Got word back from the shop - looks like rodent damage to one of the control harnesses under the regulator. They've verified that the issue is that the pressure is being bled off from the HPOP below to were the injectors fire as the electronics are having a bad day.
The rodent damage would also explain why introducing exactly the right sort of vibration reinstates the fuel supply.
berkeleying rodents.
Interesting. Unless you had to deal with it of course.
So it's all fixed and ready to go?
Curtis73 (Forum Supporter) said:berkeleying rodents.
If that was indeed the problem, it would likely be the second vehicle that was at least partially disabled by Northern Nevada rodents, with potentially some more help from the local ones here.
We already have an occasional "shop cat" - a feral one that hangs out here from time to time - but apparently I need a permanent one of those.
noddaz said:Interesting. Unless you had to deal with it of course.
Well, I mostly have to pay for the diagnosis and the hopeful fix.
So it's all fixed and ready to go?
Not yet, parts are supposed to show up tomorrow so hopefully it'll be done by the end of the week. At least it looks like the Diesel guy at this shop spent the time to properly reproduce and diagnose the issue.
Got the truck back this morning, with a new IPR, IPR wiring loom and, guess what, a new glow plug relay.
Starts fine now after it sat outside through the remains of Delta. So far, so good. Let's see what it's like if and when I take it for a longer drive.
What bugs me a little is that IIRC I had a local Diesel shop in Carson City fix a similar issue with what also centered around fuel injector pressure two or three years ago. Can't remember if they changed out the IPR, though.
In reply to BoxheadTim (Forum Supporter) :
Glad you got it fixed. Squirrels and rats are a pain in the butt. Also seems like it was in a place that would be hard to find without tearing some things apart.
Well E36 M3. After running like a champ since last October, the truck started playing up again. This time, it was clearly not running on all cylinders, although every time it would recover after a few minutes and start running normally again. 15mph top speed with my foot to the floor in a 40 zone is not my idea of fun.
Given the cost of the last repair I'm not particular keen on taking it to a shop again, but then again prices for stuff are nuts right now so replacing it with something that runs a tad better is probably going to be prohibitively expensive.
Either way this is beginning to feel like it's time to think about putting it out to pasture. I was hoping to wait with this until the end of the Alfa lease and then replace both vehicles at the same time, but now I'm not sure I can pull this off.
How many miles are on this thing? I've owned several powerstrokes of this era and worked in fleet maintenance with dozens of them. Never had one be a lemon like this. They are remarkably simple creatures.
I may just have to buy it from you and drop that 'stroke in my Fordzda Branger just for kicks.
Edit to add a thought. Somewhere on the downpipe from the turbo is a thing that should look kinda like a throttle body. It's an exhaust feedback thing that helps with warmups on a cold day. It is supposed to remain partially closed during light throttle and open up as you pass 1/4-ish throttle. You can sometimes notice it with a wee kick of acceleration and a change to the exhaust noise. Some guys unplug them and hook them up to a cable to make a po-boy's jake brake (but it doesn't really provide much decel torque)
Try wiring it open? It may be gunked shut.
In reply to Curtis73 (Forum Supporter) :
Odometer says about 318k.
There's a reason I'm know as a mechanical disaster area 
.
318k isn't old, but it is getting there. Most of ours in the fleet were retired when they were around 300k, not because they were dying but because someone at corporate had crunched the numbers on expected resale value vs. replacement cost vs. anticipated major repairs.
Diesels are typically rated by a B10 and a B50 metric. There is a mileage at which an engine statistically indicates that 10% of them will need an major overhaul and 50%. The B50 rating for a Powerstroke is 350k miles, meaning that of all the 7.3 'strokes that were tallied, 50% of them needed something major at or before the 350k mark.
Thanks. I'm not sure how major this is - it does feel like a few cylinders are not getting fuel, which is obviously Not A Good Thing.
Right now I'm debating if I throw it at the shop that fixed the previous issue again or if I finally call it a day and cut my losses.
Had to move the truck about 50 feet, and it misbehaved a couple of times, which I did manage to capture on video:
Once it goes into the failure mode it pretty much can't even move itself unless I absolutely floor it.
That sure seems electrical. As if the fuel relay can't keep the valve open or something (talking out my butt, just thinking out loud)
If it were mechanical I think it would be more consistent and wouldn't magically fix it self every time you restarted.
In reply to Curtis73 (Forum Supporter) :
Agreed, it does seem well defined in the sense that some injectors are suddenly not getting power. Right now I don't think it's a mechanical issue either - I know what HPOP issues feel like, and it's not that.
Makes me wonder if more rodents have been at the wiring again.
I have a 99 so maybe a little different - does your 96 have the same UVCH (Upper Valve Cover Harness) which powers the injectors and glow plugs? It's supposedly (according to the internet) common to have the connectors fail/vibrate loose over time and then you're not getting power to some of your injectors, which you said is what it FEELS like it's doing.
In reply to Brokeback (Matt) :
The injectors are mechanical by that point. 7.3L uses a computer-controlled injector pump that uses really high pressure oil to drive fuel pressure. That harness only controls the glow plugs which would create a kind of opposite effect. It would start rough and then smooth out as enough heat got to the cylinders. Good thought, though.
Curtis73 (Forum Supporter) said:In reply to Brokeback (Matt) :
The injectors are mechanical by that point. 7.3L uses a computer-controlled injector pump that uses really high pressure oil to drive fuel pressure. That harness only controls the glow plugs which would create a kind of opposite effect. It would start rough and then smooth out as enough heat got to the cylinders. Good thought, though.
That's not quite how the system works. The HEUI system does use high pressure oil to drive high pressure fuel but it's done at the individual injectors. The harness under the valve covers goes to both the injectors and the glow plugs and can cause issues with missfires. Here's a link to a description of the system Linky
There are a couple of other relitivly common issues that can cause missfires as well. Low oil level is the first thing to check. The other is the injector driver module (IDM). To avoid just firing the parts canon at it, it needs to be hooked up to a bidirectional scanner that speaks fluent Ford.
Oil level was the first thing I checked. It was about 25% above the minimum mark, so I did top it up. If it had any effect at all, it was making things a bit worse, not better.
I think the shop that did the wiring diagnosis and repair has a scanner that speaks Ford reasonably well. Which reminds me, I have to call them and see if they can tow it as I'm not risking driving it down there.
Do you know what part of the harness the electrical repair was made? I would try fiddling with those wires while it's running to see if it gets better or worse. Maybe a bad connection on the repair job?
I think it was the harness that runs under the fuel filter to the various sensor to the front of the motor including the HPOP pressure sensor.
Anyway, had to get the Alfa inspected so while I was at the local mechanic, I made the arrangements to get the truck towed to the shop at the same time. Spoke to their Diesel mechanic and he's pretty confident so far that's one of the typical issues for these trucks (IDM, injector harness or camshaft position sensor). So hopefully we'll get some more use out of the old girl. We'll hopefully know a bit more the week after next as they're a bit booked up.
Fwiw, this forum was awesome when I owned one of these
https://www.ford-trucks.com/forums/forum170/
Truck is still at the shop 
.
Looks like it developed multiple faults - the cam position sensor pigtail was in bad shape (may or may not have been rodents again), so once a new pigtail and a new OEM sensor went in, the fault wandered off to intermittently not firing one of the injectors (IIRC no 8, and apparently it's the same one every time). Current suspect is the injector harness, so that's next on the replacement list.
At this rate I may have to really start thinking about replacing this truck. None of the parts are that expensive fortunately, but the diagnosis time keeps adding up.
Got the truck back yesterday as they managed to track down the problem - turns out that it was the injector wiring harness under the valve covers that was damaged, and if the wires were vibrated just so, the harness would short out and not fire the injectors. Mad props to the mechanic who figured this out.
He also pointed out what whoever had been in there before - a specialist Diesel shop in Reno, NV - forgot to hook up a bunch of the glow plugs. That I paid that shop to change.
Of course the truck is already broken again - drove it to the local recycling center, noticed on the way back that it felt like on of the front brake calipers was dragging.
Then it started smelling like the brakes were dragging.
By the time I got home, it was smoking like one of the front calipers was dragging. Hey, at least that made it easy to identify which side was the problem.
I'm getting mild vibes of the universe trying to tell me something.
This poor truck. It's going to be new until you replace all the parts.
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