2001 F250 7.3 PSD 180,000 miles on it. It is only running on 4 cylinders. I have replaced the UVCH with a brand new one from Ford. When I run a buzz test I get P1294 High Side open on the left bank. I have replaced the IDM with a known good one. I have replaced the PCM with a known good one. The buzz test shows that cylinders 2,4,6 and 8 are weak. However I disconnected the UVCH and ran the buzz test again and all 8 buzz but still 2,4,6,and 8 show weak. How can they even buzz at all if the harness is unplugged? I have ran the ohm test also and all the injectors show good with no shorts. I am about out of ideas. I have read many threads on this forum and cannot find any other ideas. Oh, I also took the wiring harness completely off the engine and checked the whole thing and wired in a new UVCH connection from Ford while I was at it. Any ideas?

 

It is physically impossible for the 2,4,6,8 injectors to buzz with the drivers side UVCH disconnected.

 

That sounds fishy. Where did you perform the ohm test at? Ohm everything out at the IDM connector. If there are any anomalies, start working your way down the harness in towards the engine to find the issue.

 

I agree 100%. My question is, What is buzzing? It is buzzing on those cylinders but very weak. It is the same with the harness plugged in or unplugged. I don't understand how that can be. What is making the buzzing sound?


I have ohm'ed everything from the IDM connector using the picture you supplied multiple times. They all come out at 2.9 or 3.0. The open circuits test out good also. I just had a thought, Is it possible that all checks out good and the connector is just not making good connection when I screw it into the IDM. Can those connections get spread out and cause this anomaly?

 

With our 16-20yo trucks, that is certainly a possibility. Try spraying the contacts with contact cleaner first and see if that helps though. Have you run a contribution test to see if the weak buzzing is having a practical effect on engine performance? What led you to run the buzz test in the first place?

 

The IDM is in a very bad place, it gets "pressure-washed" with mud on a regular basis. Contact cleaner and dielectric grease is my modus operandi every time I work with a vehicle connector (except the spark plug circuits).

He can pass the solenoid ohm test, yet still be shorted to the valve cover at the 42-pin connector.

 

The truck is only running on 4 cylinders. I have done a LOT of reading posts on this forum so I replaced the UVCH first. At the same time I ohm'ed all the circuits from the IDM out. That did not fix it so I ran the buzz test to see which injectors were not good. That test shows the whole left bank shut down. I removed the IDM and PCM and installed them into another truck that I own. ( 2000 f350 7.3 SD ) Both of those worked in that truck along with another spare that I have of both the IDM and PCM. I then removed the wiring harness from the engine and took the casing off it and traced all the wires. This is when I soldered in new UVCH connectors from ford. I reinstalled everything and ohm'ed everything again to make sure before I connected it back to the IDM. I ran another buzz test with the same results. I then replaced one of the injectors to see if that made any difference. It did not.

In my mind the only things that can cause this are 1. UVCH, 2.IDM, 3. wiring, 4.injectors, 5. PCM, 6. HPOP ( checked that also and it is firing the other 4 cylinders just fine.) Is there anything I am missing?

I removed the wiring harness and rewrapped everything from the 42 pin connector to each engine component. I have been chasing this thing for 2 months. I will take the IDM connector off and spray it with dielectric grease. That is a good idea.

I really appreciate the help on here.

 

What is odd in your situation is that the DS bank's injectors are still buzzing when the UVCH is disconnected. Are you sure it's the injectors themselves buzzing? It may be an electrical short arcing somewhere. The IDM does put out high voltage after all. See if you can isolate where that UVCH-disconnected buzzing is coming from.

 

I don't believe it is the injectors themselves but there is a buzzing coming from somewhere. I cannot figure out where it is coming from. And the buzz on those cylinders does not change with it plugged in either.
Buzz test goes like this:
All 8 sound loud.
1,3,5,7 sound loud
2,4,6,8 buzz but very low - even when the UVCH on that side is disconnected. I know it is impossible for the injectors to be buzzing but I cannot figure our what is buzzing.

 

I think that's your answer right there. Use rubber vacuum line to your ear and run the bizz test while figuring out where the 2, 4, 6 & 8 buzz is coming from.

 

Just an idea , But maybe do the buzz test at night with engine compartment is dark. Might be able to see a spark.

 

That is a good idea. I will try that tonight.
Thanks

 

Good idea too. I will do that when I get home today.
Thanks

 

That's genius-level thinking.

 

What did you find?