Ok, so yes, I did search the forums, extensively. But i'm getting mixed signals and I think I might have a different issue or maybe a couple of them.

The truck runs beautifully once it's started. I just got this truck last week but my first tank of in-town driving got me 15+ mpg. She seems really healthy other than this problem.

The Problem:

The truck gives me a healthy crank but no start issue basically every time it's below 45 degrees. It cranks nicely, the WTS light comes on and the tach moves. The tailpipe bellows tons of white smoke while cranking. Every time I plug the truck in for at least an hour it starts perfectly, it has never given me an issue after it's been plugged in. Also, the oil level is full.

So you're thinking, classic glow plug issue, right?

Well, two days ago the truck had been sitting all morning unplugged. It was unplugged because it was 75 degrees and I went to start it at 2pm so it was nice and warm. The truck gave me the same issue again just like if it was cold outside.

I had ordered a CPS and it came in the mail so I changed that out (Motorcraft of course) and that didn't fix it, still no start, everything the same. Out of curiosity I grabbed my wife's hair dryer and stuck it in the intake tube. I gave it about 15 seconds and tried the key. The truck started more effortlessly than ever before.

I'm really lost on this one, any ideas?

I just grabbed my multimeter and did some poking around;

Both batteries 12.6v (seems less than ideal but it sure sounds strong while cranking)
Hot side of GPR 12.55v
Keyed side of GPR 0 while off
Keyed side of GPR while on 12.05v

What's really confusing is that i've seen it start great at 50 degrees unplugged and then fail to start at 75 degrees just 2-3 days later. I can't think that not starting at 75 degrees has anything to do with the glow plug system, right?

Whats the next step?

 

You already answered it.

Gp relay 12.55 before...12.05 after... That's half a volt drop across the solenoid.Replace it!! Get a stancor. Yes it should start otherwise without gp but that relay is bad.
Also check system voltage cranking.you HAVE to maintain at a minimum 10.5v or the idm can not function. Check gps them selves and valve cover connections for burnt pins.

Go from there and see how she starts.

 

You need to measure the HOT side of the relay with the key ON. It's the difference between THAT and the keyed side that counts. Actually, the keyed side voltage seems too high. If you have good working GPs, they should draw the key-on voltage to about 11.5. I'm guessing you have one or more failed GPs, or bad wiring to them, so less GP draw than expected. And as said, measure the resistance of the GPs themselves, through the UVCH connectors.

 

This morning - Cranking voltage goes between high 10's and low 11's. Never getting below 10.5v.

With key on this morning - Hot side is 12.09v - keyed on side is 12.07v

I started it an hour ago just to make sure it was going to start, it started right up (47 degrees). I just went out to leave for the day and now it won't start again. This is frustrating

 

Maybe your IPR is sticking?

 

That suggests the relay is good (difference is less than 0.3V.

Have you checked the GPs (resistance) yet?

At the times it doesn't start, have you tried leaving the key in RUN, to run the glow plugs longer, say, an extra 10-15 seconds?

 

I haven't checked the plugs themselves yet but I'm pretty convinced that since it did the same thing at 75° this is something other than the gp system.

This morning I did try leaving the key forward for longer and it didn't help. The good old hair drier didn't help either.

The other clue is that at no time does it start hard or act cold. It either starts right up and sounds great or it cranks and doesn't start at all. It's not like I crank it for ten seconds and it finally starts, if it's going to start it does it immediately.

I put another quart of oil in it this morning just to make sure that sensor is happy. So far it's started great about six times for me today, but it's warm outside...

 

75F is still a COLD engine, compared to the temperatures at which diesel combusts, and the temperatures at which the GPs run. A hair dryer won't generate enough heat to make a difference. The block heater _might_. 'Course, you may have multiple problems. What sensor are you referring to?

 

I made some time today and checked the resistance on the glow plugs at the connectors on the valve cover gaskets. Here's what I found as looking from the front of the engine;

Back Pass.
- Open Loop
- 9.53

Back Driv.
- Open Loop
- Open Loop


Front Pass.
- 357.1
- 1.4

Front Driv.
- 1.8
- 1.2

That doesn't look good now does it?

 

Looks like you have three good glow plugs. That whould explain why your voltage isn't that low with key on (much less draw than normal), and would def. explain the starting issues. The three good ones are kind of meaningless, except for diagnostic/informational purposes. If you're pulling the covers, may as well replace all eight. Motorcraft/Beru ZD-11 ONLY.

 

Well, that was a lot less fun than I was hoping it would be. I pulled the Passenger's side cover and installed four brand spanking new Motorcraft plugs. Those two bolts, the rear one by the firewall and the one next to it by the heater box are half the job. The old plugs came right out for me. I had heard horror stories about breaking one off in the head but none of mine were anything like that.

After I finished up it was 36* outside and it started right up. We'll see how it goes in the morning. Theoretically I now have 6 working plugs. But that's assuming all the new ones work out of the box. Speaking of which;

What exactly does a "2yr limited warranty" mean on Motorcraft glow plugs? And how long do they usually last?

 

Mine lasted 17 years. The only reason I replaced them is because I had everything apart replacing the valve cover gaskets and pigtails.

 

Well, those new glow plugs fixed it right up. It's started fine everytime since I replaced them. Two days ago I had to scrape snow off the windshield off and she still started without any complaints. Thanks guys!