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Thread: TBI guys: What fuel pressure you running?

  1. #1
    The Baby Seal Says: drewdaddyblazin's Avatar
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    TBI guys: What fuel pressure you running?

    Well its almost spring time which means the track will be open. Now that I have enough money to build a new rear I want to make my engine completely tuned... Ive been playing with the fuel pressure this weekend, I put it up to 15psi and took it out for a drive... Seems its not enough.. Im not getting a misfire anymore but it still bogs down at about 3700rpms, then i let off obviously. So i put it in park and reved the motor up watching my 02 monitor. It gets about 2 bars at about 3000rpms and zero bars at 3700-4000. So that tells me its still too lean... Every motor is different, but whats a good general pressure to shoot for with a motor like this:
    10:1 compression
    272HR comp cam (.500 gross lift, 215 @ 50 both intake and exhuast)
    68phr police TBI injectors
    675 CFM holley
    Edelbrock TBI intake
    stock 193 heads with angle grinded valves/port work

    I dont have the stock TBI pump, its a 96 blazer pump for a 4.3. Ive read that those are capable of 30psi? If i feel like it today Ill probably bump it up even more to 17 and see how that works...
    (08:25:41 PM) AndySeals355: shes one of those jesus loves everyone types lol
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  2. #2
    Let's Go Pens! S/T Lover's Avatar
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    Are you sure you aren't running too MUCH pressure? I've never heard of anyone running above 14psi on a tbi unit. I know for a fact the stock requirements is between 8 and 12.


    Also, junk that holley tbi. Get a TBI from a 454 engine. Those holleys are pieces of shit.
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    In 1095, Pope Urban II commanded the beginning of the most heinous period ever documented: The Crusades. While killing over 100,000 Turks in 1098, the Christians "did no other harm to the women found in [the enemy's] tents - save that they ran their lances through their bellies," according to Christian chronicler Fulcher of Chartres.

  3. #3
    Senior Member 00Blazer's Avatar
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    Originally posted by S/T Lover
    Are you sure you aren't running too MUCH pressure? I've never heard of anyone running above 14psi on a tbi unit. I know for a fact the stock requirements is between 8 and 12.


    Also, junk that holley tbi. Get a TBI from a 454 engine. Those holleys are pieces of shit.
    im with him on the pressure, your probably running it too rich. Also where is your air fuel sensor mounted in the exhaust?

  4. #4
    The Baby Seal Says: drewdaddyblazin's Avatar
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    its on the drivers side Y pipe... 8-12psi? According to cfm-tech.com 13-15 is good for stock motors. Maybe they dont know wtf they are talking about because my motor doesnt seem to like that obviously! Im really close to running outside real quick and changing it...

    Also, i know youre right on one thing 00... That holley unit IS a piece of shit! The throttle blade return spring isnt enough to close the blades at idle... Im like uh lol.. So i replaced it with another spring.. The injectors died on me too, luckly i was able to put the GM pod on the holley.

    Anyways, im going to go fuck with my truck... Ill set it at 10 JUST to see what happens..
    (08:25:41 PM) AndySeals355: shes one of those jesus loves everyone types lol
    (08:25:42 PM) Zachary188: when she's ontop you'll have the cross necklace hitting you in the face!
    (08:25:49 PM) AndySeals355: LMFAO

  5. #5
    Senior Member 00Blazer's Avatar
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    http://www.cfm-tech.com/gm_tbi_fuel_pressure.htm


    read the entire page. also another problem is the holley doesnt support over 275 hp.




    Last edited by 00Blazer; 02-18-2007 at 09:11 PM.

  6. #6
    Zombie Killer 6SpeedBlazer's Avatar
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    tbi injectors dont shut down till 45 psi, so i dont think he is running to much pressure

  7. #7
    Let's Go Pens! S/T Lover's Avatar
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    Originally posted by drewdaddyblazin
    its on the drivers side Y pipe... 8-12psi? According to cfm-tech.com 13-15 is good for stock motors. Maybe they dont know wtf they are talking about because my motor doesnt seem to like that obviously! Im really close to running outside real quick and changing it...

    Also, i know youre right on one thing 00... That holley unit IS a piece of shit! The throttle blade return spring isnt enough to close the blades at idle... Im like uh lol.. So i replaced it with another spring.. The injectors died on me too, luckly i was able to put the GM pod on the holley.


    Injectors died on mine as well. Almost stranded my ass at Carlisle. It sucked.

    I'd definitely go to a 454TBI if you can find them. Also, in that article that 00 posted, it looks like it might be time for a computer reprogram since you are adding fuel pressure but it isn't making and difference.


    I thought I read somewhere that too much pressure can, at times, cause the same problems as too little pressure, but I may be mistaken. Anyways, I think that a computer reprogram is going to certainly be needed for reliability and trust in the system.
    LT1/4L60E/Shaved handles, emblems, antenna/5-4 Drop/16" Xtreme Wheels.


    In 1095, Pope Urban II commanded the beginning of the most heinous period ever documented: The Crusades. While killing over 100,000 Turks in 1098, the Christians "did no other harm to the women found in [the enemy's] tents - save that they ran their lances through their bellies," according to Christian chronicler Fulcher of Chartres.

  8. #8
    The Baby Seal Says: drewdaddyblazin's Avatar
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    oh i got a custom programmed chip from TBIchips.com... I have the pressure set at about 12... It actually pulled harder than having it at 15psi... Im going to have to josh around with this some more...
    I also read that my MAP sensor has to be oreiented in a certain direction for the sensor to read properly. That is, with the vac hose pointing down. Maybe thats where Im getting the increased power...
    Also, i was listening closely to the motor when i was running it hard. I swear i hear a vaccum leak... When i get back from class tomorrow im going to get the soapy water out... If there is a leak, that could be my problem...
    (08:25:41 PM) AndySeals355: shes one of those jesus loves everyone types lol
    (08:25:42 PM) Zachary188: when she's ontop you'll have the cross necklace hitting you in the face!
    (08:25:49 PM) AndySeals355: LMFAO

  9. #9
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    Whats the lobe seperation on your camshaft?
    may want to check with Brian @: http://www.tbichips.com/
    email him your combo.

  10. #10
    Your mom's box! slammins15's Avatar
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    You may also want to do a search on fullsizechevy.com lots of info there about TBI stuff plus lots of complaints about chips from tbi chips
    I'm a black ninja motherfucker!



  11. #11
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    hey, for that engine you shouldnt have to boost it up to 15, changing it isnt going to do anything really, its your tune. The only time you need to boost your fuel pressure is when your injectors are almost static.......


    Mine is backed way off and im running 10:1 almost in open loop because the chip i got burned was made with my dataloggs with a worn out fuel pump.... so theres way more fuel avaiable than what your eninge needs.


    89' S10 blazer 4wd: 355, 650 dp, rpm intake, comp 282 roller cam, modified vortecs, T56 Six speed, 8.8 ls rear, headers, x-pipe, spintech pro street mufflers, and......AC

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  12. #12
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    btw, you ever put a fuel gauge on and watched it under wot past 3700rpm?


    89' S10 blazer 4wd: 355, 650 dp, rpm intake, comp 282 roller cam, modified vortecs, T56 Six speed, 8.8 ls rear, headers, x-pipe, spintech pro street mufflers, and......AC

    Blazer burnout video - http://www.youtube.com/watch?v=sP7iLypoDI4

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