1993 F250 bad PCM? Symptoms
#1
1993 F250 bad PCM? Symptoms
I am new to these forums and have a question regarding my 1993 F250. My truck has always ran like a top. My problems started about a week ago. I was driving and suddenly lost power (as though my truck was in limp mode). The check engine light turned on, engine sputtered (some exhaust smoke which smelled heavily of gas), transmission would not shift out of whatever gear it was in. I limped the truck back home and checked for codes. I tried jumping the connectors and hooking up my obd1 Ford code reader. nada.. No codes. The reader just showed zeros and would not perform any engine tests etc. (even with a check engine light) The next morning I start the truck and it runs, drives, and shifts perfect. About 10 min into my drive same sequence of events happens.
Also, either of my fuel pumps will run continuously when the key is in the on position. The transmission also shifts hard into park/drive (when it would start). I purchased a used PCM on ebay and replaced and truck now just cranks and will only fire for a second of two before stalling. It seems as though this problem gradually got worse. The fuel pump will not run with the PCM disconnected. I am beginning to wonder if the second PCM was good.
Any thoughts or input would be greatly appreciated.
Also, either of my fuel pumps will run continuously when the key is in the on position. The transmission also shifts hard into park/drive (when it would start). I purchased a used PCM on ebay and replaced and truck now just cranks and will only fire for a second of two before stalling. It seems as though this problem gradually got worse. The fuel pump will not run with the PCM disconnected. I am beginning to wonder if the second PCM was good.
Any thoughts or input would be greatly appreciated.
#2
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#5
Thanks for the reply.
Interesting- I had not thought of TFI and PIP module.
I am curious which of the following could cause my fuel pump to run continuously with the key in the on position..
bad TFI/PIP module, EEC relay, or bad PCM.
Not being able to check or receive any codes while my check engine light is on also baffles me.
Interesting- I had not thought of TFI and PIP module.
I am curious which of the following could cause my fuel pump to run continuously with the key in the on position..
bad TFI/PIP module, EEC relay, or bad PCM.
Not being able to check or receive any codes while my check engine light is on also baffles me.
#7
EEC relay or PCM. I'd try the relay first since it's easiest to swap - I always have a spare in the glovebox.
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#9
That said, I agree that the additional symptoms point to the PCM as the culprit. My suggestion was based on the premise that he should have a spare PCM relay in the glovebox regardless.
#10
The PCM relay only supplies power to the coil of the fuel pump relay. It can not turn the fuel pump off and on. It can keep the fuel pump from running if it does not supply power to the coil of the fuel pump relay with the key on. But then nothing else would run either.
A stuck closed Fuel pump relay can keep the fuel pump running with the key off.
A stuck closed Fuel pump relay can keep the fuel pump running with the key off.
#11
The PCM relay only supplies power to the coil of the fuel pump relay. It can not turn the fuel pump off and on. It can keep the fuel pump from running if it does not supply power to the coil of the fuel pump relay with the key on. But then nothing else would run either.
A stuck closed Fuel pump relay can keep the fuel pump running with the key off.
A stuck closed Fuel pump relay can keep the fuel pump running with the key off.
The relays cost next to nothing, and it's a good place to start rather than dropping $150 on a new computer.
#13
Thanks guys for all your input.
I did try swapping the regulators out (pcm and horn) and the fuel pump continues to run non-stop with the key in the on position. Both computers I have appear completely fine inside and they both have the same exact tuning code.
I feel like the fuel pump running non-stop, check engine light (with no readable codes), transmission stuck in gear, and now truck won't start should all lead to one problem. Anymore advice or anything else that could cause these problems?
I did try swapping the regulators out (pcm and horn) and the fuel pump continues to run non-stop with the key in the on position. Both computers I have appear completely fine inside and they both have the same exact tuning code.
I feel like the fuel pump running non-stop, check engine light (with no readable codes), transmission stuck in gear, and now truck won't start should all lead to one problem. Anymore advice or anything else that could cause these problems?
#14
Everything you post points to a bad computer.
You say the fuel pump does not run with the computer unplugged. So you know it is the computer turning on the fuel pump. You also know from this that the computer has a good ground. The only way the computer would be not at fault is if the computer was being reset over and over with the key in the run position. I have seen this with a 5.0L engine with bad wiring to the O2 sensor but I do not know what engine you have.
Even if the fuel pump relay was stuck closed making the fuel pump run all the time this would not stop it from starting and running.
Beside you know the fuel pump relay is working and the fuel pump relay coil wire is not shorted to ground or the fuel pump would not quit when you turn off the key.
You say the fuel pump does not run with the computer unplugged. So you know it is the computer turning on the fuel pump. You also know from this that the computer has a good ground. The only way the computer would be not at fault is if the computer was being reset over and over with the key in the run position. I have seen this with a 5.0L engine with bad wiring to the O2 sensor but I do not know what engine you have.
Even if the fuel pump relay was stuck closed making the fuel pump run all the time this would not stop it from starting and running.
Beside you know the fuel pump relay is working and the fuel pump relay coil wire is not shorted to ground or the fuel pump would not quit when you turn off the key.