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Thread: Fuel Pressure questions

  1. #21
    ive done about 15 fpcm deletes between the v's and the 10+ camaros, i agree with dave, all requested and desired pressures revert to the default number once the fpcm is removed, even though the actual pressure reading is zero.
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  2. #22
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    Ok I'm gonna stick with this because I'm such a learning fanatic and I haven't beat my head against the wall on a forum in awhile.

    Ryne, you were SOOOOO close to understanding what I was trying to say. Do me a favor, go back to that tune and switch all the desired fuel pressures to something super low, like 6psi. The part you missed was you need to LOAD THE TUNE IN A CAR AND SEE HOW IT RUNS. THAT'S why I was telling Dave to put 80psi in those settings and DRIVE his car. It will run too lean. The settings DO MATTER DAMMIT! That was my point all along. You need to be aware of this in case it's been changed before you in a tune.

    PLEASE, somebody do my test. Put a low value in those settings, whether the PFCM setting is on "fitted" or "not fitted". PLEASE! Dave, put up or shut up. Put a value 20 psi higher than whatever is in the tune in YOUR CAR and do a WOT run. If you're right, your car will be fine. If I'm right, you'll go too lean and hopefully a blown engine will show you that you need to change your attitude a little bit.

  3. #23
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    Your EQ Ratio or injector settings will also be off if you ignore the "Desired Fuel Pressure" in your tune. Even if you have "FPCM Fitted" set to "NO", it will still reference the desired fuel pressures and they will effect fueling. So if you have 80psi as your desired in the tune and you're only running 60psi with your return system, it will actually run leaner, not richer. The ECM DOES need to know what the desired fuel pressures are, even if it's not able to monitor them. Now that you don't have a FPCM or a fuel pressure input, try setting all the desired fuel pressures to 20psi and see how it runs.

    This was my very first comment on this. If anyone had done what I said instead of instantly attacking, we wouldn't be here right now. Dave, I think YOU need to re-read exactly what I wrote. It IS relevant and it IS correct. Think about this, if you learn this one point I'm trying to get across, guess what? It opens up tuning possibilities! I CHANGE those settings in my tunes either when I have a car with a removed FPCM or when the car still has one. Why? Because it's another way to fine tune mixtures. Have an open mind and you might learn something useful.

  4. #24
    Advanced Tuner jpb1972's Avatar
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    Quote Originally Posted by rynez06 View Post
    once again sorry for the bad iphone pics, my camera is messed up, and this computer doesnt seem to want to screen shot anything.
    notice the actual pressure is 0 even though all others are 75psi....
    LOL. Now im REALLY confused! And why did your FUEL PRESSURE (sae) read "0"?
    And not to change subjects here but why is your commanded AFR 9.35 and your EQ Ratio so low (0.558)? (this could be a noob question)

  5. #25
    like this?? car runs the same... same values.... bro just admit you're wrong. we all make mistakes. we are all here to learn and help one another.
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    Owner of Cunningham Motorsports

    06 z06
    2016 camaro
    68 Camaro
    2014 e63 amg
    07 LBZ Duramax

  6. #26
    fuel pressure is sae 0 because there is no fuel sensor signal. fuel pressure SAE is actual measured fuel pressure. the car is not running during that screenshot. that the cranking fuel values
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  7. #27
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    Quote Originally Posted by DSteck View Post

    On vehicles that use a FPCM, when you delete and go boost references, it doesn't matter where the default pressure is set because proper setup of the injector tables makes it not matter.
    When you guys try what I said, you will see that this statement is 100% untrue. Put a lower value in the default pressure setting in a tune and the car will run richer. Put a higher value in and it will run leaner. It effects the injector rates. The ECM still uses those values whether there physically is a FPCM in the car or not. And whether "fitted" or "not fitted" is selected in the tune. Once you realize that, you can now use those values for tuning.

    Is that what pisses you off so much Dave? Is it that I taught you something you didn't know? When you realize what you said was wrong and what I'm saying is correct and relevant to the OP's questions are you going to be man enough to admit it on here? I doubt it. A member on here asked a question. I added a point that was relevant. You immediately assumed you already knew everything so I must be wrong. The entire thread turns into a mess because you refuse to learn. I'm asking myself why I happened to look on here after being away for months. It's because I know there are guys out there that want to learn and need good information.

    Sorry OP for the derail. I was simply trying to add some relevant info in the thread. If there's anything I can clarify, feel free to ask.

  8. #28
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    I give up. Thanks for keeping me off the forums guys. Later.
    Last edited by gmtech16450yz; 03-26-2015 at 03:07 PM.

  9. #29
    Advanced Tuner jpb1972's Avatar
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    Quote Originally Posted by gmtech16450yz View Post
    This was my very first comment on this. If anyone had done what I said instead of instantly attacking, we wouldn't be here right now. Dave, I think YOU need to re-read exactly what I wrote. It IS relevant and it IS correct. Think about this, if you learn this one point I'm trying to get across, guess what? It opens up tuning possibilities! I CHANGE those settings in my tunes either when I have a car with a removed FPCM or when the car still has one. Why? Because it's another way to fine tune mixtures. Have an open mind and you might learn something useful.
    Dont give up on us! Im sure most can respect what your intentions are here and that is to help others. Even though this makes it harder for a noob like me to decipher what advice to follow and what is the correct way to do things, I appreciate your input.

  10. #30
    Advanced Tuner jpb1972's Avatar
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    Quote Originally Posted by rynez06 View Post
    fuel pressure is sae 0 because there is no fuel sensor signal. fuel pressure SAE is actual measured fuel pressure. the car is not running during that screenshot. that the cranking fuel values
    Gotcha!
    Last edited by jpb1972; 03-28-2015 at 07:17 AM.

  11. #31
    Senior Tuner DSteck's Avatar
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    You don't get it.

    If the FPCM is still present, then yes, changing those values will change behavior. However, I can set those pressures to whatever I want, the FPCM will try to hit those pressures, and the ECM will compensate based on the actual fuel pressure as recorded by the fuel pressure sensor connected to the FPCM (coupled with a calculation of delta pressure based on MAP and modifiers).

    If the FPCM is NOT present, then ALL OF THE INJECTOR CALCULATIONS ARE BASED OFF OF A RAIL PRESSURE EQUAL TO THE DEFAULT PRESSURE, regardless of what the "fitted" switch is set to. For a boost referenced fuel system, if the user enters the injector data the proper way for it (like GM did on 2003 Silverados which are vacuum referenced), then a different delta pressure, be it low or high, is going to have no effect because the IFR will be shown as constant and I changing.

    I can't test on my Z06 because my Z06 never had a FPCM, so it can't be tested on that.

    My CTS-V has a FPCM but is 100% stock, so again, it's not a valid test when this entire thread is based on boost referenced fuel systems.

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  12. #32
    Senior Tuner DSteck's Avatar
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    Quote Originally Posted by gmtech16450yz View Post
    When you guys try what I said, you will see that this statement is 100% untrue. Put a lower value in the default pressure setting in a tune and the car will run richer. Put a higher value in and it will run leaner. It effects the injector rates. The ECM still uses those values whether there physically is a FPCM in the car or not. And whether "fitted" or "not fitted" is selected in the tune. Once you realize that, you can now use those values for tuning.

    Is that what pisses you off so much Dave? Is it that I taught you something you didn't know? When you realize what you said was wrong and what I'm saying is correct and relevant to the OP's questions are you going to be man enough to admit it on here? I doubt it. A member on here asked a question. I added a point that was relevant. You immediately assumed you already knew everything so I must be wrong. The entire thread turns into a mess because you refuse to learn. I'm asking myself why I happened to look on here after being away for months. It's because I know there are guys out there that want to learn and need good information.

    Sorry OP for the derail. I was simply trying to add some relevant info in the thread. If there's anything I can clarify, feel free to ask.
    What pisses me off is your head is so far into that cave that you won't stop to read the thread.

    Boost referenced fuel systems have the IFR set to the same value across the board.
    A default pressure of 18.6psi or 111.4psi won't make a damn bit of difference because both cells will call out the same flow rate.

    Christ. Now I want to actually waste my time calling up a customer to quickly prove this. Let's place a wager on it. What are you comfortable betting? When I win, I will give half of the winnings to a charity of your choice.

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  13. #33
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    Quote Originally Posted by DSteck View Post
    What pisses me off is your head is so far into that cave that you won't stop to read the thread.

    Boost referenced fuel systems have the IFR set to the same value across the board.
    A default pressure of 18.6psi or 111.4psi won't make a damn bit of difference because both cells will call out the same flow rate.

    Christ. Now I want to actually waste my time calling up a customer to quickly prove this. Let's place a wager on it. What are you comfortable betting? When I win, I will give half of the winnings to a charity of your choice.
    You can do whatever you want Dave, I'm outta here. Again, thank you for showing me what a time suck hanging out in forums is. I haven't posted in any forum in months, this was a nice reminder of why. SO many other things or actual people I could have spent this time on.

    I've really tried to help out and share on these forums in the past but it's just not worth my time to argue with guys like you that hang out in internet forums 24/7. (Why the H#LL is it ALWAYS the Vette guys? lol.) I kinda feel sorry for guys that base their whole identity and self worth on how many posts they have on some forum somewhere. I prefer to live my life in the real world with real people that I can touch and feel, but to each his own. I'm sorry I questioned you, I'm an idiot, I don't know anything, I'm wrong about this, I'm wrong about everything I've ever posted and I'll just go back to changing oil in a jiffy lube somewhere. Or in my cave I guess. Your throne is safe, enjoy.

  14. #34
    Senior Tuner DSteck's Avatar
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    You just can't accept that you're wrong and don't fully understand what's being discussed.

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  15. #35
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    I don't have a dog in this fight lol but ya'll have done everything to prove gmtech wrong except for what he has asked or trying to prove change the desired fuel pressure and see what happens to the tune

  16. #36
    Senior Tuner DSteck's Avatar
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    Ryne did.

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  17. #37
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    I am sorry but I don't see where Ryne changed the default fuel pressure in the tune? I am trying to understand all this. Gmtech is saying the default fuel pressure affects the tune and DSteck states in post #31 (ALL OF THE INJECTOR CALCULATIONS ARE BASED OFF OF A RAIL PRESSURE EQUAL TO THE DEFAULT PRESSURE). Does default fuel pressure affect fuel calculation's when fpcm is deleted? Thanks

  18. #38
    Senior Tuner DSteck's Avatar
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    When the FPCM is active, the actual recorded fuel pressure from the sensor is used to calculate delta pressure.

    When the FPCM is eliminated, the ECM uses the default pressure value to calculate delta pressure.

    When the IFR is set to the same value in every cell (as it should for a boost referenced fuel system), the pressure that is used (and consequently the delta pressure that is calculated) won't matter because everything will reference the same numerical value for IFR.

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  19. #39
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    Thanks DSteck

  20. #40
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    I am having trouble with the emissions "fuel system" readiness test on my brothers 2010 supercharged GS with a boost a pump. Could the "desired fuel pressure" tables be causing the continuous test to not set assuming the pressures are higher or lower?(I haven't hooked a FP gauge up to it yet to find out)
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