We just finished rebuilding the top end, 2003 F-350 crew, 4x4: head gasket, ARP studs, upgraded EGR. Truck runs fine and starts when block heater gets it warm.

PROBLEM: the dash glow plug light comes on and almost immediately goes out and the glow plugs are not heating. (we try this with the engine cold) Checked all plugs and everything seems to be plugged in O.K.

?????? Will a high-end Snap On diagnostic tool be able to figure this out? Any thoughts on the problem??

 

Probably a bad relay or maybe crossed wires on the relay when you put it back together

 

I have posted the test specs for the glow plugs and relays on here before, I can't recall them off of the top of my head and I have the info at work. I can get it on Wednesday, or try doing a search on here using my username and glow plugs. I'll see if I can find it too. You basically test each glow plug to ground, measuring resistance, then do the same for the glow plug control module. Also it's worth noting the glow plug on time, is actually independent of the wait to start light. When the light goes out, it doesn't mean the glow plugs are out... the glow plugs are on for a determined amount of time by the PCM based on oil temp and elevation. They can be on for a max of 120 seconds, but never more. If oil temp is over (I believe, 131*) they don't come on at all. How are you determining the glow plugs are not on? A hard cold start doesn't always mean glow plugs...

 

Hi, Mike.
I was pretty sure it was glow plugs because with the block heater, it always fired right up. On checking the wiring, found the 2 smaller auxiliary + wires that bolt on the main battery terminal had worked loose. Once I tightened them down, everything returned to normal. I am constantly amazed at how much these engines depend on all of the electrical stuff being just right.
Thanks for all of the info. I'm sure that it will be used someday when a real glow plug problem rears its head.
On a bone cold engine, can I assume the glow plugs will burn for 120 secs?
Great looking truck of yours. Nice stacks.
Lawrence:yeah :

 

Here is a link to one write up on testing for future use

https://www.dieselbombers.com/94-98-...tml#post403396

 

The easiest way to see how long they're on for... park facing a garage door, turn your headlights on, and turn the key forward. When the headlights get brighter all of a sudden, it's because the glow plugs just went out. Kind of a redneck way to see how long they're on for. Either way, the point is to know that they're independent of the light on your dash, for whatever reason.

Typically when I do bone cold starts, I really don't even pay attention to the light or glow plugs. I turn the key and listen for the injectors buzzing. I let them run their completely cycle of buzzing, turn the key off, then cycle one more time. When they stop, I start the truck.