Bad MAP Sensor Ground?
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Bad MAP Sensor Ground?
Having acceleration problems with my 1988 F350, 351W. Stumbles heavily at any attempt to accelerate. It was hard to start and sometimes did not start (esp when hot), but I think I've solved that problem by removing and cleaning the MAF. I have checked the vacuum (15" at idle) and fuel pressure (40 psi) and they seem to be in order. Checked for vacuum leaks and found none. Did find two of the throttle body vacuum port caps that were deteriorated and replaced them but no improvement.
I tested the original MAP sensor and it failed to consistently show decreasing frequency with increasing vacuum.. Next I tested ground through the sensor to the battery and got 7.5V. That's not right either, so I replaced it, thinking I had a slam dunk. But, no improvement in engine problems. Now I'm thinking grounding problem, so I check the 3 PCM grounds against the battery and consistently got 12.68V - spot on. I've also gone to all wiring grounds that I can find, checked them against the battery and cleaned up any that showed corrosion (4 total, 2 cab to frame and 2 radiator shroud to frame).
Now my frustration level is elevated and I'm out of ideas (not an uncommon condition for me). Any help would be appreciated.
I tested the original MAP sensor and it failed to consistently show decreasing frequency with increasing vacuum.. Next I tested ground through the sensor to the battery and got 7.5V. That's not right either, so I replaced it, thinking I had a slam dunk. But, no improvement in engine problems. Now I'm thinking grounding problem, so I check the 3 PCM grounds against the battery and consistently got 12.68V - spot on. I've also gone to all wiring grounds that I can find, checked them against the battery and cleaned up any that showed corrosion (4 total, 2 cab to frame and 2 radiator shroud to frame).
Now my frustration level is elevated and I'm out of ideas (not an uncommon condition for me). Any help would be appreciated.
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Joined: May 2006
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From: Central Mississippi
Did it ever throw a MAP code? When mine failed it would hardly run at all.
When I replaced, I went Duralast that failed 1 year later. Got a replacement, then picked up Motorcraft at JY & I ran that till a MAF upgrade.
I'd also open the ECU & look at the caps.
When I replaced, I went Duralast that failed 1 year later. Got a replacement, then picked up Motorcraft at JY & I ran that till a MAF upgrade.
I'd also open the ECU & look at the caps.
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Yes, you are correct - learning as I go. What I removed and cleaned was the idle air control valve. Yes, it has thrown code 22, but I'm going to read them again to see what shows now. I'm also reading where a bad IAC can cause the stalling problem - any way to test that with a DVM or by applying voltage?
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From: Central Mississippi
Looks like the majority of those are too high reference voltages of some sort. Don't know if you have a pwr steering switch (52) most 351 I don't think have them.
The (98) I find is "electronic pressure control driver open" if it has an E4OD & a hard ecu fault if it doesn't.
Still think you should open up the computer/ecu & look for leaking capacitors. Think acid out of dead batteries on the circuit board.
Causes all sort of havoc operation.
The (98) I find is "electronic pressure control driver open" if it has an E4OD & a hard ecu fault if it doesn't.
Still think you should open up the computer/ecu & look for leaking capacitors. Think acid out of dead batteries on the circuit board.
Causes all sort of havoc operation.
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Pulled the ecu and here is a picture. Looks clean to me, and the blue capacitor doesn't appear to be bulged on top, but I'm no expert. Can you detect anything out of sorts? My tranny is the ZF 5, so code 98 might be a hard ecu fault?
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Logistics Pro
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From: Mexico, Missouri
The Blue capacitor looks suspicious. I can't enlarge the picture enough to see the fuzzy white stuff under and surrounding it.
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I have access to a 1990 F350 (460 V8) free of charge, is it worth the trouble to substitute it for the '88 ecu to help determine if it is bad? I understand that I have to take it to the dealer to get the VIN written to it (assuming I can find a dealer who will do it)?
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Joined: Oct 2005
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From: Kentucky
That 1990 PCM will work as a suitable test/replacement as long as it has the same transmission as yours. There is no programming for this vintage PCM. The VIN is not tied to the PCM in any shape or form.