351W fuel injection problem
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Joined: Oct 2006
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From: Tullahoma, TN
351W fuel injection problem
The 351W in my 1991 F250 has suddenly started idling & running poorly. I have done the diagnostic code down load and there are no codes. After talking with a friend, I bought an infrared temperature gun and it appears that cylinders 2,3, 6, and 7 are not firing (exhaust manifold is cold). I was able to reach the #5 and #6 injector wiring connectors and unplugged them and plugged in a troubleshooting light - on #5 the light flashed, on #6 the light did not come on. Reading through some Ford fuel injection books, I think that the #1,4,5,& 8 injectors fire together and the # 2,3,6, & 7 injectors fire together. Does anyone have any ideas about what I should do next? Thanks.
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Joined: Jun 2004
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From: Central NY
You are correct in the batch firing order. It does sound like you have an open in the harness or a bad pcm.
The computer fires the injectors by providing ground so You should see +12v on the common line at the injector. Use a volt meter rather than a testlight.
If you have 12v then you need to check out the wiring back to the eec and check continuity beftween those 'bad' injectors and the eec. Pin 59 controls injectors 2,3,6,7. Pin 58 controls the remaining injectors. If you have continuity back to the eec connector then you might have some corrosion in the eec conector, clean it up the best you can and test again. If it still won't fire 2,3,6,7 then it looks like its time for a rebuilt/used computer.
The computer fires the injectors by providing ground so You should see +12v on the common line at the injector. Use a volt meter rather than a testlight.
If you have 12v then you need to check out the wiring back to the eec and check continuity beftween those 'bad' injectors and the eec. Pin 59 controls injectors 2,3,6,7. Pin 58 controls the remaining injectors. If you have continuity back to the eec connector then you might have some corrosion in the eec conector, clean it up the best you can and test again. If it still won't fire 2,3,6,7 then it looks like its time for a rebuilt/used computer.
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New User
Joined: Oct 2006
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From: Tullahoma, TN
Actually, I did a voltage check too on #6. I got 12v on both pins, which did not make any sense at all. I'll try to disconnect the main harness from the ECM and do some continuity checks on the harness & check for corrosion.
Posting Guru
Joined: Jun 2004
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From: Central NY
Yes that is correct if one of the four injectors are plugged in. There is a coil in each injector, when the eec grounds out one side, current passes thru the coil causing the injector to "fire' very much like a relay. If you don't know electronics well, a coil is just a series of loops in a wire, basically a short-circuit to dc voltages.
If you have 12v at pin 59(with the injectors plugged in then you know the wiring is parially good (continuity from at least one of the four injectors) so now the problem is down to the eec connector or the eec itself.
I wonder if you have a local junkyard that would let you try out an eec.
If you have 12v at pin 59(with the injectors plugged in then you know the wiring is parially good (continuity from at least one of the four injectors) so now the problem is down to the eec connector or the eec itself.
I wonder if you have a local junkyard that would let you try out an eec.
Hotshot
Joined: Jul 2002
Posts: 14,285
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From: Bend,OR
how did you try pulling codes. did you use the procedure from www.fordfuelinjection.com you should see at least 1 code
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