robp823 Posted June 10, 2010 Share Posted June 10, 2010 08 F-550,45,000 miles.P0208 Injector circuit open cylinder 8.No other DTC's.Truck runs like crap.Feels like it miss's on more than one cylinder(multiple).Updated PCM first off.Watching SFT's nothing changes they all stay at 0.Never seen that happen.Followed PPT P.Had me check injector power and ground circuits.Checked from PCM connector E to UVC harness connector at Cylinder head.Both circuits Ohm out good.Removed the UVC harness right out of head and ohmed out good.Checked injector,good.Now i triple checked myself on this.Its telling me to replace the PCM.So i contact hotline.They tell me to replace the UVC harness first before condeming the PCM.So i ordered one and will put it in tommarow.Im puzzled because i ohmed tested like 3 times and even checked it over visually by taking the plastic cover off and found nothing.But on the other hand The way it is missing and why SFT's arent changing makes me think maybe it is the PCM.Anyone run into anything similar? Quote Link to comment Share on other sites More sharing options...
BrunoWilimek Posted June 11, 2010 Share Posted June 11, 2010 Ohm testing is not always reliable. As long as one strand of wire is intact, it will read OK. Load testing the circuit, or voltage drop testing is more reliable to detect problems. I use an old backup alarm as an audible circuit tester. Other techs use a headlamp bulb or foglamp bulb as it draws a significant amount of current and if the bulb won't light or only glows dimly, you know you have found the problem circuit. Also note(disregard this if you already know it)that you should never force probes in the end of connectors as this may spread the terminals, actually causing more problems than you started with. Always backprobe the wires. Snap-On sells a set of 3 pin-style tips to backprobe wires without damaging terminals or puncturing insulation. Note: hotline is not always correct, it still sounds like a possible PCM to me, especially with the other things you mentioned. Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted June 12, 2010 Share Posted June 12, 2010 Also note(disregard this if you already know it)that you should never force probes in the end of connectors as this may spread the terminals, actually causing more problems than you started with. Always backprobe the wires. Snap-On sells a set of 3 pin-style tips to backprobe wires without damaging terminals or puncturing insulation. Read this! Quote Link to comment Share on other sites More sharing options...
GregKneupper Posted June 12, 2010 Share Posted June 12, 2010 I have replaced many under valve cover harnesses on the 6.4 for misfires and injector circuit fault codes. You can wiggle on the connector at the injector and the miss will dissapear. Quote Link to comment Share on other sites More sharing options...
clint80 Posted June 12, 2010 Share Posted June 12, 2010 +1 i replaced a couple under valve cover harnesses as well for that code. while performing ford's ppt the truck is off, giving you good readings, and it may only create a loose connection while its running. I did have one though with an int. miss, ended up being main engine harness rubbing on the fuel line like the ssm 20471. Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted June 12, 2010 Share Posted June 12, 2010 I have replaced many under valve cover harnesses on the 6.4 for misfires and injector circuit fault codes. You can wiggle on the connector at the injector and the miss will dissapear. Good to know! I havent come across this yet but I will keep this in mind... or try to. Quote Link to comment Share on other sites More sharing options...
joshbuys Posted June 12, 2010 Share Posted June 12, 2010 I haven't had to replace one for a misfire, but I did have one that had high resistance on the FRP sensor circuit causing a lack of power. Set a code for High FRP....don't remember the code - maybe a P0089 or something like that Quote Link to comment Share on other sites More sharing options...
robp823 Posted June 14, 2010 Author Share Posted June 14, 2010 Thanks for all the help guys.Just to let you know a uvc harness fixed it.After everything ohmed out good. Quote Link to comment Share on other sites More sharing options...
Jonathan302 Posted June 20, 2010 Share Posted June 20, 2010 I have replaced many under valve cover harnesses on the 6.4 for misfires and injector circuit fault codes. You can wiggle on the connector at the injector and the miss will dissapear. +2 here Just got one this week with this concern. Quote Link to comment Share on other sites More sharing options...
duff Posted January 27, 2011 Share Posted January 27, 2011 have f450 p0308 - missfire cyl. 8 - cycle key off restart runs fine until engine load then starts missfire until key cycle - injector was replaced - wire harness test fine Quote Link to comment Share on other sites More sharing options...
Mikill Posted January 28, 2011 Share Posted January 28, 2011 When it comes to the electrical codes on the 6.4 I always check all the wiring and plug in a test injector before replacing anything. I have had a few that UVC harness fixed the concern. I have had some that injectors fixed the concern and I have had one that the PCM fixed the concern. Quote Link to comment Share on other sites More sharing options...
deezul Posted January 28, 2011 Share Posted January 28, 2011 I haven't really had much to do with the 6.4's yet (after the six liter our dealership hasn't really been able to move many diesels) but it sounds like the UVC harness is very problematic, good thing to remember for the future. More times then not it's the harness not the injector (electrically?)? Quote Link to comment Share on other sites More sharing options...
Mikill Posted January 29, 2011 Share Posted January 29, 2011 I haven't really had much to do with the 6.4's yet (after the six liter our dealership hasn't really been able to move many diesels) but it sounds like the UVC harness is very problematic, good thing to remember for the future. More times then not it's the harness not the injector (electrically?)? Actually I believe I have had about an equal amount of injectors fix electrical concerns as I have UVC harness. Quote Link to comment Share on other sites More sharing options...
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