Persistent stalling after warm-up

[Mark Kevin Weaver]

My 76 NYB 440, runs fine until it is really warmed up.
It developed this after a highway run.
Now, every time I drive her, she runs fine until well warmed up then the engine begins to stumble and miss finally stalling completely.
Once she stalls there is no restarting.
The starter just turns the motor over without any sign of ignition.
After about 20 minutes of waiting, I can re-start and usually get back home.
Occasionally when stepping on the gas she will back-fire through the carburetor.
I've checked and changed the fuel filter and replaced the ignition module.
Any ideas where I can look next?

 

[413]

Is the choke open fully when the engine is warm?

Does it have lean burn or electronic ignition?

 

[Big_John]

My 76 NYB 440, runs fine until it is really warmed up.
It developed this after a highway run.
Now, every time I drive her, she runs fine until well warmed up then the engine begins to stumble and miss finally stalling completely.
Once she stalls there is no restarting.
The starter just turns the motor over without any sign of ignition.
After about 20 minutes of waiting, I can re-start and usually get back home.
Occasionally when stepping on the gas she will back-fire through the carburetor.
I've checked and changed the fuel filter and replaced the ignition module.
Any ideas where I can look next?

I have seen the distributor pickup fail just like this. Another possibility is the coil.

@halifaxhops sells a copy of a really good guide to diagnosing the electronic ignition. SOLD - electronic ign Trouble shooting book

 

[Fury1969WI]

to me that sounds like a failing ignition module, but you replaced that. Was it with an "known" good one? Good luck!

 

[Mark Kevin Weaver]

Is the choke open fully when the engine is warm?

Does it have lean burn or electronic ignition?

No lean burn and the choke does open correctly.

 

[halifaxhops]

Possible pick up coil also!

 

[3C's & a D?]

I vote for coil! Take the wire to the distributor off, see any oil? If so, replace.

 

[CBODY67]

How many miles on the motor? Just thinking about a fuel pump push rod being worn.

When it dies when warm, is there accel pump shot in the TQuad?

IF the issue started just as the carb got off of the fast idle cam, to the "hot base idle" situation, THEN I would say it was a carb issue for sure. BTDT! But your description does sound like ignition to me.

I do know that the ignition coil is in most trouble tree diag lists, but I have never seen or had one fail, personally. I have even changed coils with a new one (in this case, an ACDelco brand coil in the later 1980s (the new replacement was completely unmarked/unidentified by anything but a small, oblong gold "Japan" tag on the bottom!). The OEM stock coil ran just as well, so I put it back in).

Which now points to the ign module and/or the pickup coil in the distributor. The pickup coil, like the points it replaces, must have the correct gap between it and the trigger/reluctor that triggers it (using a brass feeler gauge to measure the gap).

In our current world of electronic parts, "new" is not generic and does not mean "better" than what came on the car OEM. Brand matters, usually, too!

Just some thoughts and observations,
CBODY67

 

[Kaim]

I had similar problems. Loose distributor shaft and bad pickup. That's the reason.

 

[Mark Kevin Weaver]

Well, I took her out for a trial run after replacing the coil and ignition module (again) and she started right up and idled for a good while, so I figured a short ride was OK.
Bad decision.
Started off good, stepped into the gas at a red light and suddenly several backfires from the exhaust and then died.
No restart or even a hint at trying.
Flat bedded home.
Could I have jumped timing?

 

[3175375]

Well, I took her out for a trial run after replacing the coil and ignition module (again) and she started right up and idled for a good while, so I figured a short ride was OK.
Bad decision.
Started off good, stepped into the gas at a red light and suddenly several backfires from the exhaust and then died.
No restart or even a hint at trying.
Flat bedded home.
Could I have jumped timing?

Maybe the timing chain has jumped a tooth?

 

[CBODY67]

IF the timing sprocket is still OEM, replace it. Put a timing set in with metal sprockets. Even if it is an OEM replacement and not a double-roller timing chain set.

The car might be low miles, but the plastic on the sprocket (if it is OEM) is still as old as the car. Best to just replace it for "insurance reasons" against any future failures.

You can also plan on removing the oil pan to clean it of any "fallen plastic items" from the cam sprocket, too.

As a test . . . you can put the transmission in gear and slowly load the engine against a firmly=applied foot brake. Raises rpms and also load on the motor at the same time. You can also pat the accel pedal to simulate acceleration from a stop, too.

CBODY67

 

[law]

Hello I just registered to let you know that I had the same problem last summer on my 1977 New Yorker. My issue was with the fuel getting too hot causing vapor lock. It would start running rough after driving for a few minutes and would not start up again until the engine cooled down. it would do this every time. I fixed it by using a three way fuel filter and plumbing a return line to the fuel tank, ensuring that fresh cool fuel is drawn constantly from the tank instead of allowing it to sit in the fuel line in the hot engine bay. I've also ordered a new fuel line going to the carb and made sure that it wasn't touching any part of the engine. I also put an insulating sleeve on it just for good measure. There are lots of resources explaining the concept of vapor lock in classic cars which helped me put together my solution. This is my case and could be what is going on with your car, or it could be something the others have mentioned here. I'm just giving my input and experience, good luck.

 

[3C's & a D?]

In your first post you mention the starter will turn over, but seemed to not have spark. This last post you say "no restart or even a hint at trying". It's possible you skipped a tooth or two when you gunned it. Try slowly turning the crank bolt with a breaker bar to determine.

There's still the original problem though, old fuel lines/fuel? Carburetor not tuned properly? It does sound ignition related, however as the guy above pointed out, it also sounds like vapour lock/fuel issue? These ones can be tricky. Pictures sometimes help.

 

[Rubatoguy]

Hello I just registered to let you know that I had the same problem last summer on my 1977 New Yorker. My issue was with the fuel getting too hot causing vapor lock. It would start running rough after driving for a few minutes and would not start up again until the engine cooled down. it would do this every time. I fixed it by using a three way fuel filter and plumbing a return line to the fuel tank, ensuring that fresh cool fuel is drawn constantly from the tank instead of allowing it to sit in the fuel line in the hot engine bay. I've also ordered a new fuel line going to the carb and made sure that it wasn't touching any part of the engine. I also put an insulating sleeve on it just for good measure. There are lots of resources explaining the concept of vapor lock in classic cars which helped me put together my solution. This is my case and could be what is going on with your car, or it could be something the others have mentioned here. I'm just giving my input and experience, good luck.

Also, if you use fuel with Ethanol the blend is more likely to vaporize than non-ethanol gas.

 

[Jakter]

If this is a new problem that never happened before it's not because of ethanol blend fuel.

 

[Big_John]

Well, I took her out for a trial run after replacing the coil and ignition module (again) and she started right up and idled for a good while, so I figured a short ride was OK.
Bad decision.
Started off good, stepped into the gas at a red light and suddenly several backfires from the exhaust and then died.
No restart or even a hint at trying.
Flat bedded home.
Could I have jumped timing?

IMHO. The part that was causing your initial problem has completely failed. That's not a bad thing.... Now you can find it.

What often happens is you'll have an intermittent failure, and in this case, heat was bringing on the failure and then it finally just fails. Things like timing chains don't do that.

If you want to throw parts at it, the one I would suggest again is the distributor pickup. $30 part. If nothing else, at least check the gap. I suggested buying the manual on diagnosing the ignition and I'll suggest that again. There's probably some YouTube videos on diagnosing ignition problems too. All you need is a simple multimeter, even the cheap Harbor Fright version will do.

It's possible it's a fuel problem, but I kind of doubt that too.... It would still be intermittent if it was.

 

[WissaMan]

How about the ballast resistor? I think heat affects them once they start going bad. You can test the voltage at the coil, but it's cheap enough to just throw a new one on. Though in my personal experience, a bad one wouldn't cause miss and stall but not backfiring. If it is a fuel problem, that could be troubleshot by hitting the carb with some starter fluid. (But be careful if you're getting backfires)

 

[Mark Kevin Weaver]

Today I replaced the ballast resistor, coil and distributer pickup (gaped per manual) now it doesn't run at all on her own. If I squirt it with starter fluid, she'll fire then die. The wife is SO done with this car. Sad because we both loved cruising with the windows down.

 

[Mr C]

Be methodical and calm you'll get it back running...do not despair. We've all been there and I know it can be frustrating, but these are way easier to fix than the new computer EFI stuff.

You'll get it, I'm sure.