krawler-N-tow

My truck is not holding fuel pressure after the truck is cut off. I have to bump the starter to get the Air Dog pumping, wait until it stops(16psi) then it takes me about three tries to get it started.This started not long after I reinstalled a set of 75hp injectors.
This truck sits, alot. I've only started it twice in the past 2.5wks. Both times it initially had zero fuel pressure. The leakdown is happening in a matter of minutes. I've tried researching this and found that it could be a leak in the stock return line but I can't find diesel anywhere?

KATOOM

You probably have one or more cracked injector line o-rings from changing the injectors.

krawler-N-tow

I'm not finding evidence of a fuel leak in the oil or anywhere on the truck
Has anyone ever come across a problem with an AirDog like this?

rickf

It sounds like you are losing prime, none of the trucks hold pressure when turned off. If I had to guess I would say a leak in the line between the pump and the tank is allowing the fuel to run back to the tank and get air in the line.

Rick

KATOOM

The injector o-ring has nothing to do with fuel getting in the oil. But.....lets look at this from another point. Has it been very long since you installed the Airdog? How old is the VP? And also, fuel pressure bleed down will take place immediately after you shut the truck off. Thats normal. But in saying that, you dont want to loose the prime in the fuel lines either. A leak of any sort will allow air to enter the fuel system and cause the fuel in the lines to drain back to the fuel tank. The best and easiest way to determine if you have a leak is to park the truck overnight with the nose pointed downhill. What that does is bring the tank up so that gravity is less likely to allow fuel to drain out of the lines. If it starts fine parking like that then you have a leak but if it doesnt help then you're Airdog may be over-pressurizing the VP during engine cranking. The way to determine if thats the case is to pull Airdog fuse and see if it starts normal. If it does then makes sure that fuse is put back ASAP.

Dieseldude4x4

My FASS has become increasingly noisy over the past several months (I can hear it over my stacks) and I noticed it takes longer to build up fuel pressure as well. I pulled the FASS off this week and the suction line between the pump and the tank was bone dry. The return line to the tank and the line to the injector pump were full of fuel. This indicates to me that the suction line could be letting air in and losing the prime. The two steel lines going into the tank are very rusty too. I have ordered the new 5/8 inch suction line kit from KLM which will eliminate the restriction in the suction line. Gotta drop the tank and drill a new hole for the new kit. Ask me in about two weeks how it works.

maxwellp

"And also, fuel pressure bleed down will take place immediately after you shut the truck off."

Mine does this also - but it starts every time. If you bump the key it should run the fuel pump for 25 sec or so. Mine will come right up to 16 psi if I do that. I think you have some other problem.

j-fox

My 95 and this 02 both had leaks in the return line that made them hard to start after sitting. Neither truck had a diesel leak but allowed air into the return lines!!!
Air can leak where a fluid cannot.

Dieseldude4x4

Mine use to build up just bumping the key but now it has to be running. I tested the FASS off the truck and it does fine there.

nitrousn

Thats exactly the truth. Most people are to lazy to look for the problem.

rickf

I do not understand how a leak in a return line can cause hard starting. A return line leak will just allow the fuel to return to the tank just as it would normally. There is no way for the air to get to the suction side of the pump from there. What am I missing?

Rick

maxwellp

I will join Rick, I don't get it. There is a check valve at VP44, if this was bad it could make problems. But if all the fuel drained after this it would not matter. IMO

KATOOM

First off, the VP has NO check valve. Its called an overflow valve and it has nothing to do with making sure fuel doesn't escape the VP. Matter of fact, it has a hole in it too.
The reason a leak of any sort will cause hard starts is because the fuel system requires that it maintains a prime.....not maintain pressure. Thus that means that all the fuel lines must stay full of fuel. An air leak will allow the fuel to drain out of the fuel line just like holding your finger over a drink straw and removing the straw from the cup. When you take your finger off the straw or if the straw has a crack in it then the water will drain back in the cup. Does that help?

maxwellp

Ok, I have now seen the little hole in the overflow valve. So a small air leak will also pull all or most of the fuel out the the vp44?

KATOOM

Couldnt tell you if its actually "pulling" fuel out of the VP but apparently the VP requires that there is no air gap within the entire fuel system otherwise the fuel pump then must pre-prime the system which is the extended cranking hard start after then engines been sitting for awhile, like overnight.