IDM Code - Page 2 - Diesel Forum

klhansen · 10-04-2009, 08:44 PM

Check post #10 in this thread

TXF-250 · 10-05-2009, 02:13 PM

Quote:

Originally Posted by klhansen

You got it.

To do that, you'll need to disconnect the other end and put your meter on each end of each wire in the harness. You'll have to match wire colors with pins on each end. That's called a continuity test to see if that particular wire is intact from connector to connector.

To check for shorts between other wires is a bit more involved as there are lots of combinations. Again, with both ends disconnected, check with one meter probe on the pin you want to test, and the other probe on all the rest of the pins in sequence. While you have the meter in place (hopefully reading infinite ohms) wiggle the harness along it's entire length and watch for the meter to go to zero ohms. That indicates that the insulation between the two wires has chafed and the conductors are making contact. - But I wouldn't try that test unless you've got some indication that it's occuring, as it's fairly unlikely.

The other test is to check for short to ground. Meter probe on wire being tested, other meter probe on a ground, and again wiggle the harness bundle.

Alright well to dive into this a bit deeper...

Will I still be testing resistence (meaning do i keep the meter on the same setting I was using to ohm out the injectors)?

Also, you said to disconnect each end that goes into the valve cover in order to check the wiring harness...the problem i see with this is that theres a lot more in the bundle than just VC wires. Do I leave the rest of it hooked up?

Lastly, when you talk about checking all of the "combinations," are you saying to put one end on the harness that goes to injector 7 (for arguments sake) and then put the other end on all of the other in the harness for injectors 2,4,6, and 8?

Thanks again for all of your help!

klhansen · 10-05-2009, 05:48 PM

To check the circuit for Injector #1 say, pull the connector loose from the valve cover, locate the pin for that injector and not the wire color. Go to the 42 pin connector on top of the VC and pull that loose and find the pin with the same wire color. Put your meter (still on ohms) probes on each pin on that wire. You should get very low reading (like less than 1 ohm) unless there's a break in the wire. Repeat for each injector and for the common wire in the center. You can leave the other engine sensor connectors hooked up. Just don't do the test with the key on.

Then it gets hairier. From the 42 pin on the VC, you have to pull the IDM connector and find the matching wires on each end. The IDM connector is a PITA to get at, as you have to pull the fender liner loose.

When I say there are lots of combinations to check for on a short to another wire check, there are nearly 42 circuits going thru the 42 pin connector (some are empty), so for each circuit, there are potentially 40 or so wires that it could be shorting to. To do a complete test, you'd have to put your second probe on each one of the adjoining wire terminals for each wire in the bundle.

Short to ground isn't a big deal though, as you just test from each circuit to ground. For all the injector circuits, that'd be a total of 10, 5 per side.

TXF-250 · 10-10-2009, 05:57 PM

hello again...

in the process of ohming out the wiring harness right now.

How do I figure out which wire on the harness is ground?

UPDATE: I finally matched up the pin on the passenger side vc to the one on the main harness mounted on the drivers side. Got a reading 0.7 ohms...moved wires around and jiggled everything...still stayed at 0.7. I guess this means that the wiring harness is ok? Now, do i have to go from the Driver's side main harness to the pcm, and then from the pcm to the idm? Or is it from the harness straight to the IDM?

klhansen · 10-10-2009, 09:22 PM

0.7 ohms indicates a good circuit.

The injector circuits go from the VC connector, to the 42-pin, then to the IDM. They don't go to the PCM.

TXF-250 · 10-10-2009, 09:25 PM

Alright then, so i guess that means perform the same test i performed on the injector circuits, but now on the harness from the IDM to the valve cover. Should i expect to see about the same reading?

If it passes the test, does this then mean the IDM is bad?

klhansen · 10-10-2009, 09:31 PM

Quote:

Originally Posted by TXF-250

Alright then, so i guess that means perform the same test i performed on the injector circuits, but now on the harness from the IDM to the valve cover. Should i expect to see about the same reading?

Yes

Quote:

Originally Posted by TXF-250

If it passes the test, does this then mean the IDM is bad?

That's a possibility. If you have a buddy with a 7.3L, you could try your IDM in his truck and see if the same symptoms appear. That'd probably be easier than checking the harness from the 42-pin to the IDM. The IDM connector would be a PITA to get at.

TXF-250 · 10-11-2009, 02:49 PM

I unfortunantly do not have another IDM to try out, so i guess I'll be pulling the fender down to get to that harness. I'll give this a try and see what happens. I'm just gonna have to clip one terminal to the VC harness and then fish the wire through to get to the other end of it. I'll post back with results.

UPDATE: I went out there and pulled the fender down and got my volt meter on either end of that harness...after messing with the settings finally got a reading...0.8 ohms...

I think this pretty well confirms that wiring harnesses are good...

Your thoughts? I'll wait for a response before I start talking IDM's

TXF-250 · 10-12-2009, 04:29 PM

Hello again,

I just got off the phone with Auto Computer Exchange out of FL and was discussing my problems with them and inquiring about a new IDM. They felt that based on what I was telling them, this seemed to be a PCM issue and not IDM. They said the IDM would cause you to lose and entire bank of the engine and not just 1 injector.

How can i test the pcm or wiring harness to it?

Does this seem right?

TXF-250 · 10-13-2009, 01:40 AM

bump...

klhansen · 10-13-2009, 01:45 PM

Quote:

Originally Posted by TXF-250

Hello again,

I just got off the phone with Auto Computer Exchange out of FL and was discussing my problems with them and inquiring about a new IDM. They felt that based on what I was telling them, this seemed to be a PCM issue and not IDM. They said the IDM would cause you to lose and entire bank of the engine and not just 1 injector.

How can i test the pcm or wiring harness to it?

Does this seem right?

I'm not sure I'd agree with them, but they do repair them.

Where are you located? If in Texas (guessing from your username), there are probably a million 7.3L's running around there. I know there are lots of TDS members, and one of them may be willing to help you out by loaning you an IDM. try the Power Stroke Help Network - 1994-1997 Power Stroke FAQ, and see what you come up with. I'd hate to see you buy an expensive IDM and/or PCM and still have the same problem.

I admire your persistence in checking continuity between the IDM and heads. That's something I'm sure I wouldn't like to tackle.

TXF-250 · 10-13-2009, 11:16 PM

Yea thats a good idea...hopefully I can find someone. I am indeed in TX.

I talked with Jody at DP Tuner today, and he is just about as perplexed as everyone else I've talked to. He said the chances the pcm or idm are messed up are just really small. He said it was certainly possible, but just still doesnt seem that likely. He said that a lot of times he's seen that code, it has had to do with the injector itself. Appearantly there is some sort of circuit on the top that is gapped (kind of like a spark plug) and that over time with rebuilt injectors (which to my knowledge they are not) that gap can collapse. He said if it does, you'll have an open circuit (high to low side open).

He said that before I go and buy a pcm, to try and swap the positions of injectors 5 and 7 (since 7 is the culprit), and run the buzz test again. If it moves to cylinder 5, that's a sure sign its the injector.

Do you think this is a route I should take? I dont know how I feel about R&R injectors...it seems like its too much for me to take on. Your thoughts?

klhansen · 10-14-2009, 05:10 PM

I'll agree with Jody that IDM's and PCM's don't go bad all that often, but it does happen. I've had 4 bad IDMs go thru my hands (not mine, but from trucks in the local area).

Anyway, his suggestion on swapping the injector positionis is a good one. It's not all that hard to do. Just make sure you use new o-rings on them and be sure to get the oil that'll drain into the cylinders out before you try and crank the engine. Swamps Diesel has a how-to. http://www.swampsdiesel.com/ look at the link to the left.

You could also just swap the solenoids on the top of the injectors and accomplish the same thing. That takes removing just the 4 torqx screws on each injector. If the code moves to the other cylinder, then the solenoid itself is bad, regardless of what your ohm test showed. It could be breaking down under the high voltage, but the low voltage of the multimeter doesn't show an open.

TXF-250 · 10-15-2009, 10:43 AM

Quote:

Originally Posted by klhansen

I'll agree with Jody that IDM's and PCM's don't go bad all that often, but it does happen. I've had 4 bad IDMs go thru my hands (not mine, but from trucks in the local area).

Anyway, his suggestion on swapping the injector positionis is a good one. It's not all that hard to do. Just make sure you use new o-rings on them and be sure to get the oil that'll drain into the cylinders out before you try and crank the engine. Swamps Diesel has a how-to. Swamp's Diesel Performance look at the link to the left.

You could also just swap the solenoids on the top of the injectors and accomplish the same thing. That takes removing just the 4 torqx screws on each injector. If the code moves to the other cylinder, then the solenoid itself is bad, regardless of what your ohm test showed. It could be breaking down under the high voltage, but the low voltage of the multimeter doesn't show an open.

Ok switching out the solenoid, I feel comfortable doing...removing the entire injector just seems a bit shaky. I wouldnt mine doing it with someone helping me, but along just scares me. I think i can handle switching out the solenoid...plus...thats the only part of the inector thats electrical right?

klhansen · 10-15-2009, 04:52 PM

Quote:

Originally Posted by TXF-250

...thats the only part of the inector thats electrical right?

Correct.

What does the buzz test sound like when you run it? All injectors should buzz first, then each one individually, in numerical order. They should all sound pretty much the same. If the #7 sounds weak, or the buzz sounds like it's coming from the IDM when it's #7's turn, then that injector solenoid is sure suspect.

The buzz test actually applies the high voltage to the solenoids so is a different test than just measuring the resistance of the solenoids.