fomoco998

All I know is while driving at any speed my truck would die with foot to the floor then recover and run normal then repeat itself. Start up and stall. I figured it was due to computer switching to limp mode. All related to air fuel. I've been mechanic for 40+ years and this is my first encounter having this problem and it being the oxygen sensor and nothing more. Maybe I'm misunderstanding the symptoms. When my check engine light would come on the truck would recover and run normal.

lockingnut

I don't even have to be in the truck and it dies. In the past it's died out on the highway, or sitting at a light. It's died at operating temperature, and more recently dies cold. I go no problem trying the Oxygen sensor, I'm at the point of trying everything.
I haven't messed with the error codes yet, I had hoped Ford did that the last time I had them look at it. They told me there were no error codes showing when it was towed in. They replaced the ignition switch on the column (at my request) and thought that was it. It idled for an hour, a tech took it out on the highway and it did fine. I picked it up and it didn't make it to my house 4 miles away.
I'll do the oxygen sensor like you suggest. And I'll look at the codes. and go from there.

Thanks,
Don

fomoco998

My reply was for original poster Bean Counter and you possibly have a different problem. Just unplug the oxygen sensor to put truck in limp mode and not be switching back and forth and see if it changes things. Your check engine light will stay on. Your problem sounds a little different due to you have no check engine light or codes. Usually computer related problems show a code. Fuel and ignition is different.

lockingnut

So sorry. Guess I should've started my own thread.
Thanks, I'll try what you say.

Don

Bean Counter

Lockingnut - ECM (Engine Control Module) and PCM (Powertrain Control Module) are sometimes interchanged. I believe that Ford called the units ECMs before they integrated electronically controller transmissions; after adding those, they went to PCM so that it encompassed more than just the engine.

Fomoco998 -The O2 sensor was one of the first items that I replaced as I was getting the truck to pass its emissions test. All of the wires leading to it appeared to be in good shape and I've gotten no codes indicating an issue with the sensor.

The only item I haven't replaced at this point is the PCM/ECM and, given what the truck did when it went into fail-safe mode, I'm really suspect that said unit is the root of my issues.

Thanks,
David

Bean Counter

I finally had the time to work on the truck this morning. I picked up a remanufactured control module (ECM/PCM) from Rock Auto and 20 feet of silicone vacuum hose along with the two tees. Replaced all of the vacuum lines - took less than half an hour - and installed the new module.

The result? It behaves like a totally different truck. The check engine light is still coming on so I still have some more diagnostic work to do but it idles incredibly smooth at about 600 RPM (even with the AC on) and doesn't cut out. Acceleration is good (at least as good as it ever was for these trucks). I'm keeping my fingers crossed that I've finally gotten the truck to the point of being reliable.

Next up is dropping the rear tank and replacing the fuel pump in it. After that, this beast might need to go on a trip......

qdeezie

A bit of a redundant question, but did you disconnect the battery to clear the codes after replacing the vacuum hoses and ECM?

Bean Counter

That's a GOOD question! I had the battery disconnected during the entire process but will do it again today and see what happens.

hstaple1979

Yeah, you should have. Why people feel it necessary to hijack a thread to get a problem solved is beyond me. Be courteous, not what you just acted like. I for one wouldn't help you because of this behavior.

Bean Counter

Small update - I did disconnect the battery to reset the error codes. Got in, fired up the beast and the check engine light came back on again . Same codes - 22 and 34. The truck is running really well which is what is perplexing me the most. I think, at this point, I may find a professional to take a look at it. Otherwise, I'm going to have to get used to that stinking light! I can certainly live with the light if the truck continues to run well - I just hate not being able to solve the puzzle.

Thanks for all of the advice everyone, especially Qdeezie. If I ever figure this out, I'll let everyone know what the solution was.