I'll try to keep this short while still getting all the details in. Just bought this truck, 04 6.0. Came out from work one morning and it would not start. Temp was about 10 degrees. Ended up killing the batts trying to get it going. Had to tow it home. The next day, I decided to get new batteries and test the FICM. Well key on it was about 19v during buzz test, then would jump up to 48v. Cranking it would drop back down to 19v and the truck would never start. Attempted the re-solder repair and no dice, and it was easy to see that it had been repaired at least once before I got to it. Found a local shop that specializes in powerstrokes and does FICM rebuilds. However, he said he could NOT rebuild my 7 pin FICM and would have to give me a 4 pin instead. I was skeptical at hearing that, but was in a pinch and needed my truck so I bought the rebuilt 4 pin. Installed it and the truck fired right up, now mind you, it had been plugged in all night. I buttoned up the truck assuming all was well now, and went on to work. Truck sat overnight unplugged and when I came out in the morning to start it, it would not start. Just when I was about to give up all hope, and the new batts were beginning to tire out, the truck finally started, but idled rough for a few minutes with some decent white smoke....I'm assuming some stiction issues. But after a minute or so, it cleared up and ran normal. I have not tested the new FICM yet, and now have a code P0673, cylinder #3 glow plug circuit. Now I'm assuming if one plug is bad, it would not hinder the truck starting that much.....Possible I fried the GPCM amongst all the recent cranking attempts and wiping out one set of batteries?? Is there any definitive way to test the GPCM, I've read some posts saying you can and some saying you can't. Can I just probe each individual wire coming from the gpcm to see if power is being supplied back to the glow plugs? I will test the rebuilt FICM I got this weekend to be sure it's not the culprit, but does this sound like anything else besides glow plugs maybe? Truck doesn't seem to have any other issues and runs great after warm up. Unfortunately I don't have any type of scanner or monitor yet to give numbers and whatnot. The code I did have pulled was done at the local parts store.

 

You would get a code for the GPCM if it was fried. You either have a bad #3 glow plug or a bad circuit. They can both be tested with a DVOM. I would also retest the FICM. Did you also have your charging system tested when the new batteries were installed?

FYI: The glow plugs stay on for about 2 minutes AFTER the wait to start light goes out. It might benefit you to wait for 30 or 40 seconds after key on to try and start your truck.

 

The reason I lean towards GPCM being bad, is because the 1 major thread I found about testing it, the guy (presumably a mechanic) says he has seen his fair share of trucks come in with codes flagging just one or more specific cylinders for glow plugs being bad, and it ended up being the GPCM instead. So I will definitely test it with a DVOM and also the FICM too. I did not have the charging system tested when I put the new batteries in. What would I be looking for in that case, as the batteries are without a doubt being charged when I drive and I even put a DVOM on just yesterday while it was high idling and got 14.4v at both batts.

And yes, I did know the glow plugs stay on for up to 2 minutes depending on EOT at the time. But that being said, they are still on whilst cranking, so would it make much of a difference to wait longer after the light goes off?? Maybe that's just my brain not comprehending the difference lol. Thank you for the response though, I will definitely check what you suggested so far.

 

Waiting after the light goes out lets the internal cylinder temp get warmer thus allowing the fuel to combust easier, especially in really cold temps. If your alt. is out putting 14.4V I'd think it's OK.

I'd like to hear a tech weigh in on the GPCM, but if it's faulty the PCM should throw a code and possibly a CEL because it's an emissions item.

 

hope you get it going

 

Cranking rpm must be at least 150rpm. Also you must have 500psi in oil pressure at ICP prior to firing. A lot of guys including my self install a starter from a 6.4... cranking rpms are like night and day.... a cheap bluetooth device and forscan app on an android device work well... or scan guage ll. Ok for monitoring but not really pulling codes. Forscan pulls codes and monitors really well.

 

 

Ha yeah that's what I get for staying up late ... lol