I've read several threads describing what i am experiencing in my 7.3 N/A IDI. I will drive for roughly 20 ish minutes (Less with heavy load) and then i suffer a total loss off power like it ran out of fuel. Upon restarting the engine it becomes sluggish and the worst case my foot is on the floor and i struggle for 50 mph. Actually loose speed when climbing a hill. I have good delivery. When you push the Shrader valve on the fuel filter housing it will shoot fuel across to the other valve cover with out issue. I struggle to see how it could suck air through the housing as it is a pressure fed system. I just replaced the fuel filter mounting body as the old one leaked out the heater plug. then this issue popped up. was not present before i changed it. had driven it several hundred miles in a day. I suppose that answers the question but the technical part of me wants the "why" answer.

 

If the mechanical pump isn't able to keep the pressure up under load/high fuel demand then you could have air intrusion at the new filter mount, or elsewhere. The likelihood is that the problem is related to the replacement, either the mount itself, the lines, or something that was disturbed during the replacement.

 

Make sure you keep an eye on your oil level when troubleshooting this. The mechanical fuel pumps on our IDIs are known to rupture a diaphragm and pump fuel into the crankcase. This actually happened on my 6.9l. I only realized it was a problem because I was monitoring my oil level.

 

How old is the injection pump? An old worn pump might have decent tolerances when cold, but loosen up and drop in injection pressure when warmed up. Also try opening the gas cap when this happens, if you hear a hiss, or if the problem doesn't happen with a loose cap, the tank vent is plugged up.

 

The current pump is a rebuild from Northland Diesel. Still technically under warranty but i have a hard time beleaving a new pump is the problem. The oil level has not changed. It had a pretty decent oil leak from the previous owner from not doing a good job sealing the housing to the block for the injection pump. I haven't dropped the tanks to look under the bed at the fuel pick ups. Kinda wonder if it would be easier to just lift the bed off to access the tanks.

 

If you have a buddy to help you, I'd remove the bed to service the fuel tanks.

 

never heard of northland, but i have heard many many many horror stories of "rebuilt " injector pumps being worse than the bad ones taken off the trucks

 

This is usually a symptom of an air leak between the fuel tank and the lift pump. Are you in the rust belt? Check your nylon fuel line around the fuel line clamps on the driver side fuel rail. Look for wetness/leaks.

 

You can use a Cherry Picker (Engine Hoist), and 2 straps chris cross the bed corner to corner.
And a third connected under the lip of each wheel arch. Then move truck forward to work on the tanks.

Or buy or build something like this.

I bought one after messing with the straps. Be sure to place a piece of wood under the bed lip to spread out the stress point.
Think I used something like a 1 1/2 x 3" piece.


Charlie

 

Assuming you have 2 tanks does the same issue happen on both tanks, or only one tank? If only one another possibility might be a venting issue on that tank.