Picked up a 96 7.3 diagnosed by a shop with a bad lpop. I had a spare out of a motor I parted out sitting on the shelf and said why not. Tore everything down today, got things halfway put back together, and no dice. Still crank no start.

Hpop res was empty. If I added oil manually to the res, the truck would fire for a few seconds, then die, oil pressure gauge one the dash never moved. If I leave the screw on top of the res unscrewed- I do not get showered with oil.

Unplugging ICP does nothing.
IPR reads 55% when cranking
WTS light works fine, no blown fuses, both tanks 100% full of fuel.
RPMs show up on the dash while cranking per norm.

At this point I've narrowed it down to either a bad LPOP (still), bad front cover, or bad pick up tube.

Obviously, the first isn't the end of the world, the lpop I installed was working when it was last in a motor, but its possible it's crap now, I have another already that I plan to install tomorrow. Also planned on jacking up the rear of the truck (its already overfilled from filling the res a bunch of times), and seeing if submerging the pickup makes any sort of difference.

I'm curious if a bad IPR would have anything to do with this- but unlikely. I have 2 other 7.3s that are running fine I can pull an IPR from and swap it needed, to see if any changes occur.

any other thoughts?

 

 

After it dies, hpop level is empty.

HPOP isn't reading any pressure, because there isn't pressure to read. When it does fire, it fires to 2500 PSI and then dies to 0

 

There's no doubt in my mind the Lpop isn't working and nothing like ipr will cause it to not pump. If you change it again,pack the new pump with vasoline or assembly grease. Before tearing it down again,try this. I hear you when you say pan is already over-filled so you can drain it 2 quarts low before trying this or you can do this and not run engine at high rpm after it starts. Pour 2 quarts of oil in HPOP before trying to start. YES,you can pour in 2 quarts without overflowing. No sense doing this again if it start;s then dies,the Lpop or cover isn't assembled right or you will need a new LPOP.

 

One quart maybe in the hpop res. Sounds like the check valve is bad.

 

I had drained/refilled the res 3 times, every time the result was the exact same. It would start for 3-4 seconds, then immediately die. It would not fire again until oil was again added to the res. Rinse/repeat.

I took the harmonic balancer off, and put in another lpop. Front cover looked good on inspection, no grooves that caught on my fingernail or anything. I repacked the lpop with vasoline, and reassembled. I made sure everything was facing the right way and aligned.

She didn't fire up immediately, but I imagine I have a good bit of air in the system and will need to probably crank on it a bit before she fires, she's on the battery charger now.

If she doesn't fire after this, I'll jack the rear up and see if it does any good (doubt it), and I guess look for the check valve. Now- on the topic of the check valve, are we talking about the one directly behind the hpop? Or the one down by the oil cooler? I imagine if the lpop was functioning properly, she would still fire, it would just drain out and possibly cause rough running?

 

Go ahead and pour 2 quarts in hpop just before you try starting it,that will push a lot of air out of low pressure circuit and get it to running. The high pressure circuit will take a while to purge but shouldn't cause engine to die. Before grinding on it after batteries are charged,make sure fuel pump is working and air is purged from filter.

 

Have you replaced the oil filter to rule it out of the equation?

 

Have you replaced the hpop to rule it out of the equation? What I mean is maybe the wrong gasket was used.