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Thread: TBI Adjustable Pressure Mod

  1. #1
    Fuel Injected! mudbuggy's Avatar
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    TBI Adjustable Pressure Mod

    Hi. All. I got a spare tbi from my local pullapart this spring, then this summer got the gasket set for this unit, I was going to rebuild the spare then swap out for the original after I got my pressure gauge installed. Which I finished this past weekend. I installed the gauge for. Reasons. First my youngest daughter (seven years old of 6 kids) likes to work on my truck with me, I am suspecting that the fuel pump is original, next I wanted to known what the pressure was and lastly,for a baseline of when I start to bolt on mods. Which by the way I'm at 9.5 psi and I also double checked the electric gauge with a mechanical. My next purchase will either be the cfmtech spacer or the aldl cable, right now I am thinking the cable so I can see any changes in system then the three wire O2 sensor then the O2 tuner setup. I really am trying to avoid doing any mods that change it from the oem setup until I habe all of the sensory equipment need to read all mods in the future


    So with the background out of the way I have a few stupid questions about thbe was and lastly,for a baseline of when I start to bolt on mods. Which by the way I'm at 9.5 psi and I also double checked the electric gauge with a mechanical. My next purchase will either be the cfmtech spacer or the aldl cable, right now I am thinking the cable so I can see any changes in system then the three wire O2 sensor then the O2 tuner setup. I really am trying to avoid doing any mods that change it from the oem setup until I have all of the sensory equipment need to read all mods in the future


    So with the background out of the way I have a few stupid questions about the pressure regulator. How does the adjustment stem get changed? Does it stick through the base, if so what happens to the vacuum port on?

    Thanks,
    1989 GMC V1500
    2002 Chevy Trailblazer
    1988 Dodge Ramcharger

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    RIP EagleMark's Avatar
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    Re: TBI Adjustable Pressure Mod

    I think you have a TBI conversion on something? Vehicle, motor and information would help.

    Making a stock TBI regulater isn't hard. Here's an article from ThirdGen.org
    http://www.thirdgen.org/tbi-afpr

    But a stock regulater will usually run 13 PSI. I have yet to see one stock that does not with proper fuel pump, lines, clean filter, enough electrical power, big enough wires from relay power good grounding to frame, frame to motor, motor to body. Yours at 9.5 PSI is very low. I'm not sure a adjustable regulater is going to help, I think you have another issue.

    If you have not rebuilt your TBI then that would not hurt and you would have it apart to do the Mod. Get the injectors serviced while out!

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  3. #3
    Fuel Injected! mudbuggy's Avatar
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    Re: TBI Adjustable Pressure Mod

    OK now that I'm home I can use the laptop, not the pda, a lot easier. I am rebuilding another tbi unit and I am installing the adjustable fuel regulator on it. That way I know that everything is up to oem specs or above once I bolt it on. Everything will be done on the rebuilt one not just a clean up and regasket, why do half the job when its apart it a lot easier to do all of it and there is less to worry about down the road.

    Once I got the pressure guages installed I checked the relay for power there, it was .6 volts off of the battery, I don't want to cut, or 'scrape' a wire going back to the fuel pump just to get a power reading. I'm sure that in the next year, hopefully longer but Murphy has a thing for me, I'll be changing the fuel pump. At that time I'll do something that will make it easier to test connections and/or change out the wiring to the fuel pump, just because it's 25 years old and there's salt used here for the snow. When I do the fuel pump I am also going to add the shackle flip when I have the tank out, and cut a hole in the floor (clean and with a fabricated cover that fits tight) so I don't have to drop the tank for a fuel pump swap or even to change out the sending unit all together.

    The fuel filter was changed when I installed the sending unit for the electric guage this weekend. I made a hydraulic line with the fittings that I needed to just hook into the fuel system between the filter and the tbi so I know that the filter is beginning to get clogged, or whatever. At first I thought that I would leave the old filter on, then I figured that I would change it out that way I don't have to crawl under the truck twice. So I did.

    I did notice on the original tbi unit that the tab in the fuel regulator bowl is bottomed out. That is its the furthest away from the hood. I figure it was just set low from the factory, but you guys are the pros at this stuff, I'm learning.

    The original reason I began to post here was that I have seen some of the fuel regulator setup in the past that have an adjustment that is inside the spring housing, and it is adjusted by removing the housing off of the tbi unit turning the set screw then bolting it back on and checking pressure, if it not right then rinse and repeat. Others I have seen (this is where I am having my question) have an adjustment screw that protrudes out the bottom of the 'can' it also drilled thru the tbi base. What happens to the vacuum source on the back of the tbi base? Is it just capped off is it ported or what? I am assuming that what ever is hooked up to that port, then I just relocate to another vacuum port?
    1989 GMC V1500
    2002 Chevy Trailblazer
    1988 Dodge Ramcharger

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    RIP EagleMark's Avatar
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    Re: TBI Adjustable Pressure Mod

    Don't worry about a vacuum adjustable regulator unless you have built a big HP engine and are running lean top end. They are very hard to tune. Just do the mechanical adjustable regulater.

    .6 volt loss at relay is not bad. loss at pump would be better reading, with you mentioning slted roads a ground issue is likely.

    If you make the regulator adjustable, first don't drill the plug to far, you can easily take out the head of threaded bolt in there. When you get it out and slot it of find an allen to put in. When you get the injectors back in and the injector pod is done, don't put it on TBI. Hook it up to fuel lines and turn on key and watch pressure, you get 2 seconds. Then adjust, then 2 seconds, then adjust till 13 PSI. Then reinstall on TBI and try it out.

    I just looked at three here in my shop and none of the tabs in regulator are bottomed out?

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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    Re: TBI Adjustable Pressure Mod

    A much easyer way to adjust the fuel pressure is to just grab the knob with plires and turn.
    See here:
    http://www.binderplanet.com/forums/show ... post298293
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

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  6. #6
    Fuel Injected! mudbuggy's Avatar
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    Re: TBI Adjustable Pressure Mod

    JeepsAndGuns
    That's a lot easier then tearing it all down and rebuilding it. I'll look at mine in the shop tomorrow and mighj tinker with it after I get the bills paid for the day.

    EagleMark
    In the picture below I have seen other modified tbi units with the adjuster going from the can through the tbi base and exiting the bottom of the tbi about were the vacuum line is at. Isn't that for a sensor? Is that a pressed in fitting? I have mine apart and I am looking for the correct bolt to use for the adjuster screw. I guess I could use a allen flat tapered head screw leave it inside of the can. But the adjusters that stick out of the bottom really make me wonder, I'm really interested in that, since my fuel lines are steel lines up top, if I would attempt to set and adjust I would only make a mess of things with fuel spraying all over.

    I can only imagine how cautious I will be when I get the cable and then need to solder, I'm nervous just thinking about it. Not really, but a heat gun isn't a torch!
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    1989 GMC V1500
    2002 Chevy Trailblazer
    1988 Dodge Ramcharger

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    RIP EagleMark's Avatar
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    Re: TBI Adjustable Pressure Mod

    Fuel does not spray when key is turned on for prime. Only when you hit crank. I always set up adjustable regulaters this way.

    That vacuum line in picture is for MAP. I have seen people T into it with vacuum for fuel pressure regulater but I would find somewhere else. Don't like to mess with vacuum to the most important sensor of system. Somewhere on here is a picture of one a guy drilled through the throttle body down to I guess the IAC vacuum port, brazed in a vacuum fitting and ran an elbow to the line he drilled in. Most TBI units have a direct vacuum line on front, so I don't know what would be best.

    Truthfully I have never seen a stock or near stock motor need more then 13 PSI. Unless your a big cam big horsepower high RPM engine the VFPR is a pain to tune because when vacuum drops it adds pressure. Changing your tune. I think this is better left to race cars.

    I just did a big block Mopar over 400 HP and only needed 17 PSI with Big Block Chevy injectors to keep VE in check at high RPM WOT. With these built engines you need enough fuel at WOT high RPM first! Then tune idle and mid range. If you do idle and mid range first without doing math then you go lean WOT. Not good!

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  8. #8
    Fuel Injected! mudbuggy's Avatar
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    Re: TBI Adjustable Pressure Mod

    I don't think you understand what I'm attempting to ask and I don't know the correct termmanology to ask another way. I want to extend the adjuster past the bottom of the tbi bottom unit so that I can adjust the pressure of the bypass spring while it is attached to the unit. My biggest fear is that I will drop a screw through the paddles and I won't be able to retreive them and/or they will damage an valve. So I am attempting to come up with a way to avoid having to remove the top of the tbi to adjust the pressure.
    1989 GMC V1500
    2002 Chevy Trailblazer
    1988 Dodge Ramcharger

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    Re: TBI Adjustable Pressure Mod

    Oh! Yes just run it through that hole in the picture.Some you have to drill hole, just looked at 2. It's just metal base for air cleaner about 1/4 inch to drill through. Easier to get to but not a lot of room there with the MAP hose.

    When I said to hook it up to fuel lines and test pressure you do this when the entire TBI is off being rebuilt. When the injector pod is back together hook it up and test. Adjust pressure, then disconnect from fuel lines and install on TBI unit. Then put the entire unit on truck.

    Even on vehicle you need to remove fuel lines, remove adapters into injector pod, remove air cleaner bolt, then there is only three torx bolts to remove that will not fall through closed throttle plates and to easy to hold on to so they don't. Most adjustable regulators and almost impossible to adjust on TBI. I did one once by drilling the hole, but then need an allen wrench trimmed half way, then I could do it 1/8 turn at a time... pain.... half turn is about half pound... then there's the spring. I don't know how far it will bring pressure up before needing aftermarket spring.

    If I hadn't said it I have never made one from stock. If I needed one I bought one. Just saw an polished aluminum one on Amazon for $58.

    I know some guys want to play with fuel pressure while tuning but I don't. 13 PSI will handle stock to plus 50 plus HP with tuning. Big HP motors I start at 1/2 pound over what math says it needs to be. Hardly ever touched one again this way.

    Maybe there's a better way. Build it and they will come!

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  10. #10
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    Re: TBI Adjustable Pressure Mod

    I'll take pictures of what I have done so far tomorrow, don't think I'll do it from my pda, I'll wait until I get home and do it from the laptop. It was all factory, I have the adjuster freed up and moveable if the base wasn't in the way so I figured out where to drill and hogged it out to a 5/16" hole with the mill. Don't know how much of the return fitting I can get into so I just played it safe. I am wondering what I can do with the vacuum tit on the base if I can move it or relocate it to another port just so I can get the adjuster to extend further down. Guess in my old age, and smashing my hands with my 3lb sledge means I can't get my fingers in the tight spots as easy as when I was younger. Now I guess I could cut the tit short and add a 45 degree elbow on the fitting to allow more room under there just so it can be adjusted while it's running. At least that the idea that I had when I started this part of the tbi rebuild.

    On a different topic but the same subject what does removing the radius of the bowls accomplish?
    Does the tbi spacer help atomize the fuel air mixture?
    Should I get a replacement fuel pressure spring while I'm doing all of this?
    Has anyone ran into a fuel pressure regulator spring loosing compression over its service life?

    Sorry to bore anyone, but as I have said before Murphy gets a hard on for me! lol
    1989 GMC V1500
    2002 Chevy Trailblazer
    1988 Dodge Ramcharger

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    RIP EagleMark's Avatar
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    Re: TBI Adjustable Pressure Mod

    Quote Originally Posted by mudbuggy
    I'll take pictures of what I have done so far tomorrow, don't think I'll do it from my pda, I'll wait until I get home and do it from the laptop. It was all factory, I have the adjuster freed up and moveable if the base wasn't in the way so I figured out where to drill and hogged it out to a 5/16" hole with the mill. Don't know how much of the return fitting I can get into so I just played it safe. I am wondering what I can do with the vacuum tit on the base if I can move it or relocate it to another port just so I can get the adjuster to extend further down. Guess in my old age, and smashing my hands with my 3lb sledge means I can't get my fingers in the tight spots as easy as when I was younger. Now I guess I could cut the tit short and add a 45 degree elbow on the fitting to allow more room under there just so it can be adjusted while it's running. At least that the idea that I had when I started this part of the tbi rebuild.

    On a different topic but the same subject what does removing the radius of the bowls accomplish?
    Does the tbi spacer help atomize the fuel air mixture?
    Should I get a replacement fuel pressure spring while I'm doing all of this?
    Has anyone ran into a fuel pressure regulator spring loosing compression over its service life?

    Sorry to bore anyone, but as I have said before Murphy gets a hard on for me! lol
    Sounds like he got the best of you? Hard on your fingers, it's all tight spots. Looks like another old gu here with me and projecttomany...trying to hold our own against these young guys.

    But the easy way to get to 13 I told you above.

    MAP line has to go there! If you could shorten it and use a GM elbow from a MAP line it would be fine if it gives you room. Spring will be fine to 13. My 1990 Sububan TBI has never been touched 149K miles, still has 13 PSI. TBI spacer is snake oil unless it's A CFM Tech one that has an opening at bottom was tested to give more power, but very small... also their hypertech power charger works, and you will never guess what else is on this page?
    http://marine-performance-parts.com/gmt ... mance.aspx

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  12. #12
    Super Moderator Six_Shooter's Avatar
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    Re: TBI Adjustable Pressure Mod

    Running MAP and FPR off the same vacuum line is perfectly fine. Many OEM applications are set-up this way.

    People forget that vacuum in this sense is not flowing air, but more like a spring or cushion of air, that only moves a little bit, or rather gets stretched under more vacuum.
    The man who says something is impossible, is usually interrupted by the man doing it.

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    RIP EagleMark's Avatar
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    Re: TBI Adjustable Pressure Mod

    Darn smart kids!

    All I know is vacuum sucks!

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  14. #14
    Fuel Injected! mudbuggy's Avatar
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    Re: TBI Adjustable Pressure Mod

    pics This is what I have as of now. I am also have had my brain working overtime today for the tbi. How do I test the tps and the iac while it's disconnected from the vehicle?
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    1989 GMC V1500
    2002 Chevy Trailblazer
    1988 Dodge Ramcharger

  15. #15
    Fuel Injected! mudbuggy's Avatar
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    Re: TBI Adjustable Pressure Mod

    more pics

    I am thinking that I can attach a piece of elbow to the port fitting coming off of the tbi housing then run it to the map sensor. Then I can drop the adjustment screw out the bottom without a lot in the way.
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