MAP failure mode
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5th Wheeling
Joined: Dec 2013
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MAP failure mode
I just rebuilt the power train on my '90 F250 5.8L E4OD, and everything was great for a couple of weeks, then the truck started bucking, stalling, and going in and out of "limp home" mode. One of the recurring codes was 22, even though the KOER test would not complete.
After sitting a couple of days KOEO showed only code 11, and KOER showed codes 44 and 33. I checked the EGR, and it seems to work properly. i have removed the air pump, but the relay is still there, so code 44 is a mystery. Today, after a 20 mile drive the truck started bucking again, and KOEO shows code 22, so I hooked a scope up to the MAP sensor.
With the engine not running, I see a 158 Hz square-ish wave. With the engine running the output occasionally drops out to just a flat line. I checked VREF, and it appears solid.
So, does this sound like a MAP failure. The sensor is brand new, so it seems odd. I also ordered it from Rock Auto, so exchanging it is not as simple as taking it down to the local auto parts store.
After sitting a couple of days KOEO showed only code 11, and KOER showed codes 44 and 33. I checked the EGR, and it seems to work properly. i have removed the air pump, but the relay is still there, so code 44 is a mystery. Today, after a 20 mile drive the truck started bucking again, and KOEO shows code 22, so I hooked a scope up to the MAP sensor.
With the engine not running, I see a 158 Hz square-ish wave. With the engine running the output occasionally drops out to just a flat line. I checked VREF, and it appears solid.
So, does this sound like a MAP failure. The sensor is brand new, so it seems odd. I also ordered it from Rock Auto, so exchanging it is not as simple as taking it down to the local auto parts store.
Logistics Pro
Joined: Mar 2005
Posts: 4,698
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From: Mexico, Missouri
Different error codes and then passing, failing tests leads me to believe the PCM is failing.
Check the 5vdc reference voltage for fluctation and spikes. Capacitors failing after 20+ years is a given.
Pu the PCM and look for leaking capacitors.
Check the 5vdc reference voltage for fluctation and spikes. Capacitors failing after 20+ years is a given.
Pu the PCM and look for leaking capacitors.
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5th Wheeling
Joined: Dec 2013
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I did wonder about the PCM. It is, after all, 27 years old. I did monitor VREF and did not see it drop, but my failure is erratic.
Is there a thread for refurbishing the PCM? I would probably replace all the caps at once and would order them if I had a list.
Is there a thread for refurbishing the PCM? I would probably replace all the caps at once and would order them if I had a list.
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5th Wheeling
Joined: Dec 2013
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Answering my own question:
Capacitor Repair: Ford A9L ECM « Moates Support
Looks like 4 47 uF 16V caps.
Capacitor Repair: Ford A9L ECM « Moates Support
Looks like 4 47 uF 16V caps.
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From: Rhode Island
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5th Wheeling
Joined: Dec 2013
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I've put in for a replacement MAP under warranty. Meanwhile, I pulled my PCM, and I'll probably replace the caps. Mine has only a 3.3uF 63V and a 47uF 10V. They don't look bad, but age does take its toll.
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5th Wheeling
Joined: Dec 2013
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Quick update. I have been out of town for the last week and not able to do anything, but today I took it for a drive in the heat, and things are different. The truck ran perfectly until I stopped, turned it off for 10 minutes or so, and then started it back up. Then, the CEL came on, it had no power, and it would hardly move -- I think the transmission was in 3rd gear. I was in a parking lot, so I dropped the transmission to L, and it moved better, then after a minute or so things came back to normal, so I went to my next stop without issue, left the truck running, and then went to my third stop closer to home and turned it off for a few minutes. When I started it back up, it was back to no power and would hardly move. I nursed it back home, where I attempted to get some codes from the computer.
Now, I am unable to get the computer into test mode. I put the jumper on the connector, and it makes no difference -- engine off or engine on is just like the jumper is not connected. Also, I noticed the fuel pump runs all the time, which my research indicates is the PCM. So, I'm now researching where to get a replacement PCM and which one I should get.
Now, I am unable to get the computer into test mode. I put the jumper on the connector, and it makes no difference -- engine off or engine on is just like the jumper is not connected. Also, I noticed the fuel pump runs all the time, which my research indicates is the PCM. So, I'm now researching where to get a replacement PCM and which one I should get.
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5th Wheeling
Joined: Dec 2013
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Just to button this up. I ordered a PCM from Advanced Auto, part number 78-4436, put it in and so far, so good. With the web discount and some other savings it only cost me about $60. The new PCM passes the KOEO, but KOER gives me a code 33 (EGR) that I am not able to explain. No CEL, and no other indications of problems.
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tmcm
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Dec 21, 2005 07:01 PM