I have read many of the questions and responses to diesel cold starting problems over the last few days. My Excursion will not start in the cold. If I plug it in for a bit, it starts perfectly. I have changed the Glow Plug relay but I still get no output voltage (from the 2nd large post on the solenoid). There is 12.2 coming in though.

Next to the relay/solenoid switch, there is a 2" x 3" ribbed aluminum unit that has 2 connectors going in/out. I am wondering, on the Excursions, does that have something to do w/ activating the solenoid that triggers the glow plugs. Lastly, is there a simple way of testing the glow plugs. It appears they are located under the valve covers (which initially seems a hastle to remove). Is there any easy way I can activate the glow plugs just to test if the truck will start? Thanks, Ray

 

Sounds like you have a GPCM with that ribbed alluminum box. That Relay you tested sounds like the IAH relay. sometime in 2000 Ford switched to the GPCM from a Relay for the glow plugs in the X's and California trucks.

 

The lightbulb has just gone off! Alan, thanks. As I mentioned, I have read a ton of posts and just couldn't get it. Had I fully grasped Ryan Arthur's responses, I might have picked that up w/o bothering you. After looking carefully at one of the links that discussed IAH's, I saw that some 7.3L have two solenoids and some have a solenoid and a relay. I should have know something was strange when the HDC908 I purchased didn't fit and was undersized. But for 40 bucks, it sounded like a deal. I ordered the relay (the aluminum ribbed piece) and its being delivered to the shop tonight. The truck has been in 15 degree weather - outside all day, so this will be a good test. Bottom line is that I am starting to understand this a bit better. BTW, what does the IAH do on the Excursion?

 

As little as it does on the F trucks. If the truck is at idle after starting and glowplugs are off and you havent touched the brake or accelerator and it is below 32*F it will come on to warm the intake air. It only occurs once per key on event so if you crank and drive off it will not come on later if you go back to idle.

 

is there a way to test to make sure that the glow plugs are working. the wait to start light comes on as it should, does this not come on when they are not working, or does it always come on anyways

 

Alan, changing the relay worked perfectly. A bit more expensive than the solenoid, but getting the truck to start was well worth it.

An unusual thing seems to be occuring and I'm wondering if my repair has anything to do with it. For some reason, regardless of whether I put the AC or heater on, the air will only flow out of the defroster vents. Nothing I do seems to be change it. I looked at all the connections that I might have touched when I replaced the relay, but can't find anything out of order. This might just be a coincidence, but any idea what causes this misdirection?

 

Ray,

I had the same set of problems with my F250. The dealer replaced a component they called the "clock spring" which fixed the vents. The default position for the vents if they break is on the defrost setting.

Tom

 

Tom, do you know where the "clock spring" is located on the Excursion. Maybe I can replace this myself. Must have been just a coincidence that when I changed the relay, the vents didn't work. Very weird. Let me know.... Thanks, Ray

 

A vacuum leak can also cause a default to the defrost vents. The clockspring is under the steering at the top of the column

 

if your excursion is 4 wheel drive and it has electronic shift on the fly, see if the hubs engage. That will tell you if you've got a vacuum leak. I've never heard of a clockspring causing one to default to defrost. How does it cause that? My clockspring is in need of replacement right now and my A/C and heat work normally.

 

This has taken a long time to diagnose. I cannot say these results will be the same on anything by a Ford Excursion 7.3. Here goes: I traced ALL the vaccum lines going under the dash. No breaks. Nothing leaking under the hood either. BUT, there is a vacuum pump (located on the inner fender well - right where the fender mounts on the passenger side) it looks like a little fish pump and it creates vacuum to the reservoir. That unit had no suction and was constantly on. I replaced that. Its part number is 6c3z-2a451-a. Since the dealer had it in stock, I assumed it was a part that failed often. My concern was what made it fail in the first place. After replacing the unit, the new one ran but could never create enough vacuum in the reservoir. I suspected that (for some reason). Coming out of the reservoir (located on the fender well too) are two vacuum hoses. One operates the heater assembly, the other goes to a valve which controls the 4 wheel drive. When in 2WD, this unit is in the off position. The diaphram should hold vacuum; in my case it didn't and therefore forced the pump to continiously be on. The Ford number for this valve is 6c3z-9h465-ba. Once I installed that, the pump created vacuum and the reservoir held pressue. That enabled the heater and AC controls to work properly. The bad news is that once I enable 4WD, the reservoir depletes and the heater controls don't work and go back to defrost. Since there is only one line to the 4wd from this valve, I will trace where the break is tonight.

Any suggestions on the most obvious place for a break would be helpful.