3800 C - Misses When Hot

1989 LeSabre T-Type, 3800 C motor, starts up fine cold, but after warming up, starts to miss and runs rich. Runs worse after a short sit then restarted. Yesterday, it got so bad I could start the car, but it would not run until it cooled off.

First off, new parts (within past year or two).
Plugs, wires, coil, module, EGR, MAF, timing chain/gears/tensioner, cam position magnet, harmonic balancer, PCV, oil pressure sensor, cat, muffler.

Notes:
There are no codes present or stored.
Checked and tightened suspect connectors.
All wires have same resistance when hot.
All plugs are clean after warmed up.
Fuel pressure regulator has good vacuum.
Knocked the crap outta the IAC so it's not clogged.
All injectors are firing, hot or cold.
Coil terminals have equal resistances when hot.
Used a snap-on scan tool to read all sensors, all check out ok.
Fuel pump and crank sensor are original. Fuel filter was changed in Feb 2004.
Coil and module were changed a month ago.


After some research, I can almost surely say that something electrical is getting too hot and giving bad signal or no signal at all. I've come to a few possible conclusions:
1. Fuel pump loses ability after getting hot.
2. Module is bad.
3. ECM is going bad.
4. Crank sensor is broken and reads improperly at operating temp.

Any help would surely be appriciated. :smile:

1989 LeSabre T-Type, 3800 C motor, starts up fine cold, but after warming up, starts to miss and runs rich. Runs worse after a short sit then restarted. Yesterday, it got so bad I could start the car, but it would not run until it cooled off.

First off, new parts (within past year or two).
Plugs, wires, coil, module, EGR, MAF, timing chain/gears/tensioner, cam position magnet, harmonic balancer, PCV, oil pressure sensor, cat, muffler.

Notes:
There are no codes present or stored.
Checked and tightened suspect connectors.
All wires have same resistance when hot.
All plugs are clean after warmed up.
Fuel pressure regulator has good vacuum.
Knocked the crap outta the IAC so it's not clogged.
All injectors are firing, hot or cold.
Coil terminals have equal resistances when hot.
Used a snap-on scan tool to read all sensors, all check out ok.
Fuel pump and crank sensor are original. Fuel filter was changed in Feb 2004.
Coil and module were changed a month ago.


After some research, I can almost surely say that something electrical is getting too hot and giving bad signal or no signal at all. I've come to a few possible conclusions:
1. Fuel pump loses ability after getting hot.
2. Module is bad.
3. ECM is going bad.
4. Crank sensor is broken and reads improperly at operating temp.

Any help would surely be appriciated. :smile:




Try a new oxygen sensor and then do fuel pessure test,you said you have good vacuum at the pressure regulator but did you check for fuel in the vacuum line before starting?

Try a new oxygen sensor and then do fuel pessure test,you said you have good vacuum at the pressure regulator but did you check for fuel in the vacuum line before starting?

Oh yeah, forgot, O2 was replaced in August. Any other ideas?