1992 F-150 4.9 Liter 5 Speed With Air conditioning

Truck was having all kinds of problems so it was taken to the dealership to have them troubleshoot it. They determined the PCM needed to be replaced, and they quoted $350. for parts and labor. My previous post can be found here.

https://www.ford-trucks.com/forums/6...ol-module.html
https://www.ford-trucks.com/forums/5...on-sensor.html
https://www.ford-trucks.com/forums/5...y-running.html

I decided to purchase the part at a salvage yard and replace it myself. Was unable to find one locally so searching the Internet one was found at it arrived today.

My code is F2TF - APB (my calibration code is 2-51F-R00) but the one I received is F2TF - ATB. The local salvage yard had given me a copy of their interchange listing and it list F2TF – APA and F2TF - ARB as interchanges. Since the one I received did not match any of these, I called the folks that shipped me the part and they said their book does show it will and to give it a try and let them know if I have problems.

I did not like the sound of that so I stopped by the dealership and talked to the parts guys about this. They looked up the one I received and confirmed that it is for the same truck but it is for a different calibration code. A mechanic was at the parts counter and joined in the conversation and said 9 out of 10 times the PCM will work but could throw out codes for a sensor it is looking for the could be in that calibration code but not in mine. Said I could not hurt anything by trying it so I decided to try it.

The truck still will not start. It is doing basically them same thing that I took it to the dealership for in the first place which is cranking but not starting. I can smell gas from under the hood but when I let it crank for a while nothing happens and when I release the key, it acts like it want to rumble to life, but just for a second or 2.

What is the likelihood that the truck will not start because I have the wrong PCM?

Since I have the same problem with my PCM and this replacement PCM, could there be something else going on?

Also today when I turned to key to start it, all I got was a “thunk". But when I connected the terminals at the starter relay it cranked. The battery is brand new, just got it today and the negative battery cable was replaced within the last 12 months. What could be causing this?

Thanks
Bennie

 

I was thinking ignition switch, does the cluster light up and everything when the key is in On?

I agree with the mechanic, it should run on most pcms, just not as well as it could.

So you have the starter turning over, and fuel pump pumping and the injectors firing. That leaves you with air and spark. Pull off the throttle body and give it a througho cleaning, also scrub out the IAC. Then barrow a coil or spark tester or timing light and check for spark. The timing light will be helpful in diagnosing the TFI module.

 

the ECU is ok. Since you say it seems like it wants to rumble to life after you let it crank for awhile change the plugs on her. Once plugs get wet they are basically junk especially if you've been having the prob for awhile. Cheap and easy to change the plugs. I had the same problem awhile back and that's what i did and she started right away




Jim

 

When I turn the key to the start position with the lights on (dash and headlights), the lights stay on. The only thing I notice usual is the speedometer needle will go backwards from zero slightly.

One other time when I had the problem of turning the key and hearing a “thunk” I think all the lights would go dim or completely off. I think that was caused by a bad negative battery cable.

As for the truck acting like it wants to rumble to life, I had the same situation before I was told the PCM was bad. The plugs are 1 to 2 years old with 20 to 30 thousand miles on them.

 

if you smell gas....it's flooded and the plugs are soaked.......and with 20-30k on them could be a big part of the problem...pull them and see how they are burning....different colors and deposits tell you things. Check the Haynes for pics of plugs. If even one of them has fouled out it can cause it not to start or run rough. I had one plug in a 350 fouled and it would barely start and idle....cleaned it and it was normal again.

Is the rest of your ignition system fairly new?...wires, coil, dist. cap, rotor, timing.....any wires crossed?......it honestly sounds like a tune-up issue to me but if you've covered all that........I'm as lost as you.

Good Luck

 

First off do not worry about the part number, the key is the program code.
If they have the same program code it will operate the same, as it will be running on identical programs. A program code may cover more than two or three years one way or the other.

If you do not know about program codes go to this URL:
http://fordfuelinjection.com/?p=17

That said starting a truck has very little to do with the PCM. The only thing the PCM does while cranking is turn on the Fuel Pump(s) and fire the injectors.

You say you smell fuel while cranking so the PCM is not stopping it from starting and the PCM that came with the truck is more than likely as good or better than the one you bough.

The people that rebuild PCM say that 85% of PCM that are sent in for repair that there is nothing wrong with them.

You can take the PCM out, leave it on the bench and spray starting fluid into the throttle body and it should fire and run for a second or two.

Make sure you have good spark while cranking (the PCM does not control it) and the injectors are firing (the PCM does this).

If you have spark try holding the throttle on the floor while cranking and see if it will start, this turns off the injectors and may start if you have a too rich to start condition.