94 ford f150 5.0.

Truck runs well. After a time, it loses power and barely idles. Will not rev up. Extreme lean smell from exhaust.

If I disconnect the maf, truck will start and run. Then it surges and gets poor fuel economy. Have checked tps voltage and that's good. Egr functions properly.

Have replaced maf several times with the same result. Power and ground remain the same. When working, signal shows battery voltage. As its accelerated, voltage goes down. When it dies, I detected .1 volts.

what does fuel pressure look like when it bogs down

Your MAF voltages are very strange. :dry: The signal wire should never show battery voltage, or decrease with airflow. Do you recall which wire you were probing, specifically?



It kinda sounds like it's struggling for fuel once it's in closed loop. Any chance you could pull codes, or run the KOEO Self-Test?

Fuel pressure is unchanged. We also tested for vacuum leaks by smoking the intake. None found.

It's not a closed loop or open loop symptom. I had it run 100 miles without a problem, then it died in the middle of downtown Seattle. Cannot run codes. I have tried 2 scanners without result. May be they are old and not working. My new scanner will not run OBD I.

More to come shortly.

Red wire is battery voltage with ignition on. Black with white tracer is ground.
Tan with light blue tracer is computer ground. Light blue with red tracer is the signal that changes with acceleration when functioning properly. It also shows .1V when the malfunction occurs. Again, this wire shows battery voltage at idle and goes down with acceleration.

plugged exhaust??

Exhaust is fine. It wouldn't run well plugged in if the exhaust was an issue.

I have even replaced the capacitors in the ECU