1992 F-150 4.9 Liter 5 Speed With Air conditioning

My first question is where is the PCM located on this vehicle? And is this the “computer”?

Decided to start a new thread. I have a 2 other post about problems with my truck. First it would not run after getting hot and then it would not start.

https://www.ford-trucks.com/forums/5...on-sensor.html

https://www.ford-trucks.com/forums/5...y-running.html

Decided to have it towed to the Ford dealership and they called yesterday and said that the PCM needed to be replaced. They said that it had stored a "Hard Fault Code", don't recall the exact words the service manager used but it had something to do with voltage. They said to correct this they had to replace the PCM at a tune of about $350. He also said there were other codes stored but they many a have caused by the voltage issue but no way to tell until they replace the PCM.

I want to believe the dealership as in one of my earlier post I described how my TPS was showing the incorrect volts. According to the manual it should be .05 to 1 volt at idle and 4 to 5 at full open. When I tested mine, it was it was negative 3.61 volts at idle and negative 0.30 at full open. Opposite of what the manual says the test should be and in NEGATIVE numbers. The new one I put on was the same. So my hunch is the TPS was OK.

I’m debating having the truck towed home ($50) and replacing the PCM (120) myself. Then seeing how it goes, if it is still bad hopefully I can drive it to the dealership and save another towing charge.

Any other thoughts and opinions are welcome.

Thanks
Bennie

 

The computer is easy to change out. It is located behind the kick panel on the drivers side (where the hood release is). Under the hood, you will see near the master cylinder is a bunch of wires going into one long plug with a single bolt through the middle. Remove this bolt. Go back inside the cab and pull the panel, you will see the computer, unscrew the hold down screws. Reverse for installation.
I had a '91 300/6 5spd 250,000 miles. started running rough and rich. Local shop put it on the scanner and was pulling all kinds of crazy codes. He said it was the PCM. I took it home and got a replacement from autozone and never had a problem for the next 50,000 miles when i traded it in on a '96 PSD dually.

 

that is not the way for a 92 and up computer.

you remove it through the engine compartment.

you need to unbolt the back of the inner fender to be able to pull it out.

 

Sounds like you lost the 5-Volt regulator in the PCM.
Yes the PCM is the main computer in your truck although there are a few other smaller computers that do other things, PSOM, ABS and Air Bag to name three.
They are also called modules.
That said the PCM Computer (AKA EEC, ECM) is not accessible from inside the truck.
You will have to take the drivers inter fender loose for clearance, take the plugs center screw loose and unplug it. There are two more small screws one on top and the other on the bottom of the PCM's plug and then you should be able to pull it out.
I would get the Program Code off the PCM and go to a salvage yard and get one out of the same year, engine, and transmission truck with the same Program Code. It should cost you about $40.00.

If you do not want to go the salvage yard route if you would post the Calibration Number, engine size and type truck (f150, f250) I will post the Ford part Number and you can take it to an Auto Parts Store and get one.

 

I was unable to find a match at any of the local salvage yards so I had to go out of state and they are shipping it UPS to me.

Any installation tips? Do I need to use some type of "grease" on the pins? Auto Zone sells some light bulb or wiring connection stuff, should this be applied to the pins?

I have heard that the computer must learn about your vehicle and it is necessary to drive it for a distance non stop at 55. How much truth is there in this?

Any other TIPS would be appreciated!

Thanks
Bennie

 

Putting grease on the pins is a good thing.
It takes about five miles for the computer to learn about most of your driving habits and the normal range of all of the sensors.
The computer is always learning about you and the sensors so there is not a set speed or a number of miles to drive it.
Just drive it at the speed you normally drive at. The first time you should drive it long enough to bring the engine up to normal operating temperature.