Injectors or Fuel pump?
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    Injectors or Fuel pump?

    I've been fighting P0171 and P0174 for a few days now, my tuner has also been noticing that I've been going lean and fuel pressure dropping to about 55 in the upper RPM'S. My LTFT are fairly high once the car is warmed up, about 14-17% while coasting, and if I give it gas they rise to about 21-24% between both banks with RPM. STFT however are fairly decent, always between 0-6%. I cant seem to pin point the issue, no real vacuum leaks either, O2 sensors are working also. I've been wondering if my cruising fuel pressure is OK, it sits at 35-36% at all times when cruising/normal driving. Any ideas and thoughts would be appreciated.

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    There is a test port on the OEM fuel rails where you can hook up a fuel pressure tester to see if your pressure is where it should be or dropping off. They rent them free at the auto parts stores if you don't own one. Its unlikely to be an injector issue when its both sides at the same time.
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    Quote Originally Posted by BlackMarketRacing View Post
    There is a test port on the OEM fuel rails where you can hook up a fuel pressure tester to see if your pressure is where it should be or dropping off. They rent them free at the auto parts stores if you don't own one. Its unlikely to be an injector issue when its both sides at the same time.
    My bigger question is, where is the pressure suppose to be? What's normal pressure on these cars?


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    V2s have a fuel pressure sensor already. You can log it.
    Dedicated Motorsports - Austin, TX
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    Quote Originally Posted by DSteck View Post
    V2s have a fuel pressure sensor already. You can log it.
    That's what I've been doing, I can definitely see the drop at higher rpms, I'm just trying to nail it down it my issue definitely being the pump. So if my fuel pressure is off at cruising then I know that's my issue. I still can't correlate that to the lean condition though, why would it be running lean while driving?


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    It should be at least 55psi with key on, engine off, and not drop more than 5psi or so within a minute.
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    Quote Originally Posted by BlackMarketRacing View Post
    It should be at least 55psi with key on, engine off, and not drop more than 5psi or so within a minute.
    I'll do that in just a few, what about pressure while driving?


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    Quote Originally Posted by BlackMarketRacing View Post
    It should be at least 55psi with key on, engine off, and not drop more than 5psi or so within a minute.
    Attached is a screenshot and log if you don't mind checking it out. Pressure started at 62 and dropped about 8 psi within a minute, could I say my pump is the issue based off of that?
    Attached Thumbnails Attached Thumbnails Injectors or Fuel pump?-fpt.jpg
    Attached Files Attached Files

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    Double check for vacuum leaks. That's the most common cause for your scenario.

    Or the tune is just way off.
    Dedicated Motorsports - Austin, TX
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    Well I think I got that issue sorted out. I am now leaning towards the big issue being my pumps. My file has Desired Pressure Low Flow set at 36 and normal set at 60. I take it low flow is less than optimal for cruising and I should be at 60ish while cruising ? Or am I looking at that wrong?
    Attached Thumbnails Attached Thumbnails Injectors or Fuel pump?-fue-pressure.jpg


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