1949 Plymouth Special Deluxe Won't start when engine hot

[Tim Larson]

My '49 Plymouth starts great from a cold engine, but after driving it around for approx. 10 miles it started to backfire and then the engine slowly lost power and then died for me. After it cooled for about an hour it started fine.

 

Since I got the car I've changed oil/filter and changed spark plugs. There is fresh gas in the tank and before starting the engine I can see fuel spray into the carb. - this is from a cold engine.

 

There are no heat shields around the carb or fuel pump.

 

I'm taking it to an experience mechanic next week, but has anyone ever experienced this before?

Edited July 11, 2019 by tjlarson88

[plymouthcranbrook]

Sounds fuel related.  Have you tried spraying a little gas into the carb when it stalls and see if it restarts?  If it does perhaps the fuel pump is failing. Does it run hot?  And does the Heat riser work correctly?

Edited July 11, 2019 by plymouthcranbrook

[Tim Larson]

Yes, this did nothing... we checked an there is power at the coil. There is power to the plugs when cranking.

 

There seems to be dampness on the floor under the fuel pump when it’s sitting in the garage. Is that possible?

[plymouthcranbrook]

Fuel?  Could be a small line leak?  That would suck air instead of fuel from the tank and cause a stall. But that would seem to be something that would happen all the time.

Edited July 11, 2019 by plymouthcranbrook

[keithb7]

Compression test. That should let you know where to look for clues going forward. 

[plymouthcranbrook]

Good idea keithb7. Should read at least be 100 psi or so and all cylinders  should be relatively even.

[Tim Larson]

Would a compression issue show up more when the engine is at operating temps? Or would it always cause problems?

[plymouthcranbrook]

If possible do at operating temp. Better more accurate readings.  Be sure to remove all 6 plugs before starting test.  And allow a couple three pulses on the gauge to get the best reading. After you do the original test if there is a large variation (20% or so) You can do a wet test by putting a little oil in each cylinder to see if the test improves.  If it does most likely a ring problem

Edited July 11, 2019 by plymouthcranbrook

[Tim Larson]

10 minutes ago, plymouthcranbrook said:

Sounds fuel related.  Have you tried spraying a little gas into the carb when it stalls and see if it restarts?  If it does perhaps the fuel pump is failing. Does it run hot?  And does the Heat riser work correctly?

 

The temp gauge showed a little above 160, but not too much when I was going on the highway. I’m not sure about the  me heat riser...

[plymouthcranbrook]

That is not hot.  You can check the heat riser by moving it  by hand on a cool engine and see if it is free.  It directs heat from the exhaust to the area under the carb for better fuel dispersion when cold and if too warm might cause lean running on a hot day.  Never had an issue with this myself but something to check.

[keithb7]

Tell us a little more. 

 

How long have you owned the car?  Did it drive fine, hot or cold, for some time? Then recently start acting up?

 

Improperly set valve lash may allow the engine to start when cold and run quiet. Upon heating up the valves, they expand. If clearance too tight, they’ll stay open enough that the engine may miss, backfire and will not start again until cooled off. 

 

Just an idea. Not saying that’s the answer. A cold & hot compression test may reveal a few things.  

[Plymouthy Adams]

check your coil, though it runs good cold, it will overheat if on the way out....it will die and later restart when cold.  You can still see a light amount of spark but it is not strong enough to fire a lean engine...

[Tim Larson]

2 minutes ago, keithb7 said:

Tell us a little more. 

 

How long have you owned the car?  Did it drive fine, hot or cold, for some time? Then recently start acting up?

 

Improperly set valve lash may allow the engine to start when cold and run quiet. Upon heating up the valves, they expand. If clearance too tight, they’ll stay open enough that the engine may miss, backfire and will not start again until cooled off. 

 

Just an idea. Not saying that’s the answer. A cold & hot compression test may reveal a few things.  

 

I have owned the car the car for almost two weeks. It had this issue with not starting when warm/hot after I got it home. It did not act up when test driving...

[soth122003]

I'm with Plymouthy. Sounds like the coil. I've got a couple of spares just in case and they are not that expensive. Any auto parts store has them and I believe you can get them from Amazon as well. Also changing the coil takes about 5 minutes and anyone can do it.

 

Joe Lee

Edited July 11, 2019 by soth122003

[Bobs]

Check fuel line to fuel pump, mine had a crack in it. Would start cold, but not hot, I would have to have it sit for awhile to restart . Change the hose, fix problem

[plymouthcranbrook]

Coil failure was a problem on some Fords back in then 80's and 90's My neighbor ran his own repair business in his garage and I know he changed out several of the them That did the same thing you describe. I had forgotten  about it until the other posters mentioned it.

[Greg51T&CWagon]

In addition to the coil. I'd check the distributor cap and wires. look for corrosion or cracks. The wire contacts where they plug into the cap should be clean without oxidation etc. I recently had this problem with another car. I installed new wires and a cap and problem solved.

[Tim Larson]

I think the wires are original to the car and some don’t fit that tight on the end of the plugs. Definitely something to check!

[kencombs]

On 7/10/2019 at 9:26 PM, tjlarson88 said:

My '49 Plymouth starts great from a cold engine, but after driving it around for approx. 10 miles it started to backfire and then the engine slowly lost power and then died for me. After it cooled for about an hour it started fine.

Since I got the car I've changed oil/filter and changed spark plugs. There is fresh gas in the tank and before starting the engine I can see fuel spray into the carb. - this is from a cold engine.

There are no heat shields around the carb or fuel pump.

I'm taking it to an experience mechanic next week, but has anyone ever experienced this before?

I would suspect either the coil or condenser.  Those are the items most likely to be affected by heat.  the backfire sure speaks to ignition rather than fuel, at least IME.  The distributor cap could be at fault also, but those are not normally heat sensitive.

[jhm1mc13]

My money is on the coil.

[greg g]

Wait till after dark, open the hood, start the car and look for Sparks where there shouldn't be any like between spark plugs and wires, from the wire down the side of the  spark plug, from the coil wire to the mounting bracket.  Electricity like water will take the route of least resistance.  Tis might show you where some of you problems are.

[packardmanken]

I have been struggling with the same thing for 11 months and may have got to the bottom of it. The two jumper wires in the distributor are woven cloth covered. they must have been the originals. After looking very closely, i found a bare spot where one had grounded on the inside side of the distributor. The other one flexes slightly when accelerating and too had lost its insulation at the bend. I had tried EVERYTHING. New coil,  metal threaded spark plug wires. New points, condenser, plugs, rotor and cap. The coil i bought was a flamethrower from pertronix for 6v and had to have special ceramic thingiy in the line to the coil. all new wiring everywhere into the switch. Then I saw these two wires in the distributor. Taped them up and the car did great!!! I have since replaced the whole distributor with a spare i had that had been rebuilt 50 years ago.  I tuned it with a vacuum gauge and it starts and runs flawlessly now. Timing light was useless compared the the vacuum gauge. 

The whole point of my story is it probably something really really simple. just keep working thru the pieces one by one. keep a record of what you have replaced. I wrote down everything that was involved and checked it off as i went thru it. I have pulled out almost every hair (and there isn't much) on my head. If it were not for the help from this group, i would not have got thru this. You will get it! Don't give up

[Plymouthy Adams]

while the event that you describes is truly a weak point and an area one should visit for reliability. the fact  it starts, runs without grounding out and only when the heat of the coil weakens the field to where it can no longer sustain a spark does the engine cough and die and when later it COOLS, the engine will restart and repeat said cycle of event...

Edited July 13, 2019 by Plymouthy Adams

[Tim Larson]

1 hour ago, Plymouthy Adams said:

while the event that you describes is truly a weak point and an area one should visit for reliability. the fact  it starts, runs without grounding out and only when the heat of the coil weakens the field to where it can no longer sustain a spark does the engine cough and die and when later it COOLS, the engine will restart and repeat said cycle of event...

Your description of the situation leads me to believe you think it could be the coil, as well.

[Tim Larson]

1 hour ago, packardmanken said:

I have been struggling with the same thing for 11 months and may have got to the bottom of it. The two jumper wires in the distributor are woven cloth covered. they must have been the originals. After looking very closely, i found a bare spot where one had grounded on the inside side of the distributor. The other one flexes slightly when accelerating and too had lost its insulation at the bend. I had tried EVERYTHING. New coil,  metal threaded spark plug wires. New points, condenser, plugs, rotor and cap. The coil i bought was a flamethrower from pertronix for 6v and had to have special ceramic thingiy in the line to the coil. all new wiring everywhere into the switch. Then I saw these two wires in the distributor. Taped them up and the car did great!!! I have since replaced the whole distributor with a spare i had that had been rebuilt 50 years ago.  I tuned it with a vacuum gauge and it starts and runs flawlessly now. Timing light was useless compared the the vacuum gauge. 

The whole point of my story is it probably something really really simple. just keep working thru the pieces one by one. keep a record of what you have replaced. I wrote down everything that was involved and checked it off as i went thru it. I have pulled out almost every hair (and there isn't much) on my head. If it were not for the help from this group, i would not have got thru this. You will get it! Don't give up

I believe this same situation might have been an issue on my '52 Merc. I know my mechanic replaced a wire on the distributor when I was having trouble in the past.

 

I agree that it probably is something simple - the whole operation of motors in this era are really not complicated - everything just needs to be working together properly.

 

Thanks!