Starts right up if it's plugged in. Might have some time this weekend to work on the GP relay to make sure it's working. My meter is a good one, self ranging Fluke787 (I work in the electrical controls industry), so no problem there. Since the people that had it before me replaced the GP relay, and it still looks new, I'm guessing there's likely a problem with all of the GP's or a wiring harness issue. Here's the kicker, shortly after I bought the truck, I found out it was a repo that had a bad tranny and sat for over 6yrs without running. The tranny went bad in 2006, it was repo'ed in 2007, and the report shows the mechanical issue sometime in 2006, probably the reason it go repo'ed. Anyway, then shifted from several (3+) auction yards, but no mileage added to the odometer. Then finally one of the dealers rebuilt the tranny this winter, put about 400miles on it, and sold it to me! There's a sucker born every minute. I would think the truck was pretty well taken care of, as the paint job is still like brand new without a scratch on it, not even sun faded. Anyway, it's been quite a lesson in diesel troubleshooting for me in the last 4 months! Thanks again for you help.

 

Just a follow-up... I did replace the GP's and all was well. Then, about a month later I noticed diesel on top of the coolant in the overflow tank. Ended up replacing all of the injector cups with a tool I purchased off of ebay. It went pretty well, and so far, other than 4x4 problems with it not going into 4wd, the truck has performed flawlessly. Anyone got any ideas on what could be going on with the ESOF 4wd? I've replace the transfer case shift motor, the control module (used) and swapped out relays to prove the relay is good. Checked the switch, but it acts flaky. It has the correct ohm drops across each resistor in the switch, but I would think it wouldn't pull down the voltage upstream of the resistors? Without the switch plugged in, the power wire has 12vdc on it, but when I plug it in, it drops to about 4vdc? I can understand that on the 'switch-side' of the resistors it should be a different voltage, cut can't understand why the supply side would drop? Still a bad control module? Anyway, sorry it took me a year to get back on here with an update...

 

May be reading the reference voltage?

KOEO, Do the 4x4 relays click when High/Low ranges are selected? After the range switch is cycled, the system with try to engage the relays/gearmotor 5 times within 20 seconds.. Try the selections in neutral/brake applied?

 

The fix was easy, but a pain to come by. Took the entire 4wd selector switch out, and pulled it apart. Noticed that the contacts that rotate/slide as the switch is turned, seemed to be making connection, but very hard to tell. So I put a little bit of a 'field' bend in them just to make sure they were touching and 'contacting' the switch contacts enough to keep the connection to the 4wd module. Anyway, that fixed it. They are a copper 'spider' looking contacts, with 3 points on them, and slightly bent to make the contact pressure, like a pre-loaded spring. But, these seemed weak, so I 're-bent' them every so slightly, and it hasn't missed a beat yet. Been driving it for 3 months off and on with 4wd and it works great! Thanks for the help everyone!

 

Glad you got it figured out.