Truck runs fine for about an hour or 90 mins then dies

[Juiceball]

Anyone had this issue? My '83 K20 has an older 454 in it with an HEI. The truck will run fine for about an hour or so then sputter and die. When it starts to sputter, there are surges of power like the spark is flipping on and off. When it dies, it will start again after a while but won't run again without sputtering and dying until it cools off for several hours. I changed the ignition module and switched coils (using an old coil from another Chevy that runs fine). Going to put a new cap, rotor, and coil on just to be sure, but I'm thinking it might be the condenser? Will heat affect that and would it even be the cause? Could it just be a bad wire somewhere that is getting hot? When it runs it runs fine, smooth, and strong so I don't think it's a fuel issue, but maybe?

Thanks, I'm stumped!

[Just1more]

There are a couple of things you need to check. When the truck dies, is it losing spark or fuel? To check if it's losing spark, pull a plug wire and put a good spark plug in it. Ground the base of the plug to the block and crank it over. If you see a bright blue spark jumping the gap on the plug, you have spark. Now, a quick check for fuel. When it dies, pull the breather off and pour a teaspoon or so of fuel down the throat of the carb, then crank it over. If it fires and tries to run, you probably have a fuel problem.

If we figure out which one you are losing, we can help you figure out why.

[Juiceball]

Haven't tried the spark plug trick but it will start again after it dies. I can compression start it a few times as I'm rolling to a stop. If it only sits a few hours it will start, idle, and take off, but only a few 100 yards before dying again. If it is a fuel issue, what would cause it to die after running perfectly for over an hour, at speed and under load? (New filter, new gas tank sender).

[Just1more]

You said you replaced the ignition module, did you replace it with a new one and did you coat the metal plate with the special heat transfer grease? I have seen those act similarly, they run fine until they heat up and then do all kinds of weird things.

[Juiceball]

Yep. New module and used the grease. The condenser lead was all twisted up and routed between the base plate of the distributor and the top of the engine so it was sitting right on top of the motor. I rerouted it so it went directly from the base plate to the cap. Was going to replace that (and condenser) next to make sure there isn't a broken or frayed wire that's getting to hot and choking out the signal from to many ohms due to heat.

[old Rusty C10]

years ago I had an f250 that had a similar issue with a condenser that was getting hot off the exhaust manifold and blowing a fusible link.. I would check the fuel pressure to rule it out but im betting that the condenser.. the other thing im suggesting you check is the whole distributor make sure there is no up and down play in the shaft
One other thought the coil you put in are you sure its good? Ive had several that came off the shelf in the suto parts store that were defective those were made by KEM since that incident years back I refuse to use anything other than AC Delco in the GMs

[mrolds88]

I kinda think its a fuel issue. 100 yards wouldn't heat anything up far enough to make it die (electrically), I wouldn't think. Also, to do the spark plug test, if you don't have a spare plug, just get a buddy to hold he end of the wire, but you have to do it early in the morning!! LOL Might not work any better, but will be more entertaining.

[hartbraker]

May be a stupid question, but could you guys elaborate on what condenser you're talking about? Pics would be nice... what does it do?

[SkinnyG]

If you are running out of fuel (no fuel squirting in the carb when you move the throttle by hand),

Try driving with the gas cap off.

If the tank isn't venting, at some point the fuel pump cannot overcome the vacuum created in the tank by the exiting fuel, and the engine starves. After a number of hours, the tank eventually equalizes pressure through what little remains of its vent, and you can drive for a time before it starves again. Removing the gas cap allows the tank to take on air as fuel is drawn out.

If nothing else, it's an easy test.

[Juiceball]

Originally Posted by hartbraker

May be a stupid question, but could you guys elaborate on what condenser you're talking about? Pics would be nice... what does it do?

Good point, here it is...you plug one end of the ignition control module into the condenser and pigtail plugs into the cap.

[Juiceball]

Originally Posted by SkinnyG

If you are running out of fuel (no fuel squirting in the carb when you move the throttle by hand),

Try driving with the gas cap off.

If the tank isn't venting, at some point the fuel pump cannot overcome the vacuum created in the tank by the exiting fuel, and the engine starves. After a number of hours, the tank eventually equalizes pressure through what little remains of its vent, and you can drive for a time before it starves again. Removing the gas cap allows the tank to take on air as fuel is drawn out.

If nothing else, it's an easy test.

Will try that but I just changed the sender unit and all flexible hoses. Vent cap seemed to be working. The other problem I haven't fixed is the starter. With the big block and headers the hot line to the solenoid or the solenoid itself gets to hot after running for a while so it has to cool down also. Going to install heat shield and heavier guage hot wire. Anyway, by the time the motor quits, so does the starter, so it's hard to turn it over right away after it dies. Best thing I can do is compression start it while still rolling which works a couple of times but it ultimately gets to the point where the motor just jake brakes the truck to a stop.

[Juiceball]

Thanks for all the ideas so far, gonna hit it again after coming to tomorrow::