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Thread: My CUCV spin on fuel filter mod

  1. #251
    Sergeant CA_LEO's Avatar
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    Thanks @Whitfield for the Duramax filter setup. It made bleeding the system after my banks install an absolute breeze!

  2. #252
    Corporal
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    Hey fuel system peoples!

    I have same problem even after replacing the fuel filter with a custom setup. I am still taking on air and after a day or two after running, it will start right up, for like 5 seconds and then dies. Will not start again unless charged and cranked enough to push the air through, then it starts and runs great, but loses prime again. Now loses prime just overnight.

    So it's not leaking in filter housing anymore (old housing was leaking from water sensor).

    How can I find out if my leak is on the supply line/lift pump side, or the post filter lines to the IP? I am ready to tear out the intake manifold on this and thinking it could also be the line between the lift pump and filter, or even the mech pump has a bad check valve, etc. There are a million ways to lose prime it would seem.

    Can anyone get me a way to prove out which side of the system is leaking or bleeding back to the tank?

    I also am aware of some scary GM tech bulletin saying you need to replace the fuel pump AND housing pressure cold advance assembly on the IP itself must be replaced due to check valve issues allowing fuel to bleed back to and de-prime. This seems extreme to me, as truck runs fine once primed to run.

    Please let me know if you can think of anything? I will probably have to go through all of this and replace it, but how can I test, say, if my mechanical fuel pump is leaking back to the tank?

    or if there is a return line problem? I have been suffering with this for years and thought I had it figured out. Please help.

    Thanks

    Drew
    Newber with the m1028

  3. #253
    Sergeant Major emeralcove's Avatar
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    drewzee87t, my set up is post #236 and nothing that many others have done before me. I had real headaches with losing prime and was determined to solve the problem because I didn't like running the starter so much and getting out over and over to bleed air out of the fuel line every morning. I ordered my filter with a hand primer which I think the Duramax filter has as well. The primer works extremely well and using the starter to bleed air out isn't needed. But after bleeding the air out the first time it never gets used, nice to have though if there ever is an issue and you aren't near civilization when you need to prime the fuel line. I am pretty certain the mechanical pump has a check valve and except for a total PITA to change they aren't expensive. If the diaphragm is leaking and causing the loss of prime you could be leaking diesel fuel into the crankcase which isn't good either. I even experimented to see if I could see if any thing helped and found if it was parked front down hill it didn't lose prime as easy as parked front up hill. Good luck, it is frustrating but once you find the problem, it is hard to remember what a pain it was.
    Last edited by emeralcove; 10-26-2019 at 09:43.

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