Hi all,

First time here so thanks in advance for the help! I've got a '95 7.3 and replaced the glow plugs (Motorcraft), UVCH (aftermarket), and IPR (aftermarket) due to troubles starting in the cold. I did the IPR as while I was there I noticed the tin nut was fully off and the IPR was gunked up. I did have to rewire 3 of the 4 harness plugs due to existing damage. Following these updates, the truck idled fine for a few seconds on start, but then got very rough and threw a check engine light. I've been unable to get a code to show on Forscan.

After doing more research, I replaced the ICP (Motorcraft) as the idle wasn't affected by unplugging the ICP. The new ICP didn't have any affect on the idle.

I ran a buzz test and noticed that cylinder 4 seemed quiet. After running the truck with the valve covers off, it was clear no oil was coming out of cylinder 4 oil deflector so I figured it was time to do injectors.

Just installed Full Force Stage 1.5 injectors (with associated Jelibuilt tunes) and the problem still exists, although the idle sounds much rougher even on initial startup (see video). I did have some trouble getting the injectors in, and for several was barely able to push the injector down far enough to start threading the bolt. Buzz test now sounds all good and consistent. At this point I'm running out of things to check.

I do have a few potential ideas but don't feel great about any of them:
- I've heard bad things about aftermarket IPRs but I'd hate to spend >400 just to try a motorcraft one without isolating the issue first
- Bad HPOP
- Air in the fuel or oil systems that just need time to work out. Would love it to be this but I don't really want to put miles on the truck with it running so rough
- Maybe the injectors aren't fully seated (?) but I'm not sure how to confirm this
- I've had issues with the PHP chip before, so maybe I solved the main issue but the new tunes aren't working
- Trace all wires (?) although the buzz test did sound good
- Get a better code reader to read check engine codes

 

Do you know someone with a 7.3? if so, plug you IDM into their truck. If the problem moves to their truck, you have found your problem. My 96 crew had a miss, passed the buzz test , and had no codes. Turned out replacing the IDM cured the miss.

 

Thanks for the help. Do you know how interchangeable IDMs are? I do have another 7.3 but it's an '01 and automatic. Not sure if that matters.

Also, I did notice that the PHP chip is extremely close to this on the IDM, and may have moved it. Would this cause an issue?

 

The chip is mounted to the PCM. The IDM is under the hood next to the left hood support spring.

 

Any 7.3 model year will work. It will be a little more work to get to the IDM on the 01. You have to remove the drivers side inner fender lining to get to the IDM. As Cleatus pointed out, you have the PCM pictured.

 

If the IDM doesn't help, you can check HPOP health via Forscan monitoring the ICP pressure.

You can get an OEM IPR for less than $400. Mine came from dieselorings.

How long has it run since the injector install? There will be air in both the HPOP and fuel lines. Did you make sure the fuel bowl was full?

I'm not 100%, but I don't think air in the system is throwing the CEL. You need to find a way to read that code.

 

Thanks for all the responses and for the clarification in IDM / PCM. I'm going to be out of town for a couple days but will get to swapping the IDMs when I'm back.

@ibowl9 The issue with the IPRs is that this has the early 94.5-95.5 IPR with the edge filter so it's much harder to find motorcraft ones. I haven't seen any below $400 but can do more digging.

I did take this forscan screenshot prior to replacing the injectors and circled where the rough idle and CEL started. Not really sure what to make of it but let me know if anything stands out. I haven't driven the truck since the injector swap (as it's super rough and cutting out some) but I did crank it ~5 times for ~8 seconds prior to reinstalling GPs and then have done maybe 5 cranks after reinstalling the GPs but with the harness disconnected. Fuel bowl is full so I don't think thats causing the issue but oil rail could be a possibility.

 

I got back and tried switching the IDMs and both worked in the opposite truck. Glad to get some experiencing working with these in case something comes up in the future.

I ended up deciding to pull the aftermarket IPR (Carquest ac20082) and replace it with the OEM one that was covered in oil. After cleaning it up and reinstalling the OEM IPR, the truck ran perfectly!

Thanks all for the help.

 

I had almost the exact same problem also with a Carquest IPR. Replaced it with a Motorcraft, problem solved.