M38A1 stalls after warming up

[85J]

Hello, I have an M38A1 that my grandfather restored about 20 years ago. It has been stored in a garage for about the last 10-12 years. I'm trying to get it back up and running but have been having some problems with it after it warms up.

The jeep will start and idle fine until it starts to warm up. Once it starts warming up it will only idle if I bump the rpm up to probably 1000-1500. Eventually it will stall out and not run at all, about 5-10 min after startup.
Once it stalls I cannot restart it at all, even with starting fluid. After it cools back down I can start it up again.

What I have already done:
- Replaced 3 out of 4 plug wires
- Cleaned spark plugs
- Replaced points, rotor, and cap
- Cleaned timing advance weights
- Replaced ignition coil. Tested new coil with an ohm meter and is within spec.
- Replaced ignition coil negative and positive wires inside of the distributor
- Bypassed radio noise filter
- re-clocked distributor with the oil pressure pump according to the TMs and forum posts
- Timed distributor. (Idling at around 10-15 degrees advance)(distributor is retarded as much as possible. It is up against the alternator)
- compression test showed all cylinders are good and consistent
- carburetor rebuilt
- fuel filter installed between fuel pump and carburetor
- fuel pump rebuilt
- fuel tank pickup inspected for holes
- has consistent manifold vacuum but it's low. Around 15-17 In Hg
- Inspected the battery wires for damage or corrosion
- has 24 volt distributor

I have tried to troubleshooting the problem but can't figure it out. Hopefully someone with more knowledge than me can help. Thanks

 

[NDT]

Usually I would point you towards carb flooding but the filter you installed should prevent that. I’m assuming you have no black smoke and typical sputtering associated with the float needle getting stuck open and flooding the engine?
Next I would investigate the low vacuum. Try disconnecting and plugging the intake vacuum fitting and see what happens. Maybe spray brake cleaner around the carb gasket to check for vacuum leaks there.
Lastly, the chinese chrome coils are known for being intermittent. What did you use?

 

[85J]

Usually I would point you towards carb flooding but the filter you installed should prevent that. I’m assuming you have no black smoke and typical sputtering associated with the float needle getting stuck open and flooding the engine?
Next I would investigate the low vacuum. Try disconnecting and plugging the intake vacuum fitting and see what happens. Maybe spray brake cleaner around the carb gasket to check for vacuum leaks there.
Lastly, the chinese chrome coils are known for being intermittent. What did you use?

Thanks for the reply.
No black smoke but it does seem to have a small mis at idle.
I took my vacuum reading from the intake manifold fitting right below the carb. That should give the same effect as plugging it, right?
I have checked the carb gasket for leaks with an un-lit propane torch and didn't see any difference.

I got the coil from Kaiser Willys - https://www.kaiserwillys.com/produc...XJEt-hbi1FVaHYM6lbggMD_BM-A2pyOhoCBjYQAvD_BwE

Replacing the old coil, that was not a chrome coil, didn't seem to change the problem at all.

 

[NDT]

Hmm. Suggest you check for spark right after the stall occurs. Need to determine if ignition is to blame.
Also, the ignitor should be positioned as shown in the TM, with the power connector pointing down. I think timing being way off can result in your low vacuum issue. Roll the engine to top dead center on #1 and verify the points are opening and the rotor is pointing to the #1 cable.

 

[85J]

Hmm. Suggest you check for spark right after the stall occurs. Need to determine if ignition is to blame.
Also, the ignitor should be positioned as shown in the TM, with the power connector pointing down. I think timing being way off can result in your low vacuum issue. Roll the engine to top dead center on #1 and verify the points are opening and the rotor is pointing to the #1 cable.

I ran the jeep last night, took some videos, and checked for spark.
I checked spark by grounding the #1 spark plug on the exhaust manifold and it had good spark before and after running.
I have attached a picture of the engine bay to show how the distributor/ignitor is positioned.
When I set the distributor up I set the rotor pointing to the #1 plug wire (around the 7 o clock position) and the points at 20 thousands

Do I need to re-position the oil pump a tooth over to get more swing from the distributor? I installed it per the TM but I can't retard it anymore.

Video of it Idling:

Video of it stalling:

 

[NDT]

I think you have ignition timing issue. You should be able to fully rotate the ignitor from retarded to advanced, the engine will go from struggling to sounding good to struggling. In the video it sounds like it is struggling.

 

[85J]

I think you have ignition timing issue. You should be able to fully rotate the ignitor from retarded to advanced, the engine will go from struggling to sounding good to struggling. In the video it sounds like it is struggling.

I guess I'll have to take the oil pump out and move it over a tooth or two. Then I'll re-time it.

 

[biscuitwhistler37]

I ran the videos in tandem and the engine lopes the same in both until it stalls, I would try advancing the timing a bit before you retard it any further. It may be an air/fuel mix issue as well, when in cold idle the mix is good, after it kicks off cold idle it goes lean, that's what it sounds like to me. Have you used a timing light to verify the marks are correct?

 

[glcaines]

I would suspect that you have a bad coil. Loss of spark after the coil warms up is a classic coil failure. You mentioned that it wouldn't even fire with starting fluid and that is a dead giveaway. Try to find a new U.S. made coil. The Chinese ones are junk.

 

[85J]

I ran the videos in tandem and the engine lopes the same in both until it stalls, I would try advancing the timing a bit before you retard it any further. It may be an air/fuel mix issue as well, when in cold idle the mix is good, after it kicks off cold idle it goes lean, that's what it sounds like to me. Have you used a timing light to verify the marks are correct?

There are no marks or holes in the crank pulley like I thought there should be. I found TDC on the compression stroke and marked the pulley and then used a timing light to time it.
The timing light should be giving me an accurate reading.
I will try advancing the timing and see how it responds. I thought around 8 degrees advance was about where it should be with 87 octane gas?

It seems like it's running towards the rich side based on the smell of the exhaust and when I pulled the #1 plug yesterday it was dark.
I will try resetting the mixture screw after I check out the timing.

I would suspect that you have a bad coil. Loss of spark after the coil warms up is a classic coil failure. You mentioned that it wouldn't even fire with starting fluid and that is a dead giveaway. Try to find a new U.S. made coil. The Chinese ones are junk.

I believe the old coil that I replaced was bad after warming up, because it was losing spark when hot. I tested for spark with the new coil while hot and it was producing consistent spark.

Thank you guys for the help.

 

[biscuitwhistler37]

There are no marks or holes in the crank pulley like I thought there should be. I found TDC on the compression stroke and marked the pulley and then used a timing light to time it.
The timing light should be giving me an accurate reading.
I will try advancing the timing and see how it responds. I thought around 8 degrees advance was about where it should be with 87 octane gas?

It seems like it's running towards the rich side based on the smell of the exhaust and when I pulled the #1 plug yesterday it was dark.
I will try resetting the mixture screw after I check out the timing.



I believe the old coil that I replaced was bad after warming up, because it was losing spark when hot. I tested for spark with the new coil while hot and it was producing consistent spark.

Thank you guys for the help.

Hmmm.... I'm sure you know but usually when an engine runs rich you get the smoke show and in serious cases backfiring, yours doesn't seem to have that issue. Like NDT said, while running you should be able to turn the cap from retarded to advanced while running and hear the engine respond by running rough, then good, then rough (over retarded, timed, over advanced). What are the chances you have bad fuel or the ethanol in pump gas is messing with it? Never heard of that issue before but I've never asked soooo.... As far as degrees, I couldn't tell you, 8 sounds like a good starting point but I wouldn't think 12-14 to be too much. Something you may want to try if none of that fixes it is doing a compression test while the engine is hot, after it stalls out. Could be that after everything's hot and expanded compression is lost, doubtful, but possible.
Could be something silly like a gasket reversed in the carburetor, I bought a boat once with a rebuilt carb by the PO who put the intake to carb gasket in place of the throttle body gasket and vice versa . Sold the boat to me non running. I took a known good carb off the shelf, swapped it out and she ran like a top. Again, doubtful, but I like to leave nothing to chance. Hope you find the gremlin

 

[85J]

I adjusted the timing as was suggested by rotating it to each extreme. I set it to the smoothest running/highest vacuum at 12 degrees when cranking and 22 degrees when running.
I also adjusted the mixture screw to the smoothest running/highest vacuum. It didn't seem to make much of a difference unless it was run all of the way in.
The Jeep did run smoother, and with a higher vacuum, around 20 InHg. It did not stall when hot as long as I kept the RPM up, but it will not idle. When I try to idle it gets really rough and wants to die.
After it dies I cannot get it to restart on its own. It will sputter for about 1-2 revolutions and then nothing. If I give it starting fluid it will fire right up as long as I keep the RPM high.
Below are the results from a hot compression test:

 

[Mullaney]

I adjusted the timing as was suggested by rotating it to each extreme. I set it to the smoothest running/highest vacuum at 12 degrees when cranking and 22 degrees when running.
I also adjusted the mixture screw to the smoothest running/highest vacuum. It didn't seem to make much of a difference unless it was run all of the way in.
The Jeep did run smoother, and with a higher vacuum, around 20 InHg. It did not stall when hot as long as I kept the RPM up, but it will not idle. When I try to idle it gets really rough and wants to die.
After it dies I cannot get it to restart on its own. It will sputter for about 1-2 revolutions and then nothing. If I give it starting fluid it will fire right up as long as I keep the RPM high.
Below are the results from a hot compression test:
View attachment 932661

.
Compression looks good enough. What about the plugs? Have you checked the "gap" on them? #1 looks (might be just the pic) like it has been dropped on the electrode. They all look a little "worse for the wear" in my opinion.

 

[biscuitwhistler37]

I would definitely change those plugs out, re-gap at minimum. #1 looks closed fully and #2 looks wide open and a little burnt. Compression looks on the edge to me, 20% variation between low and high and 5-10% per cylinder tells me the valves may need adjustment, pattern is consistent low/high with firing order, valves probably aren't sealing properly/fully, if I took a guess I'd say valve timing on 1 and 4 is advanced (valves opening too soon). Numbers themselves look good, anything below 100 is cause for concern. 90% sure your issues lie within those two things.

 

[67Beast]

I see you said you replaced the points, rotor and cap, but did you replace the condenser? I just had a recent problem with mine after it bounced home on the trailer from the MVPA show in Oshkosh and it would not run correctly. It acted like it was a fuel problem, running rich and backfiring and would stall out. I tried several things and on a tip from another M38a1 owner, I replaced the condenser and it ran fine after that.

 

[NDT]

When I first got my M38A1 in 1980, it would stall like you are describing due to the float needle getting stuck and flooding the engine.

 

[85J]

Cleaning and gapping the spark plugs was one of the first things that I did. I just cleaned and checked them again and they are all at .030"
I also just did another cold compression test to compare the numbers to hot.


All of the spark plugs definitely look used but I don't see any problem with them. Please let me know if you guys disagree.

I did replace the condenser when I replaced all of the other distributor parts, I forgot to mention that.

I would definitely change those plugs out, re-gap at minimum. #1 looks closed fully and #2 looks wide open and a little burnt. Compression looks on the edge to me, 20% variation between low and high and 5-10% per cylinder tells me the valves may need adjustment, pattern is consistent low/high with firing order, valves probably aren't sealing properly/fully, if I took a guess I'd say valve timing on 1 and 4 is advanced (valves opening too soon). Numbers themselves look good, anything below 100 is cause for concern. 90% sure your issues lie within those two things.

I'm not sure what you mean by "valve timing." From what I understand the cam/valve timing is driven by the crank through the timing chain. Unless it has jumped a tooth or what set up wrong it should be correct? Are you referring to "valve timing" and valve lash/adjustment as the same thing?

When I first got my M38A1 in 1980, it would stall like you are describing due to the float needle getting stuck and flooding the engine.

I'll pop the top off of the carb and check. Hopefully the extra filter would have caught anything, but maybe something got stirred up from inside the carb. Hopefully the gasket survives.

 

[85J]

I also wanted to ask about the mechanical timing advance weights in the distributor. When using the timing light it seems like the timing advance weights are coming out and advancing the timing at anything above cranking rpm. I have 12 degrees when cranking and 22 at any rpm running, even around idle.
I'm used to seeing the mechanical advance, mostly on small block chevys, come on at around 2,000 RPM. I was surprised to see them come out right away.
Is this normal for these Jeeps or do I have worn out springs?

 

[biscuitwhistler37]

I'm not sure what you mean by "valve timing." From what I understand the cam/valve timing is driven by the crank through the timing chain. Unless it has jumped a tooth or what set up wrong it should be correct? Are you referring to "valve timing" and valve lash/adjustment as the same thing?

Apologies, yes I was referring to valve lash/adjustment as the same thing. 1 and 4 look like they're opening early or closing late, or vice versa, and it's resulting in a loss of compression on 2 cylinders, on the opposing cycle. Explains why the ignition timing isn't cooperating and why it won't start after it heats up. 1-3-4-2, low, high, low, high, consistently. If you find that fuel delivery isn't the issue, I'd definitely check valve lash.

 

[85J]

I adjusted the intake and exhaust valve lash. They were ALL over the place. I found intake lash ranging from 0.010-0.020" and exhaust lash ranging from 0.0090-0.018".
I set them to:
Intake: 0.018"
Exhaust: 0.016"

I also checked the carb bowl and float needle for debris and found nothing.

It was running a little better but still pops and the mixture screw did not seem to make much of a difference.
It will run but not idle and if I let it die it will not restart. If I give it a shot of ether it fires right up and runs.

I'm thinking it's a fuel delivery issue but I'm not sure why. I'm a little suspect of the fuel pump so I'm going to try gravity feeding the carb to see if that helps.