99 7.3 running on 4 cylinders

[Wulf202]

I've been lurking here for years reading and learning just now created an account after struggling with this issue for weeks. I'm going to try to give as much detail as I can in hopes that you all have ideas.

1999 7.3 (late engine and no mods/chips) 4x4 auto. at 225K I did the injector cups with injector o-rings, injector shim kit, glow plugs and GB valve cover harnesses . I put 2500 miles on it, highway with light towing. Had a stutter in the middle of nowhere, diagnosed it running on 7, unplugged each valve cover harness, isolated it to passenger side. I used the pig tail from the GB harness replacement I threw in my tool box to ohm each injector, #3 was open. So I presumed a bad solenoid, none of the parts houses had anything to help so I limped home.

Got a new harness and injector, verified Open circuit on injector #3. Removed valve cover, removed harness and injector. Injector ohms good (3.2ohm), harness ohms good. Applied heat to injector solenoid, ohms good (2.9ohm). Replaced both injector and harness anyways. Truck runs on 4 cylinders after a very hard start when plugged in.

Cussed a lot

Swapped in a good IDM, no change. Swapped PCM, no change. Removed the engine wiring harness and ohms good, removed wrap and no visible damage. Checked for rubs at the driver's valve cover wiring harness to IDM, found none, armored it with heater hose anyways.

Cussed a lot

I took it to a shop who charged me $275 to guess at some things I had already done, when they were chasing their tail, like I was, I brought it home.

Pulled the passenger valve cover, replaced 3 remaining injectors, verified the second new valve cover harness is good. 1,3,5,7 injectors at 3.0ohms.

Cussed a lot

Used the GB tech bulletin #103 to pin test the harness, all within spec. Verified ground (pin 26) and neg battery terminal have continuity. (yes I should have done this sooner but live and learn)

Cussed a lot

What am I missing?

 

[Oledirtypearl86]

Did you get a scanner and buzz test the injectors also a compression test and when idling does it smoke a lot

 

[Double-S-Diesel]

check the fuel check valve on the fuel inlet to the head.
also have you checked fuel pressure in general

 

[lotzagoodstuff]

Welcome aboard. First and foremost, I think you are looking at and doing everything you should based on the issue you are describing. It also sounds like you did a lot of the preventive maintenance when you shimmed the injectors, cups, orings, glow plugs, etc. Sometimes you can do all the right stuff and an electrical gremlin can persist.

I have heard and read a lot of really bad things about anything but OEM (International/Motorcraft/Alliant) harnesses and UVCHs. I recently converted my old OBS dual connector UVCHs to the single plug style and I read a lot about it as there were wildly varying prices for the replacement wiring pieces. The 7.3 big hybrid injector suppliers say that the most common problems for poor performing 7.3 injectors is the use of non-OEM injector UVCHs. They usually talk about Doorman as the worst brand, and there's some rumors that some products are using aluminum wiring where the OEM product has copper. Lots of stories about new injectors running bad out of the box due to poor quality aftermarket UVCH and injector harnesses.

Have you run it with the valve covers off and really poked around the connections a bunch while the truck is running? Again, I think you are taking a very solid approach so far in every way with the possible exception of the parts you used, but that's speculation. As good as everybody says the 7.3 PSDs are, they have their faults just like everything else.

Don't feel bad about the cussing a lot. I've had the fuel bowl out of mine 4-5 times for intermittent leaks. I really do hate that f*cking fuel bowl.

 

[Wulf202]

Buzz tested in the parking lot of the shop that told me it was impossible to buzz test it. I should do it again the the garage tomorrow after the 3 new injectors and without background noise.

No smoking shortly after it starts.

I don't have a compression tester adapter at the moment but I'm working on it. Though it seems unlikely I lost compression in all 4 cylinders on the right side.

I will check the fuel if I find the new injectors are pushing oil thru them. Fuel pressure is ~50-60psi according to pillar gauge, it runs on 4 and will rev and drive, though gutless.

I got GB UVCH because they're supposed to be the best aftermarket harnesses and are built like OEM (maybe just from the same factory). There was no change after I replaced the nearly new harness with a brand new one, also all injectors ohm good from the harness and the IDM connection. Though the shop claimed to have found a small amount of resistance that went away when they unplugged the passenger side but I have been unable to recreate it and didn't want to pay $125 an hour for them to chase it down.

I have ran it with the valve cover off, poked around, wiggled, stood on one leg and all the other shade tree tricks I know.

It doesn't seem to be sending power to the passenger side harness at all. I cobbled together a contribution test with an old UVHC I chopped, the pigtail and some alligator jumpers and not a single injector did anything on that side. I should try to read the current at the harness. I've verified ground from injector plug to neg battery.


Is it possible an error in the drivers harness would short the passenger side? I haven't pulled that valve cover. From looking at the wiring harness it doesn't seem like that's possible as all the wires go to the 42 pin connector individually

Is it possible this is a sensor elsewhere? IPR? CPS?

 

[Wulf202]

After multiple hours in the garage going over everything again, I'll spare you what I did because I started over from square one.

The original diagnosis on the side of the road was correct #3 injector was bad after 225k. So was the replacement part, I put the original #7 injector in #3 and the other 3 cylinders have refurbs, runs fine now.

Cussed a lot.

Thanks everyone for all the help.

 

[lotzagoodstuff]

Congrats on solving your PSD issue