1992 Cadillac Limo by Superior 5.7L TBI

I purchased this car 1.5 years ago and it has run like a top-only 50,xxx miles. The older folks we run with here in Florida just love it. Easy to get in and out of and it is very stately being the presidential style.

It recently began to hesitate, stumble, no throttle response and then die after running the car for 20 minutes. It seems this is occurring when the car gets up to operating temp. If I wait 20 minutes it will again run great until it gets warmed up again and then the same thing occurs. On a couple of occasions I thought I smelled unburnt fuel when this happened. Doesn't smoke or backfire. Doesn't seem to be overheating although not equipped with a temp guage it has an idiot light that does not come on. It doesn't smoke or backfire. The onboard diagnostics computer (OBD I or ALDL) is not throwing any codes.

After doing a lot of research I thought it was a fuel mixture problem so changed out the oxygen sensor, temp sensor that feeds the computer and new plugs and wires without any improvement. I hate throwing parts at it without knowing what the problem is. I ordered a bunch of regular maintenance items (EGR valve, fuel filter, rotor distributor, thermostat etc,etc) thinking it's 29 years old and I don't have a lot of history on it and it will need replacement. But what's mentioned above is all I've replaced so far.

Any ideas on what the gremlin(s) are is greatly appreciated! I do hear a click from the fuel tank when turning the engine key to on and it does start up without any problems. Thought about the catalytic converter being plugged but it only has 50,xxx miles and runs great until warmed up.
 
Hard to say the unburnt fuel would be raw gas left over as the engine rolled over when it shut off.it does sound like it is shutting off electronically. An component heats up opens the circuit and it shuts off. I would suspect the distributor in that one. Got no ida how to test one of them.
 
Fixed

Wanted to update on this issue that is now resolved. Still don't the exact fix since I replaced several things at once but I think the culprit was the ignition coil. It looked to be original.

Changing the plugs and wires did not fix it. Neither the coolant temp sensor although seemed to help a little. Ended up replacing the following which did fix it:

-Ignition Control Module (ICM) is under distributor cap
-Rotor Cap-only because it was easy to get to.
-Ignition Coil
-Idle Air Control Valve
-PCV valve
-repaired a vacuum line under the air box
-fuel filter
-MAP replaced

Again don't know for sure what fixed it but it was not throwing any codes prior to changing this stuff out. I think it was the Ignition Coil since it seemed to be the oldest part that was replaced.

Did discover that I may want to change out the TBI injectors-spray pattern not the best.

Now onto the AC system.
 
Have you checked the fuel pressure?

Sounds like a possible fuel pump dying, low voltage , bad grounds etc.

Throwing parts at it is bad start. Shop manual will have a good systematic diagnostic approach.
 
Agreed, throwing parts at it is not the best approach. However the ECC wasn't showing any trouble codes from the ECM so was at a loss where to begin-especially since I'm not familiar with this era technology. Shop manual by GM was essential for me and was well written. (not too technical) Fortunately, the parts I did throw weren't terribly expensive and the car seems to be running great again now. Do wish I knew exactly what the culprit was. Considered the fuel pump in the tank but since replacing that was a fairly big job for me I decided on the easier stuff first.
 
Agreed, throwing parts at it is not the best approach. However the ECC wasn't showing any trouble codes from the ECM so was at a loss where to begin-especially since I'm not familiar with this era technology. Shop manual by GM was essential for me and was well written. (not too technical) Fortunately, the parts I did throw weren't terribly expensive and the car seems to be running great again now. Do wish I knew exactly what the culprit was. Considered the fuel pump in the tank but since replacing that was a fairly big job for me I decided on the easier stuff first.

Problem is the early systems are more a management system than diagnostics'. People are so acclimated to the power of the new systems that they lack the knowledge or experience to start with the basic of diagnostic's. Watched a person spend half a day on a no start. Basic problem , tank was empty.
 
Fought one from st Lewis to Mitchell sd once it would run for a hour then just like you turned the key off die. Let it sit for 15-20 minutes and start right up run for another hr checked every thing could not find the problem. Finale figured it has to be the coil. Had a shop change it in Mitchell. When he took the old coil off the hei distributor half the the carbon rod that went threw the cap came with it. That was the problem. It took about a hr of drive time for it to heat up and open the gap to wide to fire. Never had another problem with it as long as i owned it. At least now you know what is new.
 
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