isx will not start cranking low fuel pressure

[ktbtrucking]

Hello all,

the issue I have is as follows ... truck have stalled and towed it to repair shop.
They have changed fuel filter so far truck cranks but no start. Have arrived today to the truck have an active code for low fuel pressure. connected insite is shows 16psi with key turned on it goes to 68psi when cranking and book says should be at least 100psi.
Have tried use some fluid starter it starts for a sec and stalls. I assume I have two low pressure builded. Might have clogged fuel lines. Do not see any fuel leaks at prime pump but assume it might sucks air. Any thoughts what to do next.

[preacherboy24]

I believe you need a new fuel pump. They will just "go out" all of a sudden. I know a guy who had the exact problem you have. His psi was 70 when he was cranking the engine over and you are at 68. The pressure should be over 100psi. He changed out the fuel pump and all is well.

[ktbtrucking]

thank you
you mean ISX fuel module with gear pump and accuators or just a lift pump?

[Rawze]

My CM871 is over 130 PSI while cranking. 70 PSI sounds too low. will likely have issues crank up and run. i think I read somewhere minimum is 50 psi, but it should be 100+ if it is healthy. Sounds like you have a bad gear pump, but then again, you never mentioned what model ISX it is.

[preacherboy24]

(10-09-2016 )ktbtrucking Wrote:  thank you
you mean ISX fuel module with gear pump and accuators or just a lift pump?

Not the lift pump. There is a gear driven fuel pump that runs off the cam. The IFSM is the whole unit the fuel pump bolts to. Just replace that. Should be around $450

[ktbtrucking]

it is 2002 non egr isx500hp i believe it is a model before cm870 , but fuel module looks the same if I remember it right, will ask the dealer about gear pump and let you know thank you

[preacherboy24]

Its on top.....over the top of the actuators. It unbolts.

[ktbtrucking]

repair shop separated some fuel lines to double check if it is the high pressure pump for sure, put outside pressure gauge and did some tests, they claims it is lift pump , maybe it has not enough flow to create 100psi will see, they are going to change lift pump, will let you know afterwards

[preacherboy24]

I hope that is it but I doubt it. The guy I know did the lift pump first and it wasnt the problem.