well, i've tried both IDMs i have and they both do the same thing - and were both working fine previously. what i haven't done is to give the IDM its own power and ground separate from the PCM. i'm leary to do something like that though.

plus, the low voltage at the glove box light happens with the key off as well as on, so figuring this plays some role in the problem, i'm going to hunt this down before doing anything drastic with those expensive aluminum boxes :-)

 

I know the IDM has a ground wire in the harness, but it also bolts directly to the fender. Is there a chance the case of the IDM itself needs to be grounded?

It really sounds like you have a voltage draw issue there somewhere pulling your system voltage down. When that happens, the easiest thing to do is to disconnect just about everything that is non-essential (Pull a bunch of maxifuses) and then add them back one by one until the issue shows up again.

One more thought is that, IIRC you went to the SD UVCWH, correct? Have you disconnected those at the valve covers to make sure you don't have a wire crossed somewhere in that process that is going to ground through either the GP's or Injectors?

If that isn't a concern, I would pull all the Maxi Fuses except for anything having to do with engine control (PCM, IDM, etc) then turn the key and see if you get the same chattering. If you don't, then replace the fuses one at a time and retest each time until you get the same deal.

You didn't replace the GPR while you were doing this did you? That's one more thing you could disconnect as a test.

 

That's a good approach Nate. I should have thought of that!

In the extreme cause I could kill everything and just give power to the pcm and Idm through the fuse box. I've been keeping the dash alive knowing that so much of the pcm's circuitry goes through there but it can't get any worse to kill those circuits. It couldnt not start any worse :-)

I did ground the Idm box itself though and it didn't change anything.

And both power wires (coil and contactor) are off the gpr right now.

and i did unplug the SD valve cover harnesses. and checked all the pins back to the IDM for continuity where it should be and no-continuity to other pins/GP wires (to make sure there were not shorts). not that there definitely aren't problems there, but i don't the injectors have ever tried to fire yet, so problems wouldnt have reared their head yet!

 

I think that once you find the added resistance to the glove box light, that you'll find out why your voltage is dropping on cranking.

 

i sure hope so!

 

I was looking through your rebuild/paint thread and noticed in those pics that the ground from the back of the passenger side head to the cab wasn't there. Or at least from my phone I couldn't see it. It looks like a pretty significant ground wire might not have anything to do with your situation. I just thought I would mention it.

 

interesting. i don't believe either of my trucks had a ground strap from the head to anywhere. they are 96 and 97 trucks. any chance its a difference between years?

or maybe the PO's on my trucks did away with them?

in any case, since those pictures were taken, i have added the two main ground cables back to the engine that were on it when i took it apart - one on either side of the crank on the front of the engine. it killed me to grind the nice new paint off in those spots, but it had to be done!

 

Strange. Mines a 97. The 2000 motor that I have has the ground strap on it too. It attaches to the firewall right above the heater box to the left of the map

 

huh. with my batteries in the back, i ran a 6 gauge ground to the back wall of the cab figuring that would handle the whole cab (assuming there's at least a spot weld or two holding everything together. can't hurt to add another on, i guess. i plan to ohm all my grounds back to the battery first thing tonight, so we'll see where i sit with that.

 

Yes, there is a ground strap running from the back or the head to the firewall. I'll grab a picture this evening off my truck.

 

I would think that would have it covered JP. Idk it was just a thought. I hope you get this solved soon

 

ok, first i'd like to apologize for not contributing to anyone else's thread while i work through this headache, but i'm spending just about every second these days while not at work trying to sort through this. i post here so i can vent as much as anything. but of course, please keep any and all suggestions coming...

...as i'm almost entirely at my wits end. in two senses: 1. this is driving me crazy. 2. i am almost out of ideas on stuff to try.

so, last night, i checked all my grounds back to the batteries and everything was pretty consistent at 0.2 ohms. the consistency is good. does anyone think 0.2 ohms is not low enough. by V=IR, that's a 2 V drop on a circuit drawing 10 amps. i have cleaned and recleaned everything several times, though so not sure how lower it more.

after this i stuck my prob into the power wire of glove box light socket with the batteries disconnected and read only 48 ohms to ground. i expected it to be infinite. i then pulled this fuse and found that the incoming power to this fuse slot read to the same 48 ohms.

i then pulled every circuit except the PCM, IDM and instrument cluster circuit and the resistance went to infinite. figuring this was a good thing, i turned the key to on and still got the damn IDM relay clicking. i then put the glove box/other stuff fuse back in so that i could power up my AF interceptor guage/code reader (its dumb that the data connector power comes from this circuit, but that's the least of my problems). putting the fuse back in, resistance to ground stayed infinite, so that partial short (48 ohms) to ground was on some other circuit. ..again, a problem for another day.

at this point, i disconnected the batteries from the truck and hooked one up temporarily to the big power lug coming into the fuse box and one to the ground wires for the PCM IDM on the radiator support. same damn clicking!

i then pulled the instrument cluster itself. same clicking.

at this point i was disgusted and it was midnight so i quit.

So by my count there are only a very few systems that remain:
- instrument cluster wiring including connector through firewall
- ignition switch itself
- the engine harness or an engine sensor shorted or partially shorted
- the pcm or idm's themselves
- fuse box wiring

Plans for tonight, in order are to:
- add the big head-to-cab ground as suggested by Nick
- remove the ignition switch to supply power to the fuses and relays in the box as directly as possible.
- unplug the engine harness (anyone know if the pcm will stay on and fire up the IDM with no sensors input to it?)
- unplug the big through - firewall connector and try to jumper the connectors there to simulate key-switch-on-power and ohm-out all the pins on this.

if none of this solves it, i'm really screwed.

the other major thing i could do is rip the dash from my parts truck and throw that in there. that'll have to wait for the weekend though, as i'll need daylight for that...

ugh.

 

Maybe what you need is a bigger view of the systems. Do you have somebody near you that has a scan tool that will give you more options? If the IDM is clicking like that, it should be throwing a massive CEL, or some kind of code in the IDM and maybe the PCM that should give you a clue.

 

By no means am I an electrition so i wont even pretend to have a solution for you, BUT.. You did have the engine cranking and you cranked it quite a bit; was anything in that circuit that could have been damaged by a voltage spike or was the pcm, idm, etc etc all unhooked and you were turning the engine w a start button? Wonder if theres a way to test the idm and pcm out of the truck via multimeter.. Wiring is my least favorite, guess thats the right brain in me...

 

I called a diesel shop when I was trying to figure out what was wrong. I asked if they could test the IDM, with a computer or the like. I got told the only way to test it would be to put it on another truck and see if it works, that's what they told me to do. And they didn't want to do that I guess. I think swamps has a "test engine" or something like that when they tune up the IDM to a 140.

EDIT: I'd like to add something I just found.