COIL BAD?

1950 - 1952, M38, questions, discussions, regarding anything related to the M38.
JMZ421
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COIL BAD?

Post by JMZ421 » Sun Mar 26, 2017 3:44 pm

When my M38 reaches operating temperature, maybe half hour after driving, she starts to have a sputter on acceleration and loses power. This is consistent now. I changed the points and condenser about 400 miles ago, cleaned spark plugs, gapped yesterday and installed NEW wires. I also changed thermostat. She starts right up at cold. The M38 does not overheat. Maintaining proper idle is an issue when this happens also. If 35 MPH down the road seems to run OK providing under load. I do have a spare original coil in a new old stock distributor. Sounds to me like a bad coil starting to worsen. What do you think? This symptom was there before the wire change!! Thanks John


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Re: COIL BAD?

Post by Joe Gopan » Sun Mar 26, 2017 4:23 pm

It will do no harm to try it. When changing coils in the waterproof distributors, be careful to route the primary wires to the coil in a manner that they will not get pinched and shorted. The radio filter capacitor in the power inlet #12 can act up with similar symptom.
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JMZ421
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Re: COIL BAD?

Post by JMZ421 » Mon Mar 27, 2017 9:16 am

Ok, I read about that radio capacitor, very interesting. I will let you know if coil corrects performance problem. My M38 is a later and has that part in the distributor.
Thanks for the info. John

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Re: COIL BAD?

Post by muttguru » Mon Mar 27, 2017 12:59 pm

John,

is it a genuine Milspec coil? If it's a shiny, chrome-bodied coil, there's a whole sage about the problems caused by these faulty repro coils. If you want, I'll post the links to the articles.
Ken
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Re: COIL BAD?

Post by Wolfman » Tue Mar 28, 2017 5:17 am

One more thought.
When is the last time the valves were adjusted ??
Tight valves will do what you describe. Run OK cold. The warmer the engine gets, the worse it runs.
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Re: COIL BAD?

Post by JMZ421 » Tue Mar 28, 2017 11:02 am

I appreciate the responses. I do have a NOS complete distributor that was given to me. Also, I probably should have adjusted those valves when I replaced the intake last year. I wanted to enjoy the M38 and needed it for some parades and so forth. The engine was rebuilt in 1998 but the vehicle has not been used very much at all, not many miles since rebuild. I will try the coil maybe tackle that later. I already Utubed that process. Thanks John

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Re: COIL BAD?

Post by Radtech » Tue Mar 28, 2017 12:27 pm

Make sure the distributor is properly vented from the crossover tube to the distributor then to the T on the vacuum pump for the wipers.My father told me years ago when he worked on these for the Airforce that if it was not properly vented that the coils would get so hot they would burn out.

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Re: COIL BAD?

Post by JMZ421 » Thu Mar 30, 2017 2:24 am

I will check all these suggestions. Thanks John

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Re: COIL BAD?

Post by JMZ421 » Tue Apr 04, 2017 3:17 pm

When adjusting valves, I see on page 112 of the TM, is the bottom wrench only needed to hold the tappet in place so that the top wrench is able to adjust? Once in spec, nothing needs tightned or locked down, correct? This can be done keeping manifolds on, correct again? Are these valves adjusted every 3,000 miles? Thanks for your input John

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Re: COIL BAD?

Post by Joe Gopan » Tue Apr 04, 2017 6:30 pm

I readjust at 500 miles and sort of forget them for the next 40-50K. I do, however, hook up the GI Issue Vacuum Gauge every 10,000 miles or so and check for abnormal readings which also indicate valve condition or function and readjust if necessary.
2011 MVPA PIONEER AWARD - MVPA #1064
HONOR GRAD-WHEELED VEHICLE MECHANIC SCHOOL 1960 - US ARMY ORDNANCE SCHOOL(MACHINIST) ABERDEEN PG 1962 - O-1 BIRD DOG CREWCHIEF - 300,000+TROUBLE FREE M-38A1 MILES
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Re: COIL BAD?

Post by Wolfman » Sat Apr 08, 2017 5:29 am

Correct JM.
Hold the body. Turn the top adjusting screw.
No lock nut. They are or are suppose to be self locking.
Mike Wolford
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Re: COIL BAD?

Post by JMZ421 » Sat Apr 08, 2017 5:51 am

Wolfman, Thank you very much John

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Re: COIL BAD?

Post by Joe Gopan » Sat Apr 08, 2017 6:05 am

Adjust them cold per manual, won't be noisy. We did it both ways in the Army. Leave your fender on, buy new gaskets for cover and ventilator, use copper gaskets on cover bolts.
Most difficult part of job is removing and reinstalling the Valve Cover.
2011 MVPA PIONEER AWARD - MVPA #1064
HONOR GRAD-WHEELED VEHICLE MECHANIC SCHOOL 1960 - US ARMY ORDNANCE SCHOOL(MACHINIST) ABERDEEN PG 1962 - O-1 BIRD DOG CREWCHIEF - 300,000+TROUBLE FREE M-38A1 MILES
LIFE MEMBER AM LEGION-40/8-DAV
7 MIL SPEC MAINTAINED MV'S
COL. BRUNO BROOKS (ARMY MOTORS) IS MY HERO

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Re: COIL BAD?

Post by JMZ421 » Sun Apr 09, 2017 4:54 am

Thank you Ben for the info. Much appreciate all the help John

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Re: COIL BAD?

Post by JMZ421 » Sat May 13, 2017 1:59 pm

Today, I changed the condenser and cap, (had both of them), cleaned the battery ground, replaced the ground strap on the engine to mount. I also replaced the fuel filter with one of the new washable filters. After all this, the M38 was still sputtering when driving for 10 or so minutes and backfiring a little, especially in the start inn first gear. So, since is nice out today, I decided to replace the spark plugs with some old ones I took out over a year ago. I just put autolites in it last summer!! The jeep does not sputter anymore and I drove around for a good half hour. The idle is still an issue but I will check the timing. One of the plugs looked a little different than the rest, maybe that was just a bad plug. Glad I kept those old plugs. Never thought newer plugs would be bad. I will take them out and clean as they were carboned up but I just wanted to see if she would run better. John


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