Hello all!

Running into an issue with the X that I can not seem to track down.

A while back I was having some running and starting issues, with no SEL. After days of research and a gameplan, I bought a BT OBD reader and downloaded Forscan only to find a whole mess of codes. Everything pointed to glow pug/injector system wiring, and after testing the valve cover connectors I found the problem.
Driver's side UVC wiring was replaced at some point with the newer style, but wiring was roasted and shorting out inside. Passenger side was original but same problem. Replaced both along with one glow plug that didn't ohm out, double checked the wiring harness that goes over the driver's side valve cover for wear, and put it all back together. This cleared almost all codes, and no more issues starting or running.

Only code that remained was a P0683-C and a SEL when my Hydra chip was installed, and a P0683-P and no SEL w/out the hydra. Terrible fuel economy as well, and still a bit of white smoke at startup but nothing crazy. No issues running with the hydra and php tunes installed (other than fuel economy) so it seemed to be OK but I could not live with that last code.

I pulled the connectors at the GPCM to find a few terminals roasted as well on both the GPCM side and wiring harness side (both connectors but more so on the black one vs the green one). The most melted terminals were the main positive ones coming from the starter relay fusible links, and I believe what caused this was the shorts under the valve covers.

I replaced both the GPCM (aftermarket not motorcraft) and the harnesses with no change. It still throws a P0683-C with the Hydra and a -P without (most of the time, sometimes -C as well). It will also throw those codes with the new wiring harnesses and the old GPCM plugged in, and with no GPCM plugged in at all.

Before I spring for the Motorcraft GPCM I think I still need to make sure there are no more shorted wires or fuses somewhere North of those GPCM harnesses since everything from the glow plugs to the harnesses has been replaced (hopefully it didn't make it all the way to the PCM).

My thoughts to move forward are the following:

1. Verify that the Green GPCM connector comm wire is good all the way to the PCM, but wanted to verify the color of this wire as well as the pin on the PCM connector to be #8 as stated online. It seems there is more info on the GPCM for 6.0l vs the 7.3l Ex and Cali trucks, and I doubt the 6.0 and 7.3 wiring is the exact same.
2. Test + power at the GPCM harnesses with KOEO, but I assume they are since it is started when cold (under 40 degrees).
3. Check all of the fuses relating to the glow plug system, pcm and no start issues.
4. Check grounds

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My questions to the forum are:

1. In regards to fuses to check, what is the full list of fuses and locations that could have been affected by the glow plug system and injector system wiring short, and how do I properly check them (I have seen in more than one forum that even if a fuse looks to be intact replace it anyway)?
2. For wiring and connectors to check, where is the fusible link that provides power from the driver's side battery to the GPCM connectors? Is the Comm wire that goes from the GPCM to the PCM wht/green, is it located at PCM pin 8, and is that on the PCM connector in the cab or in the wheel well that I would be checking for ohm 1-2ohm? 42pin connector?
3. I have read that every sensor involved in the 7.3 running has a comm wire connected to the PCM to communicate that everything is normal and reads a constant 5ish volts. Is that correct and should I check for that as well? Any other sensors I can easily rule out while I am at it (MAP, IPR, HPOP, CPS, ICP, TPS, OIL Temp, IDM, etc)?
4. Should I pull the PCM out and check for any shorts or burns on it? Easy way to bench test the PCM at home? I do not have a breakout box for testing procedures I have seen.

Any other thoughts, advice, and clarification in regards to testing the PCM pins would be much appreciated. Most of what I have read as far as which pins and which connectors have left me confused as there are multiple main wiring harness and PCM connectors, and the threads are old and dead. Figured I would start a fresh one with some fresh advice!


To recap in short (pun intended):
Under valve cover wiring shorted out which shorted out the old GPCM (most likely, not sure how to bench test it but I still have it if possible) and definitely melted the old GPCM wire harnesses. Replaced the under valve cover wiring and one GP that needed to be swapped (also tested all injectors), pigtails to the UVC wiring, and the GPCM + GPCM wiring pigtails (non motorcraft). All codes are cleared except the P0683-C and there is still a SEL and poor fuel economy (under 10 citiy, 12hwy. I was getting 17 and 20+ before). It will cold start after one WTS iteration and a few cranks with a little white smoke.

 

Ref: fuel economy.

I religiously record every drop of fuel in my vehicles, using an app on my phone.

I can look back and am unable to determine that adding the Hydra had any effect at all.
I keep notes on each tank, as to terrain, towing? etc.

my right foot seems to have more effect than anything else...
if towing, I can go slower, let the CC do the job, and it does a better job, over very long trips, like 1500 miles in one trip.

I have seen down to 9 mpg, and as high as 17 mpg, depends on what I am doing and where?

 

I hear you and I agree. I have done multiple 8hr+ road trips in the X over the years and have gotten 800-900 miles on one 44g tank running at 75-80 mph at its best. The best would have been a round 21mpg with only 2 stops in 900 miles in a 15hr period. The greatest affects on fuel economy for me has been the tune and stop and go of any kind, or if something engine-wise has been sending bad feedback to the PCM.

Jelibuilt had a killer fuel economy tune I used to run would show about 21mpg on the overhead screen and thats what I would get when tracking fillups and mileage, but the shifting was funky and hard. Php tunes in the X have been smooth with good power but best ever I've seen is 17-18mpg.

Back to the problem at hand, when the rough running/starting began awhile back the fuel economy dropped. I recall replacing some other sensors in the past that would immediately return the fuel economy to normal (CPS, IPR, fixing a stuck open EBPV), and I would gladly go after one of those again if there was any sign of familiar symptoms. However, there is not and the only code it keeps running that sets off the SEL is P0683-C. I would really like to track this down and return the glow plug system to normal before looking more into fuel economy. That is really secondary at this moment.

The fact that it shows that code with the new GPCM plugged in, the old one plugged in, or no GPCM plugged in tells me there is either a communication error between the GPCM and the PCM, or the new one is a cheap dud. I just want to make sure I rule the rest of the system and anything else that could have shorted between it and the PCM itself out before springing for the simplest fix which would be a Motorcraft replacement.

 

your Excursion must be 2wd, mine is 4wd and weighs 8000 on the scales with fuel, nothing else in it.

 

It is 4x4. I would say about 7500-8000lbs full of fuel sounds about right.I have tracked my fuel consumption in all of the daily and eco tunes from Jeli and PHP front hubs not locked. What I stated is accurate, and as far as I've seen the overhead display in comparison to actual fuel tracking is pretty close. Proper tunes are 100% the best way to better fuel economy, only second to not driving like an *******. The overhead display is more useful as a dummy guage to remember to let off the pedal, or on very long road trips where your speed isn't changing.Regardless, I'm not really looking for fuel economy advice.

I went from 15-17 city and 20+hwy before with no wiring/sensor problems, to 8-10 city and 12hwy with the current status.


Back to my problem. Anyone with an Excursion or Cali truck run into a fried GPCM? Any help on my questions is much appreciated.

 

A few suggestions:

1) It wasn't clear to me from your first post, but are you confident the green and black connectors to the GPCM are in good shape now?
2) If so, check the harnesses back from them as best you can. I know it's a pain, but the fact the your old GPCM, and new 3rd party GPCM and no GPCM all behave the same way points back to something before the module, IMHO.

To answer your last question directly, yes, I did have a GPCM go bad a number of years ago, and documented what I found here. (Search for threads started by me in this forum to find it.) IIRC, the symptom was an entire bank of glow plugs throwing codes at once. Different than what you are seeing.

I don't need to tell you this, but will, anyway: Motorcraft>non for any sensor or piece of electronics on these things. RiffRaff is your friend.

No help on the mileage, but I agree with your approach. Let's fix what you know is broke, then proceed to the unknown stuff.

Mark

 

1) Yes, the new connectors are solid. I double checked them the other day to ensure they were tight and didn't have any loose terminals. When pulling on all individual wires I found one of the glow plug ones on the green connector pulled right out. I was able to pop it back in.
2) Roger. I think I will test the wires one by one for continuity from connector to connector and check them off the list. So GPCM to 42pin I think, then 42pin to the drivers side wheel well connector, and then the PCM. Hopefully I can trace it down and report my findings.

Good deal, I will take a look at your old thread. I did have the entire drivers side bank throwing codes, but it was most likely a combo of the GPCM and the wiring in the valve cover itself.

Agreed, might check my local parts store for Motorcraft and just pop it in. If it fixes it I could always return it and head to RiffRaff for a solid price.

Thanks Mark.

 

Agreed, might check my local parts store for Motorcraft and just pop it in. If it fixes it I could always return it and head to RiffRaff for a solid price.

Thanks Mark


when you say parts store do you mean ford or international? if not i would not trust them anymore than fleabay/scamazon

 

For the poor fuel economy...what's the condition of the up-pipes and CAC boots below the spider at the connection to the intake manifolds? This was most of my issue and it got so bad it would bellow black smoke when in the throttle hard. For the rough running hard start...have you unplugged the ICP to see if that corrects it or looked to see if there's oil in the connection? The CPS and IPR would also be suspect in the aforementioned, but I'd also look at fuel pressure. I had a similar issue that turned out to be the ICP, but I had no oil in the connector...just a bad ICP. I also had problems with the GPCM relative to melted main terminals. The black side shares power with the AIH, which caused part of my problem here https://www.ford-trucks.com/forums/1...to-test-2.html in post #26. I would also look at this post relative to the internal pins needing to get tightened back up https://www.ford-trucks.com/forums/1...and-8-a-2.html given you pulled one out. Like I mentioned in the first link, I would rather buy a used known good GPCM out of an Excursion, Cali vehicle, 6.0L, or 6.4L over any aftermarket junk. This is what I did in fact and instead of splicing the wires I re-pinned the connectors several years ago. The SES light came on several months back for the glow plugs and I need to look back into it, but being in south Texas it's not a priority...especially since the Excursion stays in the garage right next to the water heater.

 

Here's a wiring diagram to help pinout the GPCM. For 2002 but hopefully same.