Really at my wits end here. I have a 2003 excursion 7.3 L, that will not start when the engine is cold unless I have the block heater plugged in. Where the wait to start light stays on for three or four seconds then starts no problem. If it sits overnight not plugged in for 6 to 12 hours (depending on how cold it is outside, but even as "warm" as 10 Celsius) the WTS light stays on for 8-9 seconds and then will crank but no start. It blows lots of blue white smoke at this point. Also if it sits for 3-4 hours without running at these temps, when it starts it runs really rough for the first 5-10 minutes of driving, then smooths out.
I have changed out the glow plugs, the glow plug relay, the air heater relay, 2 brand new batteries... All to no avail.
The fact that it starts fine when plugged in made me wonder if maybe I should try swapping out the fuel bowl heater? Maybe the fuel just needs that little bit extra warmth before it hits the plugs? I'm no mechanic tho.
I know there's lots of no cold start threads here and in other forums, I've read hundreds but none have helped so far, so I'm sorry if anyone thinks this topic has been beat to death. Just hoping someone will read my issues and have new insight.
Any help would be appreciated!

 

How many miles on your truck? Sounds like tired injectors.

 

Your Excursion shouldn't have a GPR you probably have a GPCM Glow Plug Control Module.

Take a look at my Glow Plug Page for some insight

The Fuel Heater and AIH are not your problem.

 

Truck has about 340,000 kms on it, which I believe woks out to around 214k miles... Was really hoping it wasn't injectors, they're awful pricey.
woodnthings, from looking at the diagram on your page, I'd guess you're right, I have the GPCM... Rectangular silver piece, about 4" long? It was another pricey part. I just want the dang thing to run lol

 

Check out my GPCM troubleshooting manual upload

 

i missed that it was on an ex

 

Try switching to synthetic oil. This will help smooth out the romps and rough idle on a cold engine. I think you have something else going with the glow plug system if it won't start at all.

 

That's very handy! Thanks woodnthings! I'll have a go thru it tomorow, too dark out right now.
It's also probably worth mentioning that it's not throwing any codes. It had been before I changed the glow plugs, a comm error between plugs and pcm I believe, but cleared up after changing them out.
Is there a (relatively) easy way to check my injectors?

 

I am running Rotella T6 synthetic 5w-40 right now, still pretty rough unfortunately... But thanks

 

Have you ohmed out the glow plugs through the connector on the valve cover gasket? I applaud your efforts to have everything 100%, but it's the connections between everything that commonly fails. It might also help to click the UVCH link in my signature, and there are other very useful links for hard/no starts.

Your injectors are about due - and this winter isn't going to make things better.

 

My vote is injectors. Sounds very familiar. I recommend reading my old threads back a few years ago. Glow plugs would be a place to start. Fairly easy to check and won't cost anything to ohm out. Relay as well.look at date 10-22-2011. Good luck. Scott

 

+1 for injectors,if you are bored and wantto read an (part of) my no start cold start injector saga, click on my cold start link in my signature.