I have been working on an older gentleman's very-well taken care '89, F-150, 351. He called to tell me he was driving the truck, with no problem's and approached a light, and as he came to a stop, it started to running rough, as if it were out of gas. Upon, feathering the accelerator, he made it to another light, then it died. Got it running again, terrible idle, choking itself almost. He got it home and I ran codes. Only got 31, for EVP. Ran engine runing test, and got 22, 42. I knew 42 was Rich condition, but didn't expect MAP sensor. Went and grabbed spare MAP sensor, known to be good. It stayed running, though better than before, but still poor and we re-ran Engine running test. Same code for MAP sensor. My question is if I replaced the MAP sensor with known good one, shouldn't that have eliminated that code?

Still have to check fuel pressure, but so far, these are known items that have been repaired or replaced since life of truck. New water pump 4 years ago, w/new t-stat, new radiator, last year, O2 was changed 3 years ago, the EGR, TPS was changed 2 years ago, new plugs, cap, rotor, wires, ECT last year. I had him disconnect the neg. battery cable and he left it overnight and haven't heard from him, but will tonight on outcome of truck. I told him to drive it some on their street, since very little traffic and if problematic, he can pull back into driveway.

Anyone have any other advice or input before I start chasing gremlins? I suspect ECM but not pulling it yet until I check fuel pressure. No fuel in the FPR. I check vacuum line running to both FPR and MAP sensor, both good, no leaks. Still got to check for feedback from O2 sensor to rule it out.

 

No.. codes do not just go away they have to be cleared from memory.

Fuel pressure is my suspect.

 

Unless the ECM is dying........(internal ground(s) problem on the PCB)

Bob

 

With the engine running, disconnect the MAP sensor for a minute and see if the idle improves. If it does, you may have another bad MAP sensor. Also, remove and clean the IAC and have a spare gasket on hand.

 

Owner called today, said it exhibited same problems as yesterday. He drove it as I said to do so, and will find out tonight. I will know more since he scheduled it for local shop to diagnosis it and will update this when they are finish.

Thanks for everyone's input.