Hello all.
I'm going to apologize in advance for the book I'm about to write but I wanted to lay out as much information as possible to give the people that have got more experience than I dealing with this more to work with. I have spent the last couple months scouring the web trying to find the solution, because I don't like to post in a form about something that's been posted about 500 times before. Nonetheless that's probably exactly what I'm doing I'm just not realizing it.
I'm trying to figure out a running issue on my dad's 99 F350. Based on the build date of 06/98 and the build date on the engine of 04/98, I have to think that it's considered an early 99 (for what that's worth). It has roughly 220k on the clock, and he put about 75k of that on it. As far as we have been able to determine, the engine is stock and not been tweaked or modified in any way and other than basic maintenance, it's not really had to have anything done to it. The engine has never been overheated while my father is owned it, and other than an issue with the transmission that had to be repaired a while back it's been relatively trouble free. Now on to the issue.
About a year ago he brought it to my attention that it had developed a miss at idle. It was without any doubt a dead cylinder mist, and not an erratic misfire of any kind. I was too busy to get into it at the time because I was helping them prepare to sell the family farm and move into town, so the truck sat until it was moved to their new place and sat inside the garage for 6 months or so. I started it up to move over to where I was going to work on it, and surprisingly it started perfectly fine and didn't misfire and ran great. But after driving it almost to the destination which is about 10 mi away, I noticed that at idle the misfire had returned. That wasn't really a big shock because problems never ever fix themselves. Or at least in my experience. My first thought was to run a cylinder contribution test. I do have an AE dongle and software. Every time that I attempt to run the test, as soon as it enters into the test the engine stalls. It will also usually stall if you have the engine revved up and then release the pedal where it will come down to idle and then quit. No check engine light, no fault codes. Oddly enough, when you started up cold you can't tell that it has a miss. It's only after the engine starts to warm up that you can slowly feel the miss become noticeable. That's why I thought that the o-rings could potentially have been an issue because of viscosity or flow changes in the oil as the oil warmed up. Given the miles on the engine, I thought the replacing the rings on the injectors might not be a bad place to start. After doing that I also went ahead and did an engine oil and filter change and change the fuel filter as well. These things made no difference. Just for the heck of it, I went ahead and pulled out the inner fender well to get to the IDM. I'd run into a 7.3 before with a no start condition and turned out that the IDM and failed. That's why I have the AE dongle and software. Even though there was no check engine light and no codes I went ahead and did an ohm test on the harness going from the IDM to the injectors and to the glow plugs and everything checked within specification. I've also run the truck with a valve covers off to observe the oil flow out of the injectors and although some of them are a little bit difficult to see they all look to be about the same and I didn't notice any particular one or ones that were significantly different than the others. I also did a buzz test and there were two injectors that sounded a little bit different than the others but honestly I've never really done a buzz test on one that's got issues to know what constitutes "bad". While I have the valve covers off and it running I also observed the valve train just to make sure we didn't have a cam issue or anything of that nature. I also unplugged the harness at the ICP sensor and the sensor is nice and dry inside. I also checked the fuel pressure at the filter housing and it was right at 65psi.
I'm kind of scratching my head as where to go at this point without just throwing lots of expensive parts at it. I don't want to go swapping out injectors or other rather expensive components just trying to shotgun it to find the problem. I'm hoping that what I've described might ring a bell with somebody. I've scoured the internet for the last several weeks and check the variety of things that I found listed for similar symptoms and haven't really had any luck.
If anyone has any suggestions I would sure appreciate it.

 

With AE you can check cylinder rotational velocity pid for each cylinder all at once, which is actually what the pcm does during the cct. It should help zero in on the offending cylinder. Another option is to run the truck with valve covers off and unplug injectors one at a time and see if it stops. Then possible swap that injector to a different location to see if it follows. If it follows then likely failing injector if it stays then something else going on. Air in the fuel will also cause knock and give no codes. Have the in-tank mods been done(hutch/harpoon)? The factory fuel pick up in the tank is a known and well documented problem area.

 

You have done alot of great troubleshooting and eliminated much - nice work!

Scanned with AE - no codes, engine stalls when CCT started
valve covers off - verified oil flow from each
buzz test - 2 injectors sound different
ohmed harness from IDM to injectors/GPs with good readings
fresh oil (assumed full), fuel filter changed
ICP connector is dry
Fuel pressure at idle is 65psi

udsuth78 has some good suggestions to narrow down the issues.

Is the tinnerman nut tight on the IPR? Your symptom of "It will also usually stall if you have the engine revved up and then release the pedal where it will come down to idle and then quit." points to a possible IPR issue. If the sensors are original, not a bad idea to have a new motorcraft ICP and IPR on hand to swap out. You can clean and rebuild the IPR instead if you want, but note that the IPR solenoid can fail as well.

 

You can try running it with the ICP sensor unplugged. The PCM will use default values. If it runs better, consider changing the ICP.

Here is a thread where a guy with an early 99 had the CCT stall the engine - new ICP fixed it. ICP and IPR are two critical sensors for these rigs.

https://www.thedieselstop.com/thread...engine.660041/

 

Just to be "Mr Picky" the IPR is not a sensor, it's a valve. Still could be the problem in two ways; first the tin nut holding it together could be loose/gone, and second the magnetic coil on the IPR solenoid can fail when hot. You can test it with a multimeter, resistance should be about 10-11 ohms, see below.

Does the CEL come on during the dash functionality check when the truck is started?

 

To my knowledge, nothing has ever been done to the pickup in the tank. I will have to look into that. I will try checking cyl contribution by unplugging the injectors one at a time. I guess that's the more modern method of what I used to do such as cracking the lines on the mechanical systems. I usually work pretty well for them.
Thanks!

 

I don't remember the solenoid on the IPR being loose my unplugged it to check the wire and connection to it. However, I do remember that little silicone seal this to keep moisture out actually being kind of gooey almost like something was leaking through and getting to it and contaminating it. but the way that IPR is designed I couldn't hardly see that happening. However I'm going to do what you suggest and unplug the IPR sensor and see what happens there.
Thanks!

 

Thanks. I'll take a look at this post from the diesel stop and also check the IPR and try running it unplugged like you suggest.

 

I haven't done an own check on the IPR solenoid, but I am pretty sure that the solenoid itself is tight.
But yes the check engine light does come on when it does itself check in the beginning. There were also no pending codes.
Looks like I've got a multiple things to check this weekend on this truck.
Thanks!

 

Thanks for the replies everyone. I'm going to get back into it this weekend and maybe I'll make some headway. The last couple weekends I've spent I feel like I accomplished nothing but now I think I'm going to make some more headway and figure out what's going on. I'll post an update with what I find good or bad.
Thanks again everyone!

 

They are talking about trying to run with the ICP unplugged, not the IPR. It is located towards the front of drivers side head. This is also where to look for oil in the connection.

When they talk about the IPR being loose they are referring to the timnerman nut on the back of it. I got this photo from another post here on FTE by HKusp.