runs good, then bad, then shuts down

[screeminDemon]

Could use some suggestions. I appreciate the help. My 360 recently had electrical problems. It would suddenly randomly, immediately shut down even tho it was running great... slow speed and/or freeway speed. Then got to the point it wouldn't start. I ended up swapping in a new ECU box and it was running good again... for about 15 minutes and then started running rough to the point I had to give more gas at idle to prevent it from stalling. Then it stalled. Would not start again until cooled down. So now it's in that same pattern. After getting to full operating temp, 180, it starts to get rough and need to give it more pedal to keep it going until ultimately it shuts off. I feel like this is a fuel problem. I swapped in a new fuel filter but that didn't solve it.

360 has a mild cam, edelbrock alum intake, 800cfm thermoquad carb, stock fuel pump, stock 360 heads, stock pistons with low compression 8:1

 

[Bewy]

Congrats on using the TQ. Smart guy!

It sounds like flooding. If the carb has a lot miles on it, n/seats could be worn. They can also cause a higher float level. Anyway, they need to be checked. Usually you can remove the TQ airhorn without breaking the gasket. Another possibility is a 'heavy' float [ has absorbed petrol ]. A good nitrophyl float will weigh between 7.5 & 8 gms.

 

[halifaxhops]

If it is dropping spark for sure then the pick up is on its way out.

 

[G70464]

Could use some suggestions. I appreciate the help. My 360 recently had electrical problems. It would suddenly randomly, immediately shut down even tho it was running great... slow speed and/or freeway speed. Then got to the point it wouldn't start. I ended up swapping in a new ECU box and it was running good again... for about 15 minutes and then started running rough to the point I had to give more gas at idle to prevent it from stalling. Then it stalled. Would not start again until cooled down. So now it's in that same pattern. After getting to full operating temp, 180, it starts to get rough and need to give it more pedal to keep it going until ultimately it shuts off. I feel like this is a fuel problem. I swapped in a new fuel filter but that didn't solve it.

360 has a mild cam, edelbrock alum intake, 800cfm thermoquad carb, stock fuel pump, stock 360 heads, stock pistons with low compression 8:1

Check your bulkhead connector. Mine randomly shut off because the bulkhead was getting hot.
Other places is pickup in distributor
Coil
Check float levels
Vacuum leaks
Fuel pump

 

[Super-Cuda]

I'm with HalifaxShops on this one.

Easy way to check.

Buy one of these. really cheap!

Use it when the car is not starting.

You will need a helper to turn the key while you observe the tester.

Insert it between the coil and the coilwire. then check for spark in the tester by trying to start the engine . If ok, then insert between the sparkplug and ignition wire boot. Try starting the engine. If no spark in the tester , you have an ignition problem , not a fuel delivery problem.

 

[ir3333]

that's like going to a doctor and saying i have a pain...and you have been given some good guesses.
i had the exact same problem twice. One time it was the ECU, maybe your replacement is bad. The other
time it was caused by a fuel tank vent being plugged.You will hear the pressure release when you take the
gas cap off....do this as soon as it stalls to check before the pressure equalizes.

 

[dano]

Folks have made some good things to check out. I'll add verify a good ground at the ECU chassis.

 

[Dartsun]

I’d check the bulkhead connections and the coil. I’ve had issues with hot coil killing engine then runs fine after sitting for awhile.

 

[screeminDemon]

Thanks for all of the suggestions! I will dig into it this weekend and see what I come up with.

PS - Love that spark tester tool Super-Cuda! I need to get me one of those..

 

[Super-Cuda]

Thanks for all of the suggestions! I will dig into it this weekend and see what I come up with.

PS - Love that spark tester tool Super-Cuda! I need to get me one of those..

That little sucker saved me a lot of work on my 2001 Dodge Ram, 5.2 Magnum.

Engine turning over but no start. Everything pointed to crank sensor which is , as anyone whoever change one knows, is a real ***** of a job to do.

Installed it on the coil...good, installed in on an ignition wire...good. Depressed the center of the shrader valve on the EFI rails...no pressure. Problem was in tank fuel pump. Replaced, all good!!

 

[Divenut]

I'm with HalifaxShops on this one.

Easy way to check.

Buy one of these. really cheap!

Use it when the car is not starting.

You will need a helper to turn the key while you observe the tester.

Insert it between the coil and the coilwire. then check for spark in the tester by trying to start the engine . If ok, then insert between the sparkplug and ignition wire boot. Try starting the engine. If no spark in the tester , you have an ignition problem , not a fuel delivery problem.


View attachment 1716099840

This thing has helped me trouble shoot everything from mowers to my Duster. One of them tools I don't use often, but glad to have when I need it.