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TBI tuning problems

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Jonny-K5, Aug 28, 2005.

  1. Jonny-K5

    Jonny-K5 1/2 ton status

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    just finished up installing all my CFMtech goodies. i put the TBI spacer, injector spacer,adj. regulator and gauge on. my problem is the fuel pressure. according to the website tech, i should have it between 13.5-14.25 psi. if i set it in that range,and drive around the block, the pressure drops. usually by about 1lb. enuf that its below the 13mark. has anyone else had this problem? also seems like its cutting out above 3000rpm.
     
  2. 4xcrazy

    4xcrazy 3/4 ton status

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    13-14psi?

    i could have sworn that my STOCK unit was running at around 20-25psi or so, i know my TPI on my Camaro was running at 45psi.

    something different with your setup? as to why it would need less pressure? just seems too weak to me for some reason. :dunno:
     
  3. smokkey1

    smokkey1 1/2 ton status

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    when you get it dialed in let us know. I want to get the same goodies and a new exhaust + headers soon.
     
  4. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    TBI is a low pressure system utilizing between 9-15 psi with optimum around 13.5 psi. TPI is a high pressure system utilizing between 40-50 psi and depending on your mods usually somewhere around 44-45 psi optimum.
     
  5. Jonny-K5

    Jonny-K5 1/2 ton status

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    i fixed the cutting out above 3k, i didnt have the TV cable dialed in correctly.
    when i started my truck this morning, the needle on the PSI gauge pegged. so it was somewhere above 15 since thats as high as the gauge goes. dialed it back to about 14 psi and drove to work. when i get to work i pop the hood and its around 11.5. for some reason when it heats up its losing pressure. i've got no leaks anywhere that i can see. what would causs this? no one else with the adj regulator has noticed this?
     
  6. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Sounds to me like a bad pressure regulator.
     
  7. Jonny-K5

    Jonny-K5 1/2 ton status

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    i think you might be right, probly faulty diaphram. :thinking:
     
  8. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    Check your pressure with a decent gauge. I have a summit racing one plumbed into my fuel line and it reads what the heck it feels like! usually between 7 and 12 psi! I put a Snap On gauge on there to test it and it was 18 lbs. I set it up with the Snap On gauge and it runs great. The Summit gauge is still all over the place!
     
  9. neverendingproject

    neverendingproject 1/2 ton status

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    It could be due to your spring in your FPR and the fact that as it heats up and cools down, the qualities of the spring change much like oil does when its cold vs when its hot. If you get the problem fixed let me know as i am doing my own tbi swap with higher fuel pressure.
     
  10. BigCountryx

    BigCountryx 1/2 ton status

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    just digging up an old thread instead of starting a new one. Did you ever get the fluxuating ppressure problem figured out? Are you happy with the results, what would you change? I'm about to install the same thing and would rather just set it and forget it, if you know what I mean.:D
     
  11. camok5

    camok5 1/2 ton status Premium Member

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    I second this because I have the exact same problem with my fuel pressure jumping from pegging the needle to 11 psi? I also have the same set up from cfm-tech.
     
  12. Jonny-K5

    Jonny-K5 1/2 ton status

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    never got it to stabilize.i just figured the gauge was off when the engine temps went up like someone mentioned. i set it to 14psi when cold and stopped looking at it.

    i still have a problem with the engine running rough/rich at cold startup. i think i might try removing the TBI spacer. good luck. let us know if yours fluctuates too.
     
  13. Thunder

    Thunder 3/4 ton status

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    Your engine is running rich because of the higher fuel pressure.When cold in open loop ECM doesent know the pressure is up. The pulse width is still the same as when the pressure was lower. So more fuel is being added in open loop. Its a trade off you have to put up with with a manually adjustable FPR. If the idle is really a problem you can go with a vaccum referenced FPR which drops the FP down to around 10PSI at idle and cruise and boosts up to 15+ at WOT
     
  14. mouse

    mouse 1/2 ton status

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    Does anyone have a recommended fuel pressure gauge? It sounds like the Summit gauge is not a very good one.
     
  15. Jonny-K5

    Jonny-K5 1/2 ton status

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    who sells these? ive looked around and havent seen any.
     
  16. Thunder

    Thunder 3/4 ton status

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    You can get those vaccum referenced regulators from your local Chevy/ GM parts dealer. GM TBI regulator P/N 17113186. GM used them in BBC Marine engines and some BBC vehicles. They will work fine on a 350
     
  17. mouse

    mouse 1/2 ton status

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    Any idea on the price of a vacuum referencing fuel pressure regulator?
     

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