Testing an ignition coil - M170

qualityhardware · Post by **qualityhardware** » Fri Nov 24, 2006 11:42 am

Had my M170 running the other day pretty well. Set the timing and tripled checked the condenser points for .020" gap on the high edge of the rotor cam and she ran great...for a day.

I am now not getting spark. Pulled the #1 wire and plug from the block and observed no spark from the plug while cranking.

I pulled the cap from the distributor and observed the condenser points while cranking.

The ignition coil threw a single spark from the positive terminal and the condenser points sparked twice and that was it.

I pulled the primary cable from the coil and grounded it with the ignition switch "on". Got one $&% of a spark - which according to the manual, means the capacitor and cable to the capacitor are A-OK.

Does this mean my coil is bad? If yes, what's the best way to test it?

Thanks...

OKCM38CDN · Post by **OKCM38CDN** » Fri Nov 24, 2006 4:18 pm

Is your coil one of the cheap ones from China maybe...?

I got one of those and it ran for about a day then blew the top off the coil...

I found an older American made one at aswap meet and have not had problems since... Might try John Bizal at Midwest Military or Frank's Surplus in PA... Most any coil for a 24v system should work... look for something from an M151, M-38A1 or such...

Hope this helps...

Post by **wesk** » Fri Nov 24, 2006 10:02 pm

Not sure which manual you are referring to. If you get a good hot spark then your coil is producing. I would take a long hard look at the system trigger. and it's guard. The points and the condenser.

Hook all like it's suppose to be and leave the condenser disconnected and turn rotor to close the points. Now turn on the ignition and with a plastic or wood probe open the points and the coil should produce a spark. If it does you need a new condenser.

qualityhardware · Post by **qualityhardware** » Sat Nov 25, 2006 9:38 am

Thanks Wes,

I am using TM 9-8014 for the M38A1 and M170.

I did as you advised. Popped the top off the distributor and rotated the points until closed.

Turned on the ignition switch and opened the points with a chopstick.

Spark was really weak and intermittent. Every now and then, the (+) terminal on the coil would throw a big spark.

I doubled checked the points gap to .020" and then turned the motor. Got a consistent but weak spark.

As a final check, I put the top back on the distributor and tried cranking - even with a dose of ether in the carb. Nothing. Sounds like the spark is too weak to cause spark at the plugs.

So this would mean I need new condenser points?

Post by **wesk** » Sat Nov 25, 2006 3:50 pm

If you can't get a good spark with or without the condenser connected then it looks like coil replacement time. If you have a digital VOM and can understand the taking of Ohm readings I can supply the test points and the ohm readings for the coil/ Best done with the coil removed from the distributor.

qualityhardware · Post by **qualityhardware** » Sun Nov 26, 2006 12:48 am

Hi Wes,

I appreciate it. Digital VOM and Ohm readings is out of my league. Looks like the coil replacement is where I need to go...

steveh · Post by **steveh** » Thu Dec 07, 2006 5:54 am

I was just reviewing older message and ran across this one. I would be interested in Ohm values for the coil on my M38 - serial number 61702, motor number 72685, distributor number AXS 1851, Ord numbr 7355596, serial number 2F108673.

Thanks

Steve H
Somerset, OH

Post by **wesk** » Thu Dec 07, 2006 8:27 pm

TM 9-1825B Auto-Lite Electrical Equipment manual contains the info. Our coils are CT series.

qualityhardware · Post by **qualityhardware** » Fri Dec 08, 2006 7:23 am

Wes,

YOU ARE THE MAN.

Thanks.

charlesfitton · Post by **charlesfitton** » Wed Jun 01, 2016 3:04 pm

TM9 1825B?

Post by **wesk** » Wed Jun 01, 2016 7:54 pm

Excerpts of this manual as apply to our jeeps are on our downloads page as PDF files.

http://www.willysmjeeps.com/v2/modules. ... oad&cid=46
There are several other locations on our download pages as well.

Since our jeeps left Willys and Kaiser with Autolite electrical components we usually only think of Autolite but the military also contracted Delco Remy to produce components of their own design that met the Mil Spec for 24 volt electrical systems and would interchange with existing Autolite equipment. They have a manual as well.

charlesfitton · Post by **charlesfitton** » Thu Jun 02, 2016 3:59 am

Excellent - I can't find these in the downloads section.

4x4M38 · Post by **4x4M38** » Thu Jun 02, 2016 5:23 am

Hello Charles,
As Wes said, the whole manuals are not there, just excerpts,
under M38, M38A1/electrical:
http://www.willysmjeeps.com/v2/modules. ... eA&show=10

Post by **wesk** » Sat Jun 04, 2016 1:18 pm

Charles just look for the topic you are troubleshooting in the downloads section and you will find them. There are several and they are located under the topic not the name of the manual.