M38 Fire problem

cknight · Post by **cknight** » Wed Jun 20, 2007 6:11 pm

Seems it is back at it again. Just to recap. Rebuilt engine, started jeep , it ran great. Parked it for the winter. Worked in the early spring for two weeks, it finally started and it ran poorly for about two minutes and than died. Never started again. Tried about two weeks ago. First thing I did was check for fire and had it. Could not get the jeep to start. Tried for serveral days and checked fire again, no fire. Replaced coil with a coil from Midwest. It started instantly and ran well. Over the next few days it started running poorly again. Tonight I tried to check voltage to batteries after it started and could not get it to start. Will not start, no fire.

Question other than whats wrong?

Could the voltage regulator not be working and frying the coil?

24V old style bread box regulatior

cknight · Post by **cknight** » Wed Jun 20, 2007 7:20 pm

More information.

I have 24.5 volts on the wire going into the coil, 0 on the wire going from coil to points.

Resistance shown on the volt is very high. On my digital meter with the scale set at 200, it shows 155.05

OKCM38CDN · Post by **OKCM38CDN** » Wed Jun 20, 2007 7:36 pm

Coil is open, you should have something going to the points...

cknight · Post by **cknight** » Wed Jun 20, 2007 8:26 pm

24.5 v on wire into the coil
24.5 v on brass spot between terminals
0 wire to points

Post by **wesk** » Wed Jun 20, 2007 9:58 pm

I asume the 24.5 you are measuring is with the engine not running. With the engine running you should have 27.5 to 28.0 volts at the distributor leading. If your voltage regulator is overcharging say in the 30 to 32 volt range it can cook your coil but you need to get measurements with it running.

Do you have the two vent tubes connected to the distributor and are they venting it correctly?

maeserik · Post by **maeserik** » Thu Jun 21, 2007 1:24 am

simply test :

With ignition on, and distr.cap removed, you can close the open contacts with a screwdriver on the contacts. You will see a little spark, if so the coil would be in good condition. When i did have no sparks it was always the condensor wich was bad. The vent.lines are important the coil gets very hot without them.

on this forum were more posts about coil problems, make a search !

Erik

cknight · Post by **cknight** » Thu Jun 21, 2007 6:41 am

Wes, Yes this is with the engine not running. It will not start. No voltage to points, not spark at plugs while cranking the engine. I do have the vent lines hooked up and there is good suction at the pickup tube in the crossover pipe. The total run time on this coil has been around five minutes it 4-5 starts. I was going to check system voltage when I got home yesterday and it would not start.

I do have a question on the vent system. Right now I do not have the restricting valve installed where ithe line from the dist. connects at the tee near the carb. Can this be purchased or made? Where could one purchase it? How would one make it?

maeserik, I am assuming the spark would occur when you arc the screwdriver across the points. This should confirm voltage at the points. I have checked with a volt meter, I have no voltage to the points, no sparking at points when arcing with screwdriver.

I am assuming the coil is cooked and will try to order another today. This one came from midwest. I read another post some time ago that there was alot of cheep china made coils out there and to get a US made, I think it said to get one for the M38A1 or M151. Any thoughts on this?

When I get it started again, can I disconect the cable from the gen. to the reg. until I am ready to test the charging system?

maeserik · Post by **maeserik** » Thu Jun 21, 2007 7:16 am

with the mechanical original regulator it can not be a problem

with the solidstate regulator i thinck you can damage the inside electronic parts

Erik

Post by **wesk** » Thu Jun 21, 2007 8:17 am

If you have a 24 volt charger or an extra pair of 12 volt batteries then disconnect the distributor power lead and supply power to it from either of the aforementioned external sources. Don't forget to provide both a plus and minus connection at the distributor. Now fire her up with no risk of overvoltage to the coil and measure your generator output. Remember to only leave the external source connected while running. Disconnect immediately after shut down. If you leave it connected and the points stop in the closed position you will burn up another coil.

As Erik mentioned you should replace the condenser whenever installing new points of coil. Especially considering todays high prices on the coils.

The referenced coils would be the later type used in the M151's.

cknight · Post by **cknight** » Thu Jun 21, 2007 2:45 pm

Let me see if I understand. The starter will operate on the main set of batteries but the fire for the ignition will be comming from the extra set of batteries. This will allow me have plenty of time to check the system out without risk of cooking the coil.

I will have to run a ground from the second set of batteries to the coil to complete the circuit. Where should I connect this ground to? Could I just not connect it to the motor or any good ground on the jeep?

Post by **wesk** » Thu Jun 21, 2007 8:12 pm

You'll only need 16 gage wire and yes ground the second set of batteries to the distributor housing. One of the copper vent lines to it will work.