BeastMaster
Full Access Member
I am of the belief that the IP needs to constantly be supplied with far more fuel than it needs. At a pressure of 6PSI or so.
The excess fuel acts as a coolant for the IP, as it's mounted on the engine and compressing fuel. It should aid in de-airing any incoming bubbles, sending all unused fuel and vapors back to the tank via the fuel return line.
To me, fuel starvation and air intrusion have the same root cause. A blockage.
If it were a hole, you will soon find messy pools of leaked fuel under the truck.
I get the idea the IP is trying it's best to push fuel into the engine, but there's none to give. Fuel pressure at IP inlet zero.
If the IP is forced to pull a vacuum as it tries to suck up a chamberful of fuel to inject, the lift pump obviously doesn't have any fuel ready, the IP will have to suck what it can get from the fuel return line....which is gonna be mostly air.
Now, if you have a hole that air is getting in, you probably have a leak as well - especially if you have an electric lift pump running, fuel lines pressured up, and the engine not running...the IP not taking any.
Edit...
I have thought a bit more on this... if the air intrusion is on the suction side of the lift pump at a high spot...like right on top of the fuel tank, the lift pump will suck air in through it during run, but any liquid fuel run back down during engine off, and not weep out the hole. Then the lift pump will pump foamed fuel. This will likely show up as lots of air accumulating in the fuel filter.
Seems I recall a post by Selahdoor earlier about using a length of clear tubing in the low pressure fuel line so foamed fuel can be quickly seen.
https://www.oilburners.net/threads/vinyl-tubing-and-diesel-fuel.86066/#post-1030879
Given the foam doesn't have enough fuel in it, betcha the air in it ends up coming out in the IP innards and pukes down the fuel return line, again causing low fuel pressure at the IP inlet.
The more I think about this, the more I want to install a fuel pressure gauge at the fuel filter outlet / IP inlet.
You know, I really hate these kinds of problems that wait until I am underway, then they show up. And leave me with yet another guessing game when I am behind the wheel in the middle of traffic. I simply *hate* being the center of attention as the maker of another traffic jam.
The excess fuel acts as a coolant for the IP, as it's mounted on the engine and compressing fuel. It should aid in de-airing any incoming bubbles, sending all unused fuel and vapors back to the tank via the fuel return line.
To me, fuel starvation and air intrusion have the same root cause. A blockage.
If it were a hole, you will soon find messy pools of leaked fuel under the truck.
I get the idea the IP is trying it's best to push fuel into the engine, but there's none to give. Fuel pressure at IP inlet zero.
If the IP is forced to pull a vacuum as it tries to suck up a chamberful of fuel to inject, the lift pump obviously doesn't have any fuel ready, the IP will have to suck what it can get from the fuel return line....which is gonna be mostly air.
Now, if you have a hole that air is getting in, you probably have a leak as well - especially if you have an electric lift pump running, fuel lines pressured up, and the engine not running...the IP not taking any.
Edit...
I have thought a bit more on this... if the air intrusion is on the suction side of the lift pump at a high spot...like right on top of the fuel tank, the lift pump will suck air in through it during run, but any liquid fuel run back down during engine off, and not weep out the hole. Then the lift pump will pump foamed fuel. This will likely show up as lots of air accumulating in the fuel filter.
Seems I recall a post by Selahdoor earlier about using a length of clear tubing in the low pressure fuel line so foamed fuel can be quickly seen.
https://www.oilburners.net/threads/vinyl-tubing-and-diesel-fuel.86066/#post-1030879
Given the foam doesn't have enough fuel in it, betcha the air in it ends up coming out in the IP innards and pukes down the fuel return line, again causing low fuel pressure at the IP inlet.
The more I think about this, the more I want to install a fuel pressure gauge at the fuel filter outlet / IP inlet.
You know, I really hate these kinds of problems that wait until I am underway, then they show up. And leave me with yet another guessing game when I am behind the wheel in the middle of traffic. I simply *hate* being the center of attention as the maker of another traffic jam.
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