Bad Computer?
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Bad Computer?
I have a 92 f150 with a 300 6 cylinder. Fuel pump would not stop running after turning on the key. It would start but ran extremely bad and burning alot of fuel. I found corrosion on the ignition control module so I replaced it. Now the pump shuts off like normal and runs much better but still no power and runs a little rough. The CEL is not on so cant pull any codes. I disconnected battery to try to reset but can't get anywhere. I took computer out and can't see anything wrong. Can anyone please help me out?
Fleet Owner
Joined: Aug 2005
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From: Easton,Ks
The ICM has nothing to do with the running of the fuel pump.
The CEL (MIL) does not have to be on to pull the codes.
Disconnecting the battery will erase any stored codes that you need to find the problem and may make the engine run worse if the computer was using a sensors stored value before a sensor went bad. Losing the stored value with a bad sensor can make the engine not start or run worse.
This is why you disconnect the battery only after replacing a sensor but not for replacing an actuator.
The CEL (MIL) does not have to be on to pull the codes.
Disconnecting the battery will erase any stored codes that you need to find the problem and may make the engine run worse if the computer was using a sensors stored value before a sensor went bad. Losing the stored value with a bad sensor can make the engine not start or run worse.
This is why you disconnect the battery only after replacing a sensor but not for replacing an actuator.
Fleet Mechanic
Joined: Nov 2011
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From: New York
Can you post a pic or two? Ideally of both sides of the circuit board. Almost every PCM of this era that I have opened up has at least one bad capacitor.
Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
If they are visibly leaking of course they are bad but plenty, maybe most, capacitors never leak. They are only a couple bucks to replace and aren't designed to last more than maybe ten years or so to begin with.
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I have a neighbor who is bringing his scanner to try to get a code. I replaced the ICM, TPS, IAC, fuel pump relay, and fuel pressure regulator. Running out of things to try. I will try to get pics posted. Not sure what the capacitors look like. Thanks for the help.
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Fleet Owner
Joined: Aug 2005
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From: Easton,Ks
A little late for the scanner after disconnecting the battery. The CM codes are lost and the CM codes is what tells you the most of what is going on.
The KOEO part will just test the electrical circuits to the sensors.
The KOEO part will just test the electrical circuits to the sensors.
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Just put a new pcm in the truck. CEL is not on, pump shuts off in 1 second, starts right up and idles fine but runs like crap. No power. Drove it back the driveway with accelerator to the floor and went 20 MPH. Getting very frustrated!! Any thoughts?
Fleet Mechanic
Joined: Nov 2011
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From: New York
Did you get the right PCM? Does the 3-4 character catch-code (exp, POP, POP2, C2M1) of the replacement match what you took out? Mind you, it doesn't have to match exactly. Tell us what came out and what went in.
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I took the old one in for a core exchange. My dad stopped and wrote down the numbers/letters on the old pcm since it was still at the auto parts. They got the numbers when they ordered the new one and told me it was pre programmed just plug it in. I will check the new one to see if numbers match. Do I need to unhook the battery to unplug it?
If it is the correct pcm, what else could be wrong?
If it is the correct pcm, what else could be wrong?
Lead Driver
Joined: Jul 2007
Posts: 7,868
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From: Rhode Island
Be careful with the numbers, there are quite a few numbers on the PCM, including a part number for just the PCM case itself - which many PCMs used.
The PCM should never be removed with the battery connected. If you can verify you have the correct PCM, I'd start by trying to pull the codes.
The PCM should never be removed with the battery connected. If you can verify you have the correct PCM, I'd start by trying to pull the codes.
Fleet Mechanic
Joined: Nov 2011
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From: New York
Have you verified that you got the correct PCM yet? Not all error codes will generate a CEL.
Fleet Owner
Joined: Aug 2005
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From: Easton,Ks
Another ground wire for the computer (G104), the case ground pin #20:
Not sure if I fully understand your question.
For a good working Computer no the CEL does not have to be on to check stored codes.
If you are asking if you just turn on the key and the CEL does not light up then NO you can not pull the codes as you have a problem with the computer most of the time.