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420A Fuel Pressure not rising even with FMU...

Posted by cowmilker69, Oct 23, 2018

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  1. cowmilker69

    cowmilker69 Probationary Member

    11
    2
    Joined Mar 13, 2016
    Mississauga, ON, Canada
    Hey yall, I got my boosted 420a here and I have a few questions based on the sh**ty situation I'm in. I'm running a basic, aged 5 psi setup:
    T3/T4 turbo
    FMIC
    12:1 FMU
    255lph walbro
    DSP Electronics FCD

    As of right now the car is running sh**ty. I drove the car with a fuel pressure gauge hooked up and it read a consistent 60 psi. Even under WOT and boost being made, it stayed the same despite that I do indeed have a 12:1 FMU installed. I'm guessing that this FMU I have was faulty from the getgo? What are some common faults with FMUs(i know there are many)? What do I look for to determine what exactly is the problem?

    P.s At first I thought the lean condition was from not having an FCD installed. After installing one the car only got worse. It's normal driving became jerky and now my car is limited to 4000 RPMS. The adjustment screw on the FCD does not seem to do anything. Should I just remove this FCD all togeather?
     

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  2. silvreclips

    silvreclips Proven Member

    786
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    Joined Jul 19, 2005
    Greenville, South Carolina
    Start with the basics and work your way up. If the car is running sh**ty even when you drive easy, don't try to boost it just to see if it gets better. That's how you blow sh** up. Get the car running well first and ease into boost.

    Go over the FMU plumbing and make sure you installed it correctly. You should be getting base fuel pressure at idle and cruising speeds. If your getting 60psi something is wrong and you need to correct that first. Remove the fmu if you have to.
     
  3. cowmilker69

    cowmilker69 Probationary Member

    11
    2
    Joined Mar 13, 2016
    Mississauga, ON, Canada
    The thing is the car was running fairly decent before the FCD was installed. It would occasionally stutter and jerk at cruising speeds and thats why I got the FCD in the first place, but since the day I turboed it the car runs lean under WOT which i'm assuming is because of a malfunction of the FMU somewhere down the line. Btw my car is a 99 and I've seen 99's running perfectly fine with just an FMU, theres video proof on youtube that i'm sure you've already seen.

    All I want is for my car to be able to hit boost properly. As of right now it will build boost and start goin faster but once its WOT and full boost the Air/Fuel ratio dives into lean and the car feels like its slowing down. :(
     
  4. dustyboner

    dustyboner Proven Member

    596
    181
    Joined Mar 13, 2016
    abq, New Mexico
    first check the vacuum line from the FMU to the engine. if the vac. line is okay, take the 6 allen head screws out of the top of it and check the diaphram for damage.

    upload_2018-10-26_5-5-5.png upload_2018-10-26_5-6-29.png

    if its fuct up you can get a new diaphram HERE
     
    1990TSIAWDTALON likes this.
  5. cowmilker69

    cowmilker69 Probationary Member

    11
    2
    Joined Mar 13, 2016
    Mississauga, ON, Canada
    Thank you dustyboner. The link you provided for new diaphragms is from vortech. If I needed a replacement, would those replacement diaphragms still work on my FMU despite it not being a Vortech FMU?
     
  6. dustyboner

    dustyboner Proven Member

    596
    181
    Joined Mar 13, 2016
    abq, New Mexico
    If its a knockoff that looks like the vortech it will work. If its a cartech or synapse fmu it won't.

    Stock fuel pressure is 47-50 psi @ idle. Is your fmu adjustable like the vortech SFMU which allows you to adjust the base fuel pressure?
     
  7. cowmilker69

    cowmilker69 Probationary Member

    11
    2
    Joined Mar 13, 2016
    Mississauga, ON, Canada
    @dustyboner I believe i have the OBX FMU, in which case i dont think it allows you to adjust base fuel pressure. given that, is there any reason why my fuel pressure is always 60 psi? is it because of the FMU? Unfortunately I do not know what the fuel pressure was like before all this turbo stuff...
     
  8. dustyboner

    dustyboner Proven Member

    596
    181
    Joined Mar 13, 2016
    abq, New Mexico
    Unfortunately obx isnt known for quality. The ones i have seen are cheap copys of the vortech FMU.

    I would check that its installed correctly, check the lines, check the internals of the FMU for damage.

    Fuel%20Systems%20wFMU.jpg
     
  9. dustyboner

    dustyboner Proven Member

    596
    181
    Joined Mar 13, 2016
    abq, New Mexico
    is your fuel pump the high pressure version?

    since you have an adjustable FCD, you need to adjust it so it clamps the MAP signal to 4.7v (upper limit).
     
  10. cowmilker69

    cowmilker69 Probationary Member

    11
    2
    Joined Mar 13, 2016
    Mississauga, ON, Canada
    Yes my fuel pump is the high pressure version. I am hoping that is why my idle and cruise fuel pressure is 60 psi.

    As for the FCD, the adjusting pin doesn't seem to actually change anything. Since installation it has limited the car to 4000 RPMs and no matter how much I adjust the pin it does not seem to actually affect anything. I think it's another junk part smh. I have not had the greatest luck with this build but of course it could be worse haha
     
  11. dustyboner

    dustyboner Proven Member

    596
    181
    Joined Mar 13, 2016
    abq, New Mexico
  12. tametalon92

    tametalon92 Proven Member

    1,479
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    Joined Jan 5, 2012
    Rathdrum, Idaho
    Ooooor....megasquirt, add a return line (if needed) and a afpr?



    :D
     
    My DSM:
    1992 Eagle Talon TSi AWD

    Street Build

      manual
    1992 Eagle Talon TSi AWD

    Street Build

    14b   manual
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  13. dustyboner

    dustyboner Proven Member

    596
    181
    Joined Mar 13, 2016
    abq, New Mexico
  14. cowmilker69

    cowmilker69 Probationary Member

    11
    2
    Joined Mar 13, 2016
    Mississauga, ON, Canada
    UPDATE: The problem has been solved. I really appreciate all you guys replying. And yes, I do know megasquirt and larger injectors would be ideal, I'm just not that financially stable if you know what I mean hahaha

    If anyone else has a similar problem with their boosted 420a, my solution lied directly within the FMU. I would watch this video:

    I did exactly the things he did in the video and that solved my problem. That video is like a bible for budget 420a builds. I really think it should be on the home page of the 420a Turbo forum or something.
     
    1990TSIAWDTALON likes this.

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