T.B.I. problems

Discussion in 'Troubleshooting & Diagnosis' started by biza1970, Dec 30, 2007.

  1. biza1970

    biza1970 New Member

    6
    0
    Apr 26, 2004
    NJ, USA
    aight....got a 350, 700r4, first time with F.I. Basic GM T.B.I. It runs ok BUT.........its hard to start and has to warm up for at LEAST 1/2 hr before it wont stall upon giving it any gas over 1/16 throttle. And after that, will still stall or hesitate BADLY whenever the throttle is hit too hard. so far, no check engine light, no apparent vacuum leaks, or broken wires and the guy i bought it from said all the sensors and stuff were new, but im begining to think he should die cuz i already found out he lied about the rear brakes being all"brand new". Oh yaa, it idles very high too.....ANY IDEAS!?!?!? PLEASE HELP.....please getting out into traffic is damn near IMPOSSIBLE and i dont want to die...had a few close calls already
     
  2. GoldenOne7710

    GoldenOne7710 Veteran Member Lifetime Gold Member

    4,358
    225
    Jun 23, 2004
    Athens, GA
    The fuel pressure regulator in those will cause those symptoms. They are basically junk from the factory. The little spring inside them is fragile and will eventually break in most cases. Replace it with an aftermarket unit. The one from Holley is fairly priced and it's adjustable. It may be a good idea to completely disassemble your whole TBI unit and overhaul it. Kits are available from most parts stores. Go to http://tbichips.com and read up on some easy DIY upgrades on GM TBI setups. Also check out the TPS.

    When is the last time you had the entire engine tuned up?
     
  3. Knuckle Dragger

    Knuckle Dragger Moderator Staff Member Lifetime Gold Member

    13,282
    467
    Nov 2, 2002
    Waddell AZ
    Do a good visual inspection, vacuum leaks tune condition etc, then check for a partially stuck open EGR valve. ;)
     
  4. Kamikaze

    Kamikaze Veteran Member Lifetime Gold Member

    +1 What Golden One stated!

    The TBI Fuel Pressure regulator is a common problem.
    You will need a set of Torx T-15 drivers to disassemble the unit and access the regulator. The regulator is on the back of the injector cluster that is on top of the throttle body.

    After you remove the two wire connectors on top of the injectors, you will need to use a flare nut wrench on the backside of the throttle body to remove the fuel lines. Be careful you don't loose the o-rings on the lines or better yet, get replacements.

    Undo the Torx screws on the top of the cluster and pull the unit free of the throttle body. Flip the cluster over and undo the screws holding the pressure regulator. There will be a diaphragm and a spring under the housing. Now would be a good time to replace the regulator with an adjustable one from Turbo City or any other aftermarket brand unit. The adjustment knob is accessed under neath the rear flange behind the throttle body. It's tight but can be done if your hands aren't too large. Be sure to use a new diaphragm as this is a common problem as well as new pressure spring.

    I would also carefully remove the two injectors at the front of the cluster and inspect the filter screens and nozzles. Don't poke them, just use carb cleaner spray to remove and clean them out.

    At this point, you could also install a injector riser under the throttle cluster. This goes between the throttle body and the injector cluster and is sandwiched between the gaskets. This enhances the throttle response. This is also something that Turbo City and Trans-Dapt sells.

    Once eveything is cleaned out and reassembled, you should have eleminated the throttle body itself as a problem. If you have an adjustable timing light, you could use it to illuminate the spray pattern of the injectors as the engine runs. It should have a nice even flow pattern like a wide shower head.

    Some other areas that can affect the idle speed and overall drive ability could be a mis-adjusted throttle position sensor on the side of the throttle body. This is common as many people just un-bolt and install a new one without properly setting it. You will need a Ohm meter to do it correctly but sometimes, you could just loosen the screws and adjust it as it runs to get by.

    If there are any leaks to the MAP sensor, it could send false readings to the computer. Also, I would suggest checking the O2 Sensor. If the previous owner did a cheap replacement and used a universal or splice replacement, this could affect the overall performance.

    I've been through what you've described. It takes some patience and time but once you understand the systems, TBI is very basic.

    If you need more assistance, I would suggest you contact Tom Miller at Turbo City.
    http://www.turbocity.com/
    He is one of the most knowledgeable people on TBI stuff!

    Good luck!
     
  5. biza1970

    biza1970 New Member

    6
    0
    Apr 26, 2004
    NJ, USA
    I tuned it up today and it helped a little(plugs/cap/rotor), it just feels/sounds smoother, also goes a LITTLE easier when cold......the 02 sensor is a one wire ALLLLL the way back on the collector of the header.....it is a "splice" job.... maybe moving it up( which prolly wont help cuz it'll only be in one exhaust stream, right???) or a 3 wire/heated ive read about may help??? still no check engine light or vacuum leaks. The injectors have a nice spray pattern. I cant afford a new regulater or trick parts as of yet but guess i'll try checking the regulator to see for internal leaks or obvious damage.....??? THANKS for all the help so far......appreciate it....BBA
     
  6. 80ZGuy

    80ZGuy Veteran Member

    423
    0
    Jan 25, 2000
    Timmins,Ontario,Canada
    What year/make/model vehicle are you working on? I'm guessing an 87-95 GM Truck correct?
     
  7. biza1970

    biza1970 New Member

    6
    0
    Apr 26, 2004
    NJ, USA
    ya, 87 burb, lifted, great shape bod-wise, BUT i also have a real nice 1970 Camaro with a 454,tunnel ram, dual quads, roller cam and all the trimmins.........that aint runnin either damnit....nasty fuel problem....dirt in the tank.....you guys have helped me with that in the past.....some good advice...figured id try again with this....a friend of mine said a new regulator probably a good idea, as well as a heated 02, and check the map sensor.....
     
  8. Brian79Z

    Brian79Z Veteran Member Gold Member

    382
    1
    Oct 30, 2005
    NW Ohio
    This also sounds like a classic fuel pump issue.

    Check the fuel pressure. On a 1987, I'd almost bet a fuel pump.
     
  9. TheFly

    TheFly Guest

    do the wires
     
  10. Brian79Z

    Brian79Z Veteran Member Gold Member

    382
    1
    Oct 30, 2005
    NW Ohio
    make sure they're not Autozone wires either.... junk junk junk
     

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