Hi all,

I had an issue with my 7.3 excursion recently. It died on the road and we towed it to my buddies house. We eventually tracked it down to the IDM (Starter cable had also broken at the same time). Now when I got the new IDM from advance auto ($700 later) I was going through and ohming the harness on the IDM side. The Driver side bank of injectors all ohmed out at 3.6 ohms. The Passenger side had injectors 1,3,5 ohm out at 25 ohms, and injector 7 ohm at 3.6. I was going to pull the valve cover and check the UVCH, but my buddy who has worked on these for a while told me to just stick the IDM in. We did that and the truck fired right up. No rough idle, no loping, no breakup, purred like a kitten.

Now I'm still wondering why I was getting those odd readings on the UVCH. The IDM was replaced 7 months ago because it was the original IDM (2001 Excursion) and it had gotten water in it. The replacement IDM was totally dead, buzz test totally failed, nothing. I'm not sure what killed it, if maybe the starter cable grounded out and passed current through the IDM and fried it. Has anybody seen this behavior before where the injectors have bad ohm readings but the truck runs fine?

Also, most of the truck is original, and it has <70k miles on it, so not sure if there's stuff just going bad due to age.

Any help is appreciated.

Thank you.

 

man first off I just want to say at 70,000 miles I am super jealous! Were you able to check and read codes? Did you try several times to get a good reading? I find that kind of odd also. Others will be along shortly to chime in

 

P1670 and P0603 are the ones I remember. There was one where it said PCM cannot communicate to IDM. When buzz test was initiated there was absolutely nothing. None of the injectors buzzed. 70k might be good, but in those 20 years this truck has been in the shop about 15 times. Never ending problems with it.

For the ohm readings. I probed them 5 times. I made sure to move the probe leads around in case there was any oxidation. Ohm reading held steady at 24.7 for each of those injectors.

 

Any ideas on this? I need to do a road trip with this truck pretty soon and don't want to be broken down with another fried IDM.

 

25 ohm is quite a bit off. I feel like if that were the case you would have some rough running. If it were me i would dig in further. From what i understand you are reading ohms from the idm?
I would check them from the 42pin connector and the 9 pin connector at the valve cover. Report back what you find.

If you suspect the passenger side uvch pop off the valve cover and take a look at the connector. Are any of the pins burned or melted? Was the connection tight?

Advanced auto sells the carquest idm and i think it comes with a lifetime warranty. I feel like most rebuilt or reman parts don't last as long as oem. Unless you find an individual that does this, or specialize in this. Mass produced or mass reman parts get a standard in and out the door treatment.

I like my excursion. The wife likes to drive it in the winter. And she's always driven it to estimates and work apts. The 7.3 has its nuances but i trust any of mine to drive cross country.

 

I replied to your thread in the Excursion forum but I see that there's a little more info in this thread.

It could be a short in the UVCH with the off ohm readings, or a poor connection. Did you take the ohm readings from the IDM connector? You could try at the 42 pin and then the outside of the valve cover and see if you get the same readings. Check the 42 pin connection where the wire group lays on the driver side valve cover, a common spot for chafing. If you get those high ohm readings from all locations then I would pull the cover and take a look at the UVCH for poor connection, burns. Inspect the gasket pins and UVCH, I would think that is your issue.

I'm not an electrical expert, but ohms are resistance. High resistance can be caused by loose connections or shorting wires which can cause a gradual worsening issue as the connection or short deteriorate and not necessarily an immediate failure. You could have had bad luck with the last IDM having a short life, but that is pretty soon to be swapping again so I would lean towards thinking that something caused it, not just a bad IDM. I just went through the IDM replacement. Mine was the original from 2000 with 367,000 miles on it, and it lived 1 mile from the beach in Florida its whole life. If you're on your 3rd IDM in 70,000 miles then I would think you have a wiring issue somewhere.

 

I measured resistance at the IDM harness, with the IDM disconnected. I pulled the UVCH connectors and nothing looked burned on the outside connectors, but I have not popped the valve covers. I got the carquest IDM from advance auto with a 3 year warranty. I just drove this truck cross country, but it has constantly been in the shop ever since it was bought by my parents new 20 years ago. I know the 7.3 is bullet proof, but every supporting system has **** the bed on us.

 

I just saw your post on the other thread. I changed out the CPS. The original one was in there and I put a new motorcraft in.



I performed all tests on this sheet, that's where I found high resistance on injectors 1,3,5. I checked passenger and driver side UVCH on the outside valve cover connections, no burns. I ohmed it from the 42 pin connector and found those high readings. I'll look for chafing today

There was one wire, gray with a red/pink stripe on the idm connector, that had a small bit of chafing on it, but the conductor was not exposed. I can't perform another buzz test right now, I used my buddies scan tool to do it.

If I have chafe's/shorts in the wiring harness, what's the best way to fix it? Should I replace the whole thing, or just cut out the bad sections and splice some new wire in?

Thanks for the help.

 

I got this on amazon that connects to a laptop to run Forscan for codes and testing. It would be worth it to have around and it was under $20. I would think that if your truck is currently running fine then you might not see anything come back bad on the buzz test since your injectors are functioning, albeit with high resistance. I'm not sure if that 100% true though, when I had issues I lost the whole passenger side. Do you have an SES codes right now? I would check the ohms again from the external valve cover pins and if you get the same results, then I would pull the cover and replace the UVCH you may have issues that you cant see from the outside. If you get spec ohms from there, then I would look between the 42 pin and eternal VC connector for shorts/chaffing.


I personally did not end up with any chaffing or shorts, but I have seen others electrical tap the individual wires with damaged casings and then wrap a tubing around the entire harness where the chafing is.

 

So I did have a SES light on during the 1300 mile drive I did, but I attributed that to needing an oil change, seeing as she is due for one. I believe it comes on at 3k miles for an oil change, correct? It may have been the IDM/UVCH/Wiring harness that caused the SES code to pop up and it just coincided with the oil change mileage.

 

No, the truck has no idea when the oil was last changed. Or if the oil is dirty. But if the oil gets too dirty or thin it can hurt your fuel economy and performance.

If your rig is running well maybe leave well enough alone. If it has a miss or performance/economy is suffering i would pull the valve cover. You need an 11mm for the cac tubes. And a 13mm for the valve cover. A 13mm swivel and different extensions. The passenger valve cover will sort of roll down and out. The connection under the valve cover can be loose. But dont just push it together, you want to inspect that pigtail for burt pins. If it looks ok you can use the quarter trick to keep the connector tight. See 50 cent mod.

 

I just had a chance to go out and take a look. I pulled the 42 pin connector on the driver side valve cover. There was chafing on the aluminum wire wrap, but the insulation on all the wires is intact. Does anybody know where I can find a pinout of the 42 pin? I'm trying to work my way back from the IDM. If I get good ohm readings on the 42 pin, and bad ohm readings on the IDM, then my issue is between the 42 pin and the IDM. If I still get bad readings, then I'm pulling the valve cover.

 

 

So I found this pinout for the 42 pin connector.




All driver side injectors ohmed out at 2.8 ohms. Injectors 1,3,7 ohmed out at 4.3 ohms, and injector 5 ohmed out at 3.1 ohms. I'm guessing there might be an issue with the UVCH, but that's a far cry from the 25 ohms I pinned at the IDM the other day.


Just saw your reply T-wood. Thanks for the diagram.

 

You can now check resistance from the other side of the 42 pin connector to your idm. Again if you feel there is an issue.
yeah 25 ohm is alot and i really feel like you would notice that in the way it runs. Its really easy to have a lead on the wrong pin. I have and i usually figure it out because of the results.
What was your fuel economy on your 1300 mile trip?
I calculated a 1200 mile trip in my 7.3 van. All highway average speed was probably in the 77-80 range. I got 18.7 mpg. My van is probably 2k lighter than my 4wd excursion.