I have a 1993 F-Superduty 7.3 IDI diesel with a 5-speed manual transmission. For the first 9,000+ miles of my nomad life I had absolutely nothing go wrong with it.

Then at the end of my most recent haul it began stalling out on me on the highway. I start feeling a lack of power in top gear, and then all of a sudden it completely stalls out and the power steering goes and I end up stranded on the side of the road. For most of the stalls, I was able to start it up again on the first or second crank. A couple times it took bleeding the system at the injector lines and priming the fuel filter to get it going again.

So far I replaced the air filter and fuel filter (it was time anyway) and a couple old sections of lines that appeared to be leaking but it made no difference. Speaking with a couple mechanics yesterday, they mention a leak in fuel line seals or o-rings would most likely present itself as overnight intrusion/difficulty starting after sitting. This is not the case- it starts up fine and doesn't show any symptoms or stall out on me during city driving.

I suspect either the lift pump or the injection pump. I've read about installing a clear line on the lift pump and looking for air. A mech recommended removing the check ball in the IP and seeing whether it stalls out without it, but I've read that this isn't the best idea.
Any other ideas or low-tech ways to test these components?

 

It does sound like a failing lift pump, but your fuel filter light should be coming on, plus the IP should still suck up enough fuel on it's own to keep it at least running. It could be a bad fuel selector valve or pickup issue in the tank too. Does it act up on either tank?
It's odd that it restarted, indicating that whatever it is, isn't completely shot yet, and it's also odd that it had to re-prime the system too.

 

the fact it starts fine cold, and restarts after sitting for a bit suggests there is something in the fuel tank that is occasionally blocking the fuel pickup starving it for fuel.
if it was an electrical issue shutting the injector pump off, you would not have to bleed the whole system.

 

Oh, I had a reman IP do this once. I forgot it actually stalled out while driving once too. It wouldn't restart without letting it cool down. Because it was a reman under warranty, I didn't risk hurting it, but there's a trick you can try to speed things along; pour room temp water over the IP. If it fires right up, the IP is worn out and needs a reman. That part that causes this (the rotor head or something like this?) doesn't just get replaced during a reman I was told, unless there's a known reason to replace it due to cost I suspect. I had forgotten it was stalling on it's own sometimes, going down the road. I didn't have it in there very long. I swapped in my backup IP (that's now in my F450) and waited for the IP to get fixed. Got it back and no more problem. If this is what's happening, it could be losing it's prime because it can't send out the fuel it needs to the injectors when it's spinning of course.

 

I've never seen the filter light come on. Re-priming the system was a shot in the dark, honestly. Bleeding the lines has worked the other times. The selector valve is an interesting thought, hasn't gone wrong on me yet. When I got the truck there was a known rust issue with the plastic reserve tank that would make it stall out on the previous owner. Turned out to be a rusty sending unit from sitting too long with low fuel. Had that replaced last summer and the guy threw a new lift pump on at the same time.

I can't believe I didn't notice before, but the pump appears to be cracked?? I slapped some JB weld on it yesterday and drove 40 miles back to camp keeping rpms low (2500 max). Had no stalls on a stretch of road where it has previously stalled twice. It was tempting to drive it normally, but I really didn't want to get stuck in the middle of the night. Thinking I'll start with a new lift pump and then take it out for a proper test drive.

This could explain the filter light not coming on - the pump is working fine until the crack becomes an issue under load and the system depressurizes.



Nice trick! If the new lift pump doesn't solve it, I'll give that a shot.

 

That lift pump belongs right in the trash w/ a BB chevy block off plate, taking it's place.


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