When hot it sputters & dies, wait, starts and runs great, repeat

[John94]

Hello, everyone. We have a 1994 GT 5.0 conv with only 83k orig miles, but it has a recurring issue that we, and several mechanics, have not been able to figure out.

The engine runs great, until it gets hot – then it starts to “sputter” and the engine dies abruptly. After it dies, the engine won’t restart. You have to let it rest 20-30 minutes or so. Then it will start right up, runs great like nothing ever happened for a few miles, and then the process starts again – sputters & dies, wait, starts and runs great, repeat.

We have thought it might be an ignition, fuel, or mass air flow sensor issue, and the following repairs have been performed, but still haven’t solved the problem:

Prior owner
Replaced O2 sensors
Replaced fuel filter
Replaced radiator, water pump
Replaced mass air flow sensor
Repaired air intake leak

Current owner
Cleaned mass air flow sensor multiple times
Replaced mass air flow sensor multiple times, with both aftermarket and Motorcraft part
Replaced ignition module (it is mounted in the heat sink on the fender, not on the distributor)
Replaced distributor
Replaced fuel filter

At last service at the shop, DLC scan shows no codes. A fuel pressure gauge was installed, car was driven for a few miles and fuel PSI stayed at spec.

Anyone have suggestions on what we should try next?

WOW! You are talking about my 94 GT except my engine has a complete overhaul with gt40p heads because one of my E7 had internal coolant leak, I've replaced everything I and others can think of but mine puts out lite black smoke till warmed up blackening the plugs before shutting down. We may be looking for the same solution.

 

[07GtS197]

WOW! You are talking about my 94 GT except my engine has a complete overhaul with gt40p heads because one of my E7 had internal coolant leak, I've replaced everything I and others can think of but mine puts out lite black smoke till warmed up blackening the plugs before shutting down. We may be looking for the same solution.

Your issue sounds fuel related. Have you pulled codes? If the plugs are fouling that quickly something is causing the ecu to dump fuel.

 

[94SVTCobra]

I'm following this with interest. I also have a '94 Cobra 5.0 5 speed with about 75,000 miles. I bought it about 20 trouble-free years ago. Mine has sounded/felt like it wanted to quit....cough...sputter - it felt like 3-4 spark plug wires came off as I was driving along under normal conditions - but has never actually quit. No dash lights have come on at all. After it sits for a while, it runs fine again for weeks. this has happened 2-3 times in the last 6 months. I have a friend who has a DBS 1 (or whatever that diagnostic tool is called). We're going to hook that up when he gets back in town. Hopefully it will tell us something. The uncertainty gets old quick!

I would replace the stator/hall effect sensor just as preventive maintenance. Regards

 

[Admiral_peck7]

Hello, everyone. We have a 1994 GT 5.0 conv with only 83k orig miles, but it has a recurring issue that we, and several mechanics, have not been able to figure out.

The engine runs great, until it gets hot – then it starts to “sputter” and the engine dies abruptly. After it dies, the engine won’t restart. You have to let it rest 20-30 minutes or so. Then it will start right up, runs great like nothing ever happened for a few miles, and then the process starts again – sputters & dies, wait, starts and runs great, repeat.

We have thought it might be an ignition, fuel, or mass air flow sensor issue, and the following repairs have been performed, but still haven’t solved the problem:

Prior owner
Replaced O2 sensors
Replaced fuel filter
Replaced radiator, water pump
Replaced mass air flow sensor
Repaired air intake leak

Current owner
Cleaned mass air flow sensor multiple times
Replaced mass air flow sensor multiple times, with both aftermarket and Motorcraft part
Replaced ignition module (it is mounted in the heat sink on the fender, not on the distributor)
Replaced distributor
Replaced fuel filter

At last service at the shop, DLC scan shows no codes. A fuel pressure gauge was installed, car was driven for a few miles and fuel PSI stayed at spec.

Anyone have suggestions on what we should try next?

If you can get access to an external wideband like dyno guys use, maybe see if you can run it up to temp and see if it goes rich or lean and run from there, if going rich maybe suspect issues with the return or the regulator, if you're going lean I'd almost wonder if it's a vapor locking issue, though that's rare on EFI.

 

[Monday]

Exact same problem year and a half ago. Two things happened at pretty much same time on mine. One was my MAF. Two was my fuel sending and gauge. Replaced them both and 5x5 ever since.

Running out of gas and when I unplugged the MAF, it would start immediately - when it was nice and hot.

 

[94SVTCobra]

I still say Stator/Hall effect sensor. It's the one buried deep in the distributor. A faulty unit often malfunctions only after it is heated up, like it did on mine.

ColoMustang21: Have you figured it out yet, or tried anything further that didn't work?