I have a 1995 7.3L DI with 355k miles, and recently it didn't want to start on a cooler morning (upper 40's). I tried 6 times with it just cranking, then switched cars and went hunting. When I came back early afternoon with temps in the upper 70's, it started immediately, and continued to start fine the rest of the day. But it also started again the next morning, which was cool again in the upper 40's.
So I started going through the flow chart and figured it must be related to the glow plug system.
The GPR showed power at both posts. I later measuered this and the voltage drop is 0.85V across them. I saw elsewhere that anything over 0.5V isn't great.
I checked resistance on all the glow plugs, and they were in the 0.6-0.9 Ohm range, with the exception of #1. I could not get any reading on #1, so yesterday I replaced the entire passenger side bank of glow plugs.

So the truck starts, but I can't convince myself that one bad plug out of 8 and a GPR that is only slightly higher voltage drop than it shoud be is enough to explain a no start at ~47 degrees after 6 attempts? I leave in 12 days for a deer hunt in WY, where I'll be 4000 feet higher in elevation, and a most likely 10-20 degrees colder. I don't want my truck to fail on a deer hunt I have waited over 10 years to draw.

I purchased a back up Cam Position Sensor. When those start to fail, is it ever intermittent? In the past I have only had them fail while driving, but I do seem to recall once that it worked again for a while after the first time it stopped running.

Should I replace a GPR that is reporting a 0.85V drop across the posts as further insurance? At least that's a lot easier to change out than the dang glow plugs themselves...

I know it isn't related to oil levels or the High Pressure Oil Pump. I had just changed the oil, the levels are good, and I replaced the HPOP just a couple years ago.

Any other suggestions that would make me feel more confident in my rig heading off to my WY hunt?

 

I'd change the other plugs and have a gpr in the glove box just in case.

Are you plugging it in at night?

 

At 355K, that is a lot of miles if the injectors are original. My brother has a 2000 F350 that had about that kind of mileage on the injectors, and it got so it wouldn't start first time without being plugged in when the temps reached 40 degrees. The fix on his truck was a set of injectors. I think they were just so worn that they didn't have the correct spray pattern, probably just injecting the fuel. Just as a check, the next time it doesn't start try jumping the 2 large terminals on the GP rely with a screw driver for approx. 30 seconds then try to start. If it fires up the relay is bad. Sometimes the internal contacts get burned in one spot and the relay does not make connection. Then on the next try the internal disc moves off the burned spot and the relay works.

 

Edgethis - I haven't been plugging in, because that won't be an option when I'm out in the field.
Farmert - I hadn't considered injectors, that's something worth investigating.

Bringing a spare GPR is starting to sound like a good idea. I've read that it should be 0.5V max drop across the posts, when engaged, and mine read 0.85V. So maybe it is starting to fail.

Harley

 

Just had a no start because of a gpr. It would crank and crank and pour out white smoke. Popped a new one in and she was good to go