LLY Won’t stay running anyone have an idea ?

[Squaremax86]

Hey guys I’m new here I’ve been working on an lly duramax that doesn’t stay running it only runs off of prime so I thought there was an air leak on a fuel so I replaced all of the fuel lines and put a fass lift pump on and it still only starts and runs well I’m priming it if I stop priming it dies immediately?‍
Anyone ever deal with this

 

[2004LB7]

Welcome

What's the actual vs desired fuel pressure when it dies?

 

[Squaremax86]

I’m not sure because my fass is pushing 15psi and it still isn’t starting then when I use the priming bulb it has just enough

 

[darkness]

With the lift pump you shouldn’t need to (or even be able to) pump the primer. Check the test port to verify you’re even getting fuel.

 

[darkness]

I’m not sure because my fass is pushing 15psi and it still isn’t starting then when I use the priming bulb it has just enough

15 psi is too high. Back it down to 8-10.

 

[Squaremax86]

I’m not sure because my fass is pushing 15psi and it still isn’t starting then when I use the priming bulb it has just enough

With the lift pump you shouldn’t need to (or even be able to) pump the primer. Check the test port to verify you’re even getting fuel.

I know I shouldn’t need to use my priming bulb after i installed the lift pump I checked the bleeder screw and I have been bleeding air out until it’s just diesel and I have takin the fuel line off after the priming bulb/filter head and I’m getting diesel so I’m very confused .
I was wondering if it was my cp3 pump but well I’m priming it it runs just fine so idk

 

[Squaremax86]

15 psi is too high. Back it down to 8-10.

 

[Squaremax86]

I don’t believe I can adjust it I havent measured how much that’s what I read the lift pump puts out

 

[darkness]

The test port is by the alternator, there’s a schrader valve under the black cap. And do you have a way of checking rail pressure as 2004lb7 suggested?

 

[Squaremax86]

The test port is by the alternator, there’s a schrader valve under the black cap. And do you have a way of checking rail pressure as 2004lb7 suggested?

I don’t have a way to

 

[Chevy1925]

You need some equipment like a food scanner that can read actual and desired rail pressure. You also need to verify you actually are getting fuel pressure at the fuel port and how much pressure its showing. Just because the lift pump is on doesnt mean you hooked it up right or that its actually pushing fuel

 

[Squaremax86]

You need some equipment like a food scanner that can read actual and desired rail pressure. You also need to verify you actually are getting fuel pressure at the fuel port and how much pressure its showing. Just because the lift pump is on doesnt mean you hooked it up right or that its

Yeah that’s a good idea I do know that it’s pushing fuel

 

[2004LB7]

If the lift pump is running, the primer bulb should be hard and difficult to press. If you are able to pump it, it's likely the lift pump is not running

 

[WVRigrat05]

There is a return spring behind the return fitting that you have to change out on the older ones to adjust pressure, I thought the new ones had a adjustment screw like the airdog, either way, pull the feed line off at the motor, shove a smaller hose in it or have someone hold that hose in a bucket and see if it's spraying fuel when you turn on the switch, if not you've got some super plugged filters on the the pump or something else can you hear the pump running?

 

[Squaremax86]

You need some equipment like a food scanner that can read actual and desired rail pressure. You also need to verify you actually are getting fuel pressure at the fuel port and how much pressure its showing. Just because the lift pump is on doesnt mean you hooked it up right or that its actually pushing fuel

I got a friend to bring his scanner and it has 6000psi well I’m priming it and I took my return lines off to test if there is a bad injector returning to much draining the pressure but they are fine and I checked and my lift pump is brand new and it was leaking diesel out of the injector return line so I know the lift pump is working idk what else to check and I have all brand new fuel lines

 

[2004LB7]

I still think there is something funny going on with your lift pump. Does your lift pump run with key at ACC before cranking? If so, is the primer bulb hard?