Another bad PCM?
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Another bad PCM?
Howdy folks,
I have a 1996 4.9L straight 6, and I just replaced the PCM yesterday. I did this because I was getting three O2 sensor heater malfunction codes. I thought it was odd that 3 would go bad at once, so I went through the diagnostic procedure in the Ford service manual. The heater circuits checked out fine, so I got to the step "replace PCM". After some reading here on the forums and the results of the test, I was pretty confident it was the PCM after all and not something else. The O2 heater malfunction went away with the new PCM, however, after replacing the PCM, the check engine light came on AGAIN after driving some. This time it gave me code P0443 - EVAP purge valve malfunction.
I ran through the diagnostics in the Service manual again, and the purge valve seemed to check out fine, and the manual brought me to the "replace PCM" conclusion again.
Could the new PCM possibly be bad also? Or could there be something in my truck causing the computer to go bad? I find this strange.... Is there some other circuits I should check?
Any ideas? Thanks!
I have a 1996 4.9L straight 6, and I just replaced the PCM yesterday. I did this because I was getting three O2 sensor heater malfunction codes. I thought it was odd that 3 would go bad at once, so I went through the diagnostic procedure in the Ford service manual. The heater circuits checked out fine, so I got to the step "replace PCM". After some reading here on the forums and the results of the test, I was pretty confident it was the PCM after all and not something else. The O2 heater malfunction went away with the new PCM, however, after replacing the PCM, the check engine light came on AGAIN after driving some. This time it gave me code P0443 - EVAP purge valve malfunction.
I ran through the diagnostics in the Service manual again, and the purge valve seemed to check out fine, and the manual brought me to the "replace PCM" conclusion again.
Could the new PCM possibly be bad also? Or could there be something in my truck causing the computer to go bad? I find this strange.... Is there some other circuits I should check?
Any ideas? Thanks!
Last edited by bigcountry350; Jun 3, 2007 at 10:23 PM.
Post Fiend
Joined: Mar 2002
Posts: 19,402
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From: Bonita Springs FL
The Ford service manuals want you to replace the PCM a lot. In reality, the PCM rarely goes bad, so the original you replaced was probably fine to begin with.
I wish I could weigh in more on the code you're getting, but I haven't had to deal with that one myself.
I wish I could weigh in more on the code you're getting, but I haven't had to deal with that one myself.
FTE Chapter Leader
Joined: May 2006
Posts: 12,342
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From: Central Mississippi
Weak grounds? Chaffed wires? Loose pins or corrosion in the connectors?
What kind of mileage, use (an easy life or rodehard/put up wet) & overall shape of your underhood enviroment?
What kind of mileage, use (an easy life or rodehard/put up wet) & overall shape of your underhood enviroment?
Junior User
Joined: Jan 2007
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From: Middle of Ohio
after my 96 went in the shop to get the pcm replaced we got it home and found that chafed wires by the clutch spring under the dash which is why it kept poping the fuse and shorted out the o2 sensor circut hah funny huh?
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Scndsin
I have a little over 63K on it. Not bad for a '96 huh? I use it daily to run around, not much heavy duty hauling.
As far as the O2 heaters, I don't have that problem since I changed the PCM. I just have the P0443 code now... I didn't have that one before... The connections from the PCM connector to Purge valve checked out fine. I'm getting the correct voltage also.
I guess I'll have to dig deeper into the wiring.... Maybe there is a bad connection unrelated to the Purge value and it is causing a bogus reading? :\
I wouldn't be in a big hurry to get this fixed, but I'm moving and I will have to pass an emmissions test. I'm not sure if they will reject me for this... Anyone know how strict Arizona is?
I have a little over 63K on it. Not bad for a '96 huh? I use it daily to run around, not much heavy duty hauling.
As far as the O2 heaters, I don't have that problem since I changed the PCM. I just have the P0443 code now... I didn't have that one before... The connections from the PCM connector to Purge valve checked out fine. I'm getting the correct voltage also.
I guess I'll have to dig deeper into the wiring.... Maybe there is a bad connection unrelated to the Purge value and it is causing a bogus reading? :\
I wouldn't be in a big hurry to get this fixed, but I'm moving and I will have to pass an emmissions test. I'm not sure if they will reject me for this... Anyone know how strict Arizona is?
Lead Driver
Joined: Feb 2003
Posts: 8,140
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From: Oak Harbor, OH
So there is a sensor on purge valve or it's electric? It's probably bad. It was posted here sometime before that something in the neighborhood of 90% of all pcms that are sent in to be refurbished are fine, nothing wrong with them at all. It's more likely in the grounds.
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Fleet Owner
Joined: Aug 2005
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From: Easton,Ks
Originally Posted by pfogle
So there is a sensor on purge valve or it's electric? It's probably bad. It was posted here sometime before that something in the neighborhood of 90% of all pcms that are sent in to be refurbished are fine, nothing wrong with them at all. It's more likely in the grounds.
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Pin 56
I checked the connection at pin 56, and the resistance was in the specs (between 30 and 38 ohms). I measured 34.4 ohms. I will continue checking things out tomorrow or maybe Wed....
Cool diagram
Cool diagram
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Vacuum leak
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