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TBI Fuel Pump Pressure?

Discussion in 'The Garage' started by wkasak, Jan 30, 2006.

  1. wkasak

    wkasak Registered Member Premium Member

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    **Update - 02/10/06**
    I have verified that TBI's do not hold pressure without the engine running...they have a built in relief valve.
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    I have been testing my fuel pump for possible failure...can anyone tell me if the following is normal or abnormal?

    When I turn the ignition on the fuel pump runs for about two seconds and builds pressure to about 12-13 psi...immediately after the pump stops the pressure drops to 0 in about a 1-2 seconds. This all happens without actually starting the engine. I do not believe this is normal and suspect the pump check valve is defective. Shouldn't the pressure hold after the pump stops? Can anyone verify I am on the right track? What else would cause this if it is not normal?

    Thanks in Advance...
     
    Last edited: Feb 10, 2006
  2. neverendingproject

    neverendingproject 1/2 ton status

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    That's what mine does. It will purge the system, and even though there is not pressure, fuel is there for starting in which case the pump comes on again. 13 psi is, in all reality a good pressure to have for a stock motor, if yours is stock, Id say there is nothing wrong with the pump
     
  3. opfor2

    opfor2 1/2 ton status

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    Remember that the fuel pressure regulator is doing it's job. any fuel not used by the injectors is returned to the fuel tank via the return fuel line. so in other words the fuel is making a big loop tank to TBI and back to tank. The pressure drop is normal
     
  4. K5er4Life

    K5er4Life 1/2 ton status

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    Are you having any abnormal problems? Particularly when starting? Or just trying to find something wrong so you have an excuse to get away from the old lady for a little bit? j/k but the sounds pretty normal to me.
     
  5. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    That's normal.
     
  6. wkasak

    wkasak Registered Member Premium Member

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    There are two "issues" that have me looking at things:

    If I crank the engine it takes 4-5 cycles before the engine will fire. However, if I crank it 1-2 times then turn the ignition off...I can just tap the ignition again and the engine will fire immediately.

    I have an idle surge that has been bugging me for a long time. When warm at idle the engine idle will drop down to 400-500 rpm then the computer will automatically adjust and the rpm's will go up to about 1000-1200 rpm. Then repeats over and over.

    So for these two issues I have been testing individual pieces of the system to isolate the problem. All of the TBI/Fuel Injection reading I have been doing says the pressure should hold after the pump stops running? I also suspected that it was normal that it would bleed off...just wanted to verify...

    I should also include that it is a high volume pump used to feed the Whipple Supercharger. I have a new custom ECM chip ordered to see if that changes anything too (currently Whipple chip installed). I am beginning to think these are just common issues of forced induction...although Whipple techs tell me that it should idle and start like stock.
     
  7. K5er4Life

    K5er4Life 1/2 ton status

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    Theres your problem right there. Its going to take a little bit of work to fine tune that tbi system, they dont take aftermarket mods very well without a bit of work to the prom. What does those guys say about how much pressure your running through the system, on a stock application that pressure is perfect but with higher performance mods, specially with a charger I think you want a higher pressure feeding the system. To begin with atleast tahts something to think about. On my 383, which is not built that big at all (torqer heads, 2.02/1.60 valves, holley intake, holley tbi, full roller motor, the cam is mild) and I have surging issues until I am slowly starting to get the computer to better understand these modifications better. Also my pump is supplying, from what I can remember, around 38 psi at idle. What year is your tbi setup, cause you want to pay attention to the size injectors you have flowin. Going to need more details to understand what you got goin on better. But in the mean time check out www.thirdgen.org and www.turbocity.com If you havent already these guys know there stuff when it comes to modifying the oem tbi equipment.
     
  8. wkasak

    wkasak Registered Member Premium Member

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    It's a 1989 K5 TBI System with stock fuel injectors. I am looking at trying to replace those also to see if it helps. I have already replaced and/or tested the EGR, MAP, TPS, IAC, and had the throttle body sent out for blueprinting.
     
  9. 79k20350

    79k20350 3/4 ton status

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    i thought the fuel system was supposed to hold pressure?:confused: i know with my lt1 it would hold 40psi for over a half an hour, and would have pressusre first thing in the morining (prolly around 10) as far as i knew injection systems were supposed to hold pressure and if it bled off quickly it meant the regulator was bad. maybe tbi is differant but i know that this is true with multiport. this may be why its hard to start, theres no pressure on the injectors. also the cranking it 1-2 times and then stopping then doing it again could be the pump building pressure and thats why it fires the next time. call me crazy but it sounds like a bad regulator. then again im no tbi expert. :o multiport on the otherhand, ask away:D as for the surging, im not really sure:o
     
  10. wkasak

    wkasak Registered Member Premium Member

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    Whipple tech support just told me that it should hold pressure...Should I believe them?
     
  11. 79k20350

    79k20350 3/4 ton status

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    yeah i would. everything ive been told about fuel injection is that it should hold pressure. i would replace the regulator.
     

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