M37 idles fine but just dies unexpectedly when being driven.

[m3751]

M37 idles fine but just dies unexpectedly when being driven.

I keep running into a problem with my M37 where I’ll be out driving it around town and it just starts chocking and dies.

Here is what works well:

• I can start the vehicle with no major issues. (starts within 5-6 seconds usually)
• Once started, it idles without any issue.
• With the vehicle in neutral I can rev the engine without issue.

The issue:

• After driving for about 15 minutes the vehicle starts chocking violently like it’s running out of fuel. I know this is not the case since I had just filled the tank less than 10 miles previously. I also installed a clear fuel filter just prior to the carburetor and can definitely see fuel going through. This situation has now happened to me 6 times. I think the local tow truck guys are ready to drop me from the plan…
• To try to solve this I did the following items to no avail.
  • Installed NOS fuel pump
  • Installed NOS carburetor
  • Installed new air cleaner
  • Installed new fuel filter in tank and installed extra one in front of carburetor
  • Installed new coil
  • Installed new distributor
  • Installed new spark plugs
  • Installed electronic ignition
  • Did an oil change
  • Installed new DC power line to the distributor
  • Drained the fuel tank and carb and put in all new fuel

I’m really at a loss as to what this could be, the only thing I have not changed are the spark plug cables and that just doesn’t sound like a symptom a bad cable would cause.

Anyone have an idea what else I should look at?

 

[glcaines]

I once had a similar issue with a non-MV and didn't know for certain whether it was fuel or spark related. I took a timing light and put it inside the vehicle where I could see it. I selectively put the pickup on the coil wire and then each spark plug wire and drove it each time. I proved that there was not a spark-related issue and could then concentrate on the fuel. Turned out it was a bad fuel pump relay.

You might also want to check the coil. I've had coils go bad as they get warm.

 

[m3751]

Hi Gary,

Thanks for the tip. Now that you mention it - I think this issue of unexpectedly dying when being driven happened after I replaced the coil about 6 months ago. Prior to that I was having trouble getting the vehicle to start, could very well be a thermally related issue.

Thanks,
Ted

 

[glcaines]

Hi Gary,

Thanks for the tip. Now that you mention it - I think this issue of unexpectedly dying when being driven happened after I replaced the coil about 6 months ago. Prior to that I was having trouble getting the vehicle to start, could very well be a thermally related issue.

Thanks,
Ted

Now that I think about it, it could also be the condenser.

 

[m3751]

With the electronic ignition (MV-161 from Pertronix) installed the condenser is removed. I do remember when I put the new electronic ignition in that I was a little concerned about the quality of the ground connection that the adapter plate had. Maybe that's making an intermittent connection when it gets hot.

Certainly some type of intermittent electrical connection could explain this type of problem.

 

[ranger.41]

Is there a military Distributor installed on the engine. If so are the cooling tubes in place,also called vent lines, and are they clear? If you feel that it might be the an intermitten ground check all grounds and use ground washers. I'm intrested in how the Petronics ignition is working for you. Good luck.
ranger.41

 

[ranger.41]

Do you have the heat shield that goes above the fuel pump installed? How far away do you have the fuel line from the exhaust manifold? Also check your fuel cap to see that it is set for vented. There is a tab that is turned to vent or unvented on the back of the fuel cap.
ranger.41

 

[captain-crank]

Set up a gravity fuel feed.

This will help isolate the problem for you.

Remember to disconnect/shut off fuel line into pump so fuel doesn't shoot everywhere.

Seems like you've done everything except the fuel lines.

They may have a blockage or restriction.

 

[MDSA]

Because of the waterproof ignition system on the M37, the vent lines previously mentioned by ranger are crucial. Your coil is completely enclosed and will get hot. I got my M37 in September, had similar problems and finally found that the previous owner had misdirected one vent line and plugged its hole to the carb throat.

There should be 2 small metal lines forming a loop for air to cool the distributor. They go from the bottom of the distributor, across the head to the carb throat. Inside the throat they should have small tubes facing opposite direections, one to receive fresh air, one to expell warm air. This is important. Make sure the lines are clear of junk.

 

[zak]

Some of the foreign made coils are junk.

 

[1958 M274]

I've had similar problems before on other vehicles. Two more things you may want to check are the fuel tank vent (might be stopped up making it difficult for the pump to draw fuel as the level goes down) or more likely your rubber fuel hoses. Sometimes they'll swell up inside and restrict the fuel flow while still appearing to be in good condition on the outside. Good luck!
Joe

 

[vtdeucedriver]

All good solutions to check. My 1st thought before reading others posts that with all the stuff you have changed, it sounds like a fuel vent issue. Go drive around with the cap off and see if it stays running.

 

[m3751]

Ranger,

The fuel pump is NSO, not an electric aftermarket type. I'll have to double check on the heat shield - I'm 99% sure it is there. Are you thinking vapor lock?

Regarding the MV-161 - it really made a big difference, I used to have a big issue with hesitation when I'd step on the gas, but this completely eliminated that and now the acceleration of the engine is super smooth.

 

[m3751]

The vent idea is interesting. I recently changed the flexible tube that goes between the filler and the tank to plug a leak; I think the issue started after I changed that. I'll have to take a look at the vent line and make sure it's not plugged.

Great suggestion - Thanks,

 

[ranger.41]

M3751,
I was thinking vapor lock. I routed my fuel line very close to the fenderwell away from the the exhaust manifold.
ranger.41