engine dies in 15 minutes

[happy1970GMC]

1970 GMC probably a '72 engine, 350, Q jet, auto tranny. Just replaced the mechanical fuel pump. It still dies at 13 to 15 minutes, and it will have to cool down for at least an hour, then do it again. Any help would be appreciated.

[68350]

What does it have to cool down for an hour? Will it not restart or?

[happy1970GMC]

It will turn over, but not fire. I've checked the gas cap, no vacuum in the tank. Just replaced the fuel pump, I can pull on the throttle and squirt fuel in the carb.

[68350]

Do you have an HEI distributor? Almost sounds like the control module or something is bad and when it gets heated up, it's causing the truck to die. Another thought I had was the motor is running too rich and maybe flooding itself out? Are your spark plugs wet?

[Ed F]

Sounds like it could be a plugged fuel filter to me

[Ken O.]

Just had the same thing on my 67 GMC. It had the points distributor on it. After it ran for a while, 10-15 min it would die, then not start again, Wait an hour and it would fire up and again after 10-15 min it would do the same thing again. I went through EVERYTHING and finally put a new HEI distributor in it and it runs perfect now, no issues in 2 months.

[davepl]

The HEI modules can get flaky when hot - if you have a spare distributor, that'd be my guess. My first guess was tank venting, but you said no vacuum, so HEI it is!

[happy1970GMC]

Thanks for the ideas, I'll get back to it next weekend.

[87Skier]

Had a 1990 Suburban do the same thing. Just needed new cap/rotor, plugs, and wires. Ran perfect after that. Check that distributor too.

[swamp rat]

Something else, there is a short rubber hose below the tank, if its getting old and rotted it can collapse and restrict fuel flow, that includes any rubber line between the tank and pump, make sure its actual fuel line that is reinforced and not non reinforced rubber hose...

Check the filter like previously mentioned, try and back flow it with some air and see if there are any fine white chards of material in it, if there is that is the pickup sock deteriorating, time to replace the pickup screen.

[Davidf]

+1 on ignition related components failing after heating up. Not too long ago, I purchased 64 Corvair and installed all new ignition parts. A mile or so down the road and it stop dead in its tracks. I decided to replace the points, condenser and ignition coil again...all was well the second time around. So, BOOB (Bad Out Of Box) parts are not uncommon.

[zeldman]

If it is the old points and condenser distributor, sounds like the coil is breaking down. To test it, remove it, then shake it, If it makes a sloshing noise replace it.

Could be the same for HEI.

[happy1970GMC]

Thanks for the ideas, I'll check them out.

[praisegeetarman]

Check that the fuel tank is venting. If you remove the gas cap and the problem goes away, then that's what it is.

[rripp]

I would bet its the coil.

[snipescastle2]

Also, if you replaced the hei module recently and didn't use the dielectric grease,the module will fry to a crisp.... just sayin'
Ben

[davepl]

Originally Posted by praisegeetarman

Check that the fuel tank is venting. If you remove the gas cap and the problem goes away, then that's what it is.

He said no vacuum in the tank in his initial description.

[kilrcady]

fuel filter

[71CHEVYSHORTBED402]

Tank vent > fuel filter > distributor.................More likely distributor than fuel filter, but a filter is cheap and easy. If all that fails, I'd replace all fuel lines, including the vent line. If that fails, couldn't tell ya.

Don't know if that could be a fuel pump. Seems it would work or it doesn't.

[snipescastle2]

Just something to check, but is there any fuel coming out the "Weep Hole" by chance? might want to make sure you have no fuel getting into your oil pan also....
Ben

[happy1970GMC]

Hello to anyone reading this, I put a new coil in today and doubled my run time. Now it will run for about 30 minutes. I bought a remote starter, but haven't figured how to hook it up, the directions are for a more modern vehicle. Can a part store test my module for me?

[EARNHARDT#3]

Originally Posted by happy1970GMC

Hello to anyone reading this, I put a new coil in today and doubled my run time. Now it will run for about 30 minutes. I bought a remote starter, but haven't figured how to hook it up, the directions are for a more modern vehicle. Can a part store test my module for me?

I don't think so. They sure can sell you a Chinese one that won't last either though. I have a stash of GM ones incase I ever need them. Go to the JY and grab a few if you can. Around here you won't really find anything that old but maybe you have a yard with older stuff nearby.

[Grumpy old man]

I still say it's a fuel issue , The dist ,coil,capacitor ,and anything else wouldn't continue to start multiple times and just run for 13-15 minutes ,It would have completely failed already .

Dirty fuel pick up in tank
Fuel line between tank and hardline under cab collapsing / cracked
Inline fuel filter
Bronze fuel filter in carb

it starts ,runs until crud in fuel line restricts flow .Won't restart ,wait an hour fuel flows back clearing line and restarts .Dies if 13-15 minutes . Why no pictures ? a good look at the condition of the rest of the engine/fuel lines and ignition could let someone give a further diagnosis .have you tried starting it once it dies using carb cleaner to see if it will fire even for a few seconds ?

[Shady Rascal]

You're either losing spark or you're losing fuel. Don't make it any more complex until you figure out which is the culprit.

When the thing dies, spray a spritz of carb spray or starter fluid down the carburetor. Does it try to start now ? If so, you have a fuel supply issue. If the spritz down the carb didnt cause it to try and start, pull a plug wire off and check for spark while cranking.

[bigjason]

When it dies look into the carb and see if the squirters are pumping fuel. Is the motor timed correctly? It could be getting hot due to poor timing and causing excessive heat that is vapor locking the fuel system. Are any fuel lines ran near the exhaust manifold?