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Fuel pressure for TBI ?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by husurddy, Aug 8, 2001.

  1. husurddy

    husurddy 1/2 ton status

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    I should start off with a disclaimer about my abilities as a mechanic, I'm not one. I was sent out seven months ago to buy a good family vehicle due to the coming new arrival. I wont tell you my wife’s reaction when I came home with a beat up K5 and a big smile. Before that day I had never even changed my own oil but since then have learned and done a lot. In my quest to find and fix everything on my Blazer I noticed the fuel pressure was at 12.5-13 psi. I have a Holley 670 cfm TBI that, according to the spec sheet Holley sent me, needs 15 psi. My question is will 2-2.5 psi more make a difference and if so, how do I gain this. I should note that I have a new filter and GM ($$$) fuel pump.
     
  2. fr8train

    fr8train 1/2 ton status

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    Try changin your fuel filter. Ummm. I am pretty sure my TBI fuel pump puts out 45 psi.
     
  3. pcorssmit

    pcorssmit 1/2 ton status

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    I've never dealt with the Holley TBIs, I'm assuming you have the one that is a hop-up part that is a direct bolt on, but 15 is a bit too high for a stock TBI, I don't remember the exact range but it sounds like your current pressure is right on. (Also assuming you run the stock TBI, not Pro-Jection).

    Pete

    '83 K5, 350 TBI (ex 6.2), 700R4, NP208, Dana 60/14 bolt, 4.56s, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     
  4. ChevyCaGal

    ChevyCaGal 3/4 ton status

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    I believe 12-14 maybe even 15 psi is correct. I've been looking at pumps to go with the set up HotStuff sold me and that seems to be the info I am getting from parts places...

    C'mon captain break pedal... quit looking for the parade and drive!! [​IMG]
    <a target="_blank" href=http://www.chevycagal.homestead.com/steph.html>www.chevycagal.homestead.com/steph.html</a>
    &lt;&gt;&lt; MARK 1:17 &gt;&lt;&gt;
     
  5. prjt_blzr

    prjt_blzr 1/2 ton status

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    It should be about 15psi for the SBC and about 18PSI for the BBC running TBI. Adding more pressure helps if you are flowing more air. Other than that it just confuses the CPU.
     
  6. newyorkin

    newyorkin 1 ton status

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    13-15 sounds right for the stock pump, unless when you bought it, it was specifically made to push 15+. Do you ever smell fuel anywhere? Possibly a leak, but it would probably be really noticable to cost 2 lbs. Did you use a new screen/pickup with the new pump? If old, maybe the old one's gunked up. Or possibly some kind of restriction in the line somewhere? When you changed the pump, did you find a lot of rust on the sender lines?

    Has performance been affected? I wouldn't sweat it if the truck is running and hauling good.

    Fr8train, I think you might be thinking of TPI or MPFI. My MPFI camaro ran around 35psi, but my TBI K5 runs around 13-15psi (at least my old K5 did with a new pump, haven't measured this one, knock on wood).

    Congrats on the new addition!

    Ratch
    <a target="_blank" href=http://k5.8m.com>k5.8m.com</a>
    **I need a house. Friggin realtor went and sold mine.**
     
  7. husurddy

    husurddy 1/2 ton status

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    The tank is clean, new screen and no obvious leaks. Pressure was tested just forward of new fuel filter. According to my Haynes manual the current PSI is right on for a stock TBI (Not sure of stocks CFM) but less than what Holley is recommending. I think the fuel pressure, to a point, is regulated by the TBI right? If so is there an adjustment that can be made without going to an inline pump?
     
  8. blazer72

    blazer72 1/2 ton status

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    The TBI unit has the regulater in and on older Holley ones its adjusted from the top to the rear with an alen wrench.
     
  9. BurbinOR

    BurbinOR 3/4 ton status

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    Yep, you're right..........TPI runs at apx. 43 psi.

    <font color=blue>'79 ONE TON TPI K5 - See it at---&gt;<a target="_blank" href=http://www.blazzinor.alloffroad.com>www.blazzinor.alloffroad.com</a>
     

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