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Thread: LT4 HPFP dropping then coming back up

  1. #1
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    LT4 HPFP dropping psi but recovers with rpm?

    Hey guys needing a little help. Car is a 2014 C7 Z51, LT4 Hpfp/injectors, Gsl392 kicking on at 4 psi for low side tee in just like dsx, D1SC 13psi, Alky 10+15 nozzle, msd intake, stock cam. Car made 769 on 62% E and it was a 95* day. High pressure held solid at 2900. Now its getting cooler 60-70 out and I believe making more boost and the hpfp cant keep up. I dropped all the way down to 42% E and its still dropping down to 2400ish but then high side recovers with more rpm? Which is really throwing me off? I've attached 2 pulls and my tune. Any help is appreciated. Also just fyi I have tried a GM LT4 hpfp and a brand new out of the box AC Delco Lt4 Hpfp and both do the same thing.
    Attached Files Attached Files
    Last edited by devin.918; 4 Weeks Ago at 06:36 PM.

  2. #2
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    I'm still a tuning noob, but you're out of high pressure fuel pump with the stock cam at that level IMO. An aftermarket cam with a +32 fuel lobe would take care of that I suspect. You could try E30 and see if that helps in the meantime?

  3. #3
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    I think so too, it gets better the lower E content I have. But what completely throws me off is the pressure coming back up? Am I that close to the edge that the higher rpm is driving the pump just enough to bring it back up? That's the only thing I can come up with.
    Last edited by devin.918; 4 Weeks Ago at 09:18 PM.

  4. #4
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    You're at the limit of the high side. Bring it down to E30 like suggested above or spray more meth to supplement, but I don't suggest that.
    2019 C7 ZO6 M7.

  5. #5
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    Thank you. Have you ever seen high side pressure return like that with Rpms before though?

  6. #6
    Quote Originally Posted by devin.918 View Post
    Thank you. Have you ever seen high side pressure return like that with Rpms before though?
    Yes, the high side pump is mechanical so the faster you spin the engine (more specifically the cam shaft) the more the pump can flow.

  7. #7
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    Awesome, thanks for all the input guys. That was the only thing I could come up with as well.

  8. #8
    What's you injector pulsewidth? Anything over 5.6-5.7 is too much.

  9. #9
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    Quote Originally Posted by 32vape View Post
    What's you injector pulsewidth? Anything over 5.6-5.7 is too much.
    When pressure is good 5.5 but when it drops 6-6.5 depending on how low hpfp falls off.