24 volt coil question

[NAM VET]

You can get a spark plug wire adaptor from our forum vendors for checking your engine rpm and timing, fits on the plug on one end, then connects to the plug wire on the other, allowing use of an inductive timing clamp on the adapter wire, so you can see your RPM, then per usual see the flashing of the timing lite on the pulley timing light at the pointer. Also use a multimeter to see what your plug wire resistance is, I had one bad wire, and got a used plug wire from a vendor and it had good spark then.

My guess is that you have one bad wire, with a broken core somewhere, and your multimeter will show that. If your #1 wire seems good, then perhaps your distributor cap has a crack or carbon trail or broken rotor tip or the like. I actually had a broken and wobbly rotor before a Pertronix was installed by Charles T, and yet my truck still started and ran! Good luck... Hal

[ashyers]

If you've only lost spark in Cyl. 1 the coil is most likely OK.

Here's my suggestion for testing the circuit from the coil to Cyl. 1. Remove the wire from the plug, yank the eraser & sleeve off a pencil, place the dull end of the pencil into the end of the wire and place the pointed end ~ 3/16" from a ground. Turn the truck over. If you don't get a healthy spark that'll jump the gap you know this issue in in the secondary. As far as secondary issues I've had a 3 and one can lead to another!
Issue 1: plug, not firing, high internal resistance
Issue 2: due to the plug not firing the voltage found the next best thing and burnt through the weakest point in the wire
Issue 3: likely linked to issue 1, the voltage blew through one of the towers on the cap

There's some posts on this saga somewhere... I was only getting a miss under high load and it took a while to figure out where the issue was. The pencil made it easy .

Andy

[John Mc]

Quick follow up question to this thread. If my multimeter is only pulling about 10.5K ohms on the secondary does this mean the coil is probably shot? I'm pulling 5.9-6.0 on the primary.

It's definitely not getting a spark at the #1 plug. Hoping by listening to the engine turn over someone might be able to help diagnose I've included a link to my youtube channel of me turning over the engine and videoing the #1 plug wire not sparking:
https://youtube.com/shorts/IbPRx4oMku8?feature=share

Between 5-6 ohms on the primary is normal for NOS coils. Most of the people I've seen reporting measurements report them being at the higher end of that range. I've heard that the spec on the secondary was 11,000 - 15,000 ohms.

For the aftermarket coils, the Chinese chrome-finish coils measure about 11 or 12 ohms on the primary and about 11,000 ohms on the secondary. Peter Debella Jeep had some new coils made up a couple of years ago. He searched for a US manufacturer to make a batch, but none were willing. So his also ended up being made in China, but report are that they are a step up in quality from the chrome coils. His primary resistance was the same as the chrome coils, but the secondary was about 12,000 ohms. Both the chrome and the Debella coils output a lower spark voltage than the NOS coils.

I have no personal experience with the Chrome coils (and I've only owned my M37 for a few years). From what I've read Chrome coils have a reputation for failing. Some of this may be undeserved: It's not clear whether this is really due to the coil itself, or if it's a matter of not having the vent lines to the distributor properly installed and functioning. I've read where some think they don't fit in the distributor properly, and theorize that this can interfere with the ability to transfer heat away from the coil. (Some have tried installing a copper washer/shim under the coil with heat condictive past in an attempt to improve the fit and heat conduction. I don't know whether this actually made a difference or not.)

I've got 3000 miles on my Debella coil (paired with a Pertronix electronic ignition) with zero problems. I've run it in a wide variety of conditions (stop & go traffic, extended 45-50 MPH runs, 90 degree weather, and done some cold weather starts). Since I've never run a NOS coil, I don't really know if that would affect performance at all. I can say I'm happy with how my truck is running now, and the price of the Debella coils is reasonable at $55 plus shipping.

[NAM VET]

My truck recently began to advice a hesitation under load when hot, so thinking it is a failing coil, I tested the three spares I have, one a new chrome one, and two older OEM ones, with were working when removed in the past. All had acceptable Ohm resistance with a digital meter on the + and - terminals, but 0 Ohm readings when testing the center terminal to the - terminal, or in fact, in any of the ways I could test the center terminal. I don't know yet what the coil reads in the mounted distributor yet.

Just got two black ones from DeBella, promptly shipped, $55 each, and they read 12.6 Ohm across the two top terminals, but they also read 0 Ohm when testing the center terminal to the neg or even the pos screw terminals! I have read on this forum and others about how to properly test a coil, and I am doing it correctly. So, assuming the one in my truck is defective, I have now 6 coils all with a failed resistance!

I will call DeBella tomorrow and ask for then to promptly replace the two bad black ones but test them before they send them to me.

Jeeze, what a hassle. We have sold two homes, one in Rock Hill, and the other at Seabrook Island at the coast, and bought a new one being completed in Columbia, so we have a LOT of work to do downsizing two into one, 200 miles apart. I have to get my truck running quickly.

I will post my much loved truck for sale very soon. I have somewhere between $35-40K plus in it, not to mention many many hundreds of my own hours in its restoration. I know selling a restored vehicle is always a loosing proposition.

hal

[John Mc]

That's the first report of a problem with the Debella coils I have heard. That fact that you have multiple coils all showing identical problems makes me wonder. If you had actually installed and run them in your truck and they failed, I'd suspect you have a problem with your truck that was burning them out (such as your ignition remaining on when the truck is not running, burning out coils?). If you are seeing a problem even with never used coils, I'd wonder if you have a problem with your ohm meter - if it has multiple scales, perhaps just one scale has failed? Before giving them up as no good, it might be worth borrowing another Ohm meter to double check.

[NAM VET]

I have. a Pertronix, and with a master battery cutt off, I have never left the ignition on. New plug wires, and will check my readings with another tester, but set on Auto it should pick up whatever resistance is there. I tried other settings. I'll soon get an answer to this. hal

[John Mc]

I'll be interested to hear what you come up with.

I wasn't sure if you had the old style meter where you had to set the range manually. I had one as a teenager with one resistance range blown (probably because I screwed up and tried to measure voltage while set to a resistance range.)

[NAM VET]

well, your suggestion to check my multimeter's range was correct, when I took it off Auto, and set to different ranges, all is good on at least three coils, one old Autometer, a new chrome one, and a DeBella coil, reading 12,000 ohms across the center to the neg and I think 12.6 ohms across the two side terminals. Something like that.

So removed the cap's spark cables, and removed the top of the distributor, and pulled out the chrome one in side, and it actually tested fine too. Then put in a new distributor cap just in case, and had to slightly elongate the DeBella two holes and eventually got the wires back on correctly and the cap back on.

My thighs hurt from pressing against the fender side, and under a 100 degree sun, the lower distributor cap screws were invisible in the sun, plus trying to work on my truck looking thru the top part of my bifocals, set to infinity focus, when the object I need to see is two feet in front of me is just plain hard.

I am a bit overheated, so taking a break before I put the wires back on the distributor cap, and then fire it up. I was very very careful to not drop any small screws or washers down into the distributor.

I sure hope this gets me back on the road running fine. Thanks, hal

[NAM VET]

And I love the smell of burned electrics!! Put it all back together, referring to my pictures I shot before I took my distributor top off, and carefully put the red and green and the little yellow wire precisely where they were supposed to be. Checked, and rechecked. But no ignition!!

Pulled off the dizzy top, getting quicker at that, and sure enough, some how, I had reversed the red and green wires, no matter how carefully I checked my pics of how it was originally installed. I don't know, told my wife it is because I am red-green color blind, but actually, some how, in carefully placing the wires securely under the coil clamp, I flipped them.

So went ahead and pulled the Pertronix out, the coil still reads fine, the capacitor on the Pertronix plate is burned. and will get one ASAP and this time have my wife check my wiring colors. She absolutely hates my truck!

Will report back. hal