybe someday a complete kit will come along.

[wesk]

2. Okay, so when you say "radio noise filter", I think you're referring to the "capacitor" inside the dist. where the #12 wire connects, is that correct? Part #8329784 in the picture and in Ord 9 Snl G-758?

It's part # XA790 in my photo. You chop the exterior shell and wrapped paper off leaving only the front end cap and the core wire. Then solder a new wire about 7" long to the core pin and slip shrink wrap over it and you will never be bothered with intermittent and dead noise filters again.

[jbjeeps]

Got it, thanks!