Engine kills when hot: Round 2

[BarnabyHooge]

After replacing the intake gasket my old problem is still a problem. It's a '71 350.

The motor runs fine when it's cool. Idles pretty steady at 1000 in Park and 800 in Drive & Reverse. It's noticeably smoother now than it was before the new gasket. I can move it between the 3 with no problem.

After a while of city driving or just when the engine gets really warm (about 190 water temp), then motor will kill when it's at a stop. It doesn't bounce around first or make any sort of warning sign that it's about to go, the tac just drops.

Restarts with no problem, fires up as normal.

The only way it stays running is if I keep a slight touch on the accelerator at a stop with my other foot on the brake.

I've redone the plugs and fuel filters have all been replaced.

Any ideas? Any other tests that might help me figure this one out? I'm at wits end with this after my troublesome intake replacement.

[chipflyer]

Had the EXACT same problem with mine several years ago and believe it or not it was the module in the HEI. Bought a new module, put it in and the issue has not happened again. They don't always "completely" fail.

Jeff

[BarnabyHooge]

Hmmm.... I had the module tested and it came back ok. Of course, that was when it was cool. I guess my next question would be why it works with the throttle, and why it would be able to fire up again without issue.

[Shyguy]

When I worked at Auto Zone and O'Rielly's I always ran three test cycles on a module to make sure it was warmed up.

I have seen the first two cycles show the module was ok and it failed on the third cycle.

Modules are easy to replace and all auto parts places carries them.

I always carry a spare module just incase.

[mstrav1973]

dont overlook the possibility of vapor lock on the fuel line as well. what carb? good pump and filter?

Matt

[rennalds]

My sons truck had a similar problem. It all started after we went to a chrome air filter. I think the problem with this is that if your are still using the Q-Jet carb it needs the warm air from the exhaust manifold to close the choke once the engine gets hot. This is just a theory of mine. But when we changed out the carb the problem was solved. I think keeping your foot on the accelerator allows just enough air into the carb to keep it going.

[tim21391]

could it be this.. it might sound stupid but.. when the choke is on it will run higher rpms but once its warmed up and the choke is off with lower rpms maybe the idle isnt up enough to keep the truck going?

[cdowns]

do you have a lazymans rubber fuel line? they sometimes collapse internally or if resting on hot block or manifold cause a vapor lock type problem

if you have edelbrock carb and dont run a phenolic spacer the gas perculates in the carb

[BarnabyHooge]

It's a holley carb and performer rpm intake. The guy at Autozone tested it 10 times without a fail. Fuel line is solid and all three fuel filters were replaced.

A family member suggested it might be something going on with the vacuum advance.

[cdowns]

3fuel filters??? have you had this problem with just one?// i'd think the top priority is to get cleaned up reliable fuel supply system

[Shyguy]

Why 3 fuel filters, that can cause a problem with vapor lock if any of them are before the fuel pump and close to a heat source.

I know I have had that problem before.

[BarnabyHooge]

I've got 2 of the small hard filters in the carb and one of the canister types inbetween the pump and carb.

It's a manual choke, which I've had open at start without issue.

[BarnabyHooge]

Any other thoughts? It doesn't seem like a spark issue since it fires up and runs fine when the throttle is engaged even just a small amount. I'll certainly address the module but I'd like to rule out a few other things before I dole out the cash.

Is there something wrong with having those 3 fuel filters?

Thanks!

[storm9c1]

One way to eliminate fuel problems is to test the fuel pressure. Buy a diagnostic fuel pressure gauge and temporarily tee it into the fuel line right at the carb inlet. Run a rubber hose under the hood and through the window and keep an eye on it during a test drive. Of course use clamps on the hose and be smart about the routing. It only has to last a drive or two.

When I did this, I noticed my fuel pressure would drop to zero and a moment later the engine would die. Turned out that the PO put a filter before the pump and on hot days, the pump couldn't get enough volume to keep up with the carb (and easily vapor locked). I had to move the filter to the pressure side. And running multiple filters doesn't sound beneficial either.

If that checks out OK, then it could be ignition related.

[BarnabyHooge]

I'll give that a try, definetly worth a shot.

[coloradosean2009]

heat from intake - get a spacer.

[BarnabyHooge]

I think I got this licked and it looks like Chipflyer had it right.

Even after testing the coil myself and having the module tested at Autozone, it looks like a full on dist. replacement fixed it. A family member told me it was probably the coil, and after seeing a bunch of good comments on the Skip White HEI I decided to just get the whole kit and kaboodle rather than trying a new module for $35, and then maybe having to go with a new coil as well.

I drove it Sunday in some serious traffic on the freeway with no killing or stuttering what so ever. You've never seen a bigger smile on a guy stuck in traffic.

Thanks everyone!

[mclairmo]

Congrats. Electrical components hate heat and when you have heat only related driveability issues, they often can be traced to weak electrical components that fail when hot.

[D.PASSMORE]

Basic theroy of a gas powered engine: It takes fuel and fire to run it. If it dosen't run, you have to eliminate one. Intermitted problems are the hardest to figure out. Glad you have a solution! DP