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Discussion Starter #1
Hello everyone,
I had an issue with my 02 F550 with 7.3L that was making me lose my mind (think of Clark W. Griswold and the christmas lights in Christmas Vacation). I finally figured it out and wanted to pass on the info to save someone else time with similar issues. So the symptom, random stalling for no reason while driving then crank no start. When cranking it would sound like it was trying to fire on a few cylinders. Sometimes it would fire and run for a few seconds then stall. Randomly would start and run fine for hours until you drove it.

During the crank start/stall I had 1800-2000 ICP pressure, cranking RPM 250-275, and 80 psi fuel pressure (would settle to 60 psi with the key off). I figured it was electrical with mechanical tests passing. I removed the CJB and used an oscilloscope to monitor the power to the PCM, IDM, and fuel pump to check for voltage dropping out. All passed, no loss of power to any part during the issue. Powers and grounds were load tested and voltage dropped with a halogen headlamp bulb and passed. Grounds were cleaned and triple checked in case there was a bad ground causing the electrical load to backfeed robbing the ground from another component (note previous owner had replaced the PCM, IDM, CJB, engine harness, and battery harnesses with new Ford components from the dealer a year ago for a random stalling issue). No issues found. I had just swapped the powertrain into this truck after it had been sitting for a year so I was thinking maybe it had something to do with the new truck since they were previously going after a random stalling issue. I dropped the tank, drained it, cleaned it out. Fuel was not discolored, no water separation, and passed flashpoint testing indicating it had not degraded and was not contaminated with something other than diesel. Fuel out of the bowl was a solid stream with no aeration. Injector buzz testing passed with no abnormal sounding injectors and no codes were ever present in any module. Batteries were newer NAPA legend AGM's and passed load testing. No loss of CMP or RPM signal during the event. ICP and IPR read normal during the stalling event with no drop out. No abnormal wave length from the alternator creating RF interference etc. For all intensive purposes, it should start and run with all of these tests passing.

Last night when it was acting up I noticed at times the injector buzz test would kick out early and would not complete. That was the first aha moment and the first time it would not complete the buzz test. I started by unplugging the bank 1 injector harness plug, truck started and ran without stalling on the cylinders on bank 2. Plugged bank 1 back in, boom back to start/stall again. It would not stay running with the bank 2 injector harness plug unplugged. I was thinking it was a shorted injector and pulled the bank 1 valve cover. During my inspection I found when the previous owner of my 7.3L replaced the UVC harness they routed the wires in front instead of behind the plastic pegs on the valve cover gasket. This caused the wiring to rub on the pushrod for cylinder 5 causing the random short taking the IDM down intermittently. The pushrod had to be in the right position to make contact creating the short which is why it would try to start but stall. If the connector was shifted slightly it would not short and it would run. Only when it shifted from bumps or engine vibration would it make contact again inducing the condition. If anyone runs into a similar situation, even if the injector buzz test passes with everything else passing it may help to disconnect one bank at a time to see if by chance you have an intermittent shorted injector or UVC harness that is not apparent during buzz testing.
 

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Gustafson
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9,178 Posts
Bravo!

This is an amazing write up and I thank you for posting it. I do not have a 7.3 but this is very good information for someone who does.
 

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Premium Member
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3,729 Posts
I have a 02 F350 7.3, I'm Diesel dumb so this information is very helpful. Thanks for taking the time to post it.
 

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What kinda scanner ya got, I had a similar issue on my 7.3 excursion and I bought a auto enguiniety and saw I had miss fires on one bank, that scanner is way smarter than me, turns out my glow plug wiring had melted at the Uvc connection and was grounding out from time to time. 7.3 is a awesome and simple engine but not fun to work on, especially in a excursion, my f250 is easier to get to things on. Good write up


Sent from my iPhone using Tapatalk Pro
 

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Discussion Starter #5
What kinda scanner ya got, I had a similar issue on my 7.3 excursion and I bought a auto enguiniety and saw I had miss fires on one bank, that scanner is way smarter than me, turns out my glow plug wiring had melted at the Uvc connection and was grounding out from time to time. 7.3 is a awesome and simple engine but not fun to work on, especially in a excursion, my f250 is easier to get to things on. Good write up


Sent from my iPhone using Tapatalk Pro
I am using the free FORSCAN program found online along with an OBDII adapter from Amazon. It works pretty well and does most of the tests I need.
 
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