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TBI Blues.....(long post)

Discussion in '1992-Present Chevy & GMC models' started by ford_assassin, Mar 22, 2004.

  1. ford_assassin

    ford_assassin 1/2 ton status

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    Hey guys, not a K5 question, but still a Chevy.

    This one has me stumped.

    Here it goes. My wife's '91 Caprice Classic is having issues. The car has a 5.0 (305), 700R-4, 3.42 posi rear, and the normal 2bbl TBI setup you'd find on some Camaros, and all '87-'95 trucks. The original motor, trans, and rear end all have just under 300,000 miles on them. Until now you'd have never known or guessed it had that many miles on it because it still runs great. Up until this problem, I have only changed the water pump, Alt, knock sensor, fan clutch and fuel pump.

    It all started in November of '03. My wife came to me and says that the car likes to fall on its face ramdomly when taking off from a light. I check for codes first and nothing is stored. So I change the fuel filter, run a few bottles of "fuel injector cleaner" through it and nothing changes and it still does it on occasion just like before.

    So, some time passes and nothing really gets worse and to be honest I didn't have the money to mess with it anyway. Then last week she wakes me up one morning and says it won't start. She also tells me its been giving her "check engine" lights on her way home for the last few days and forgot to mention it to me (women!). Again, I check for codes with my scanner and to my suprise....nothing is stored. That in itself is odd to me why she would she a light, but the ECM didn't store it.

    Anyway, I crank the motor for a good 30 seconds and it finally starts and idles very smooth once running. I rev the motor alittle while still in PARK and the motor stumbles, everytime I rev.

    Doesn't matter if I do it slow or fast, it stumbles just off idle. I took it for a drive and had it die on me when leaving a stop(s) if I gave it more than the tinyest amount of peddle to get moving. I was able to get to 65 mph, once it got to speed it drove fine.

    I get it home and do a complete tune up. I changed the cap, rotor, wires, plugs, change the oil, air filter, another fuel filter, and thermostat. No change.

    Then I changed the ignition coil (external), MAP sensor, tested the ignition module, checked the timing, and checked the fuel pressure after the fuel fiter (near the pump) and at the TB, both inline, both read 12 psi. The book says it needs to be between 9 and 13 psi. That means its its not the pump or the fuel pressure regulator, right?

    Still no codes either.

    At this point I am totally stumped. If any of you have any ideas, please tell me. If you need more info that I didn't mention, just let me know.

    Thanks guys.
     
  2. sled_dog

    sled_dog 1 ton status

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    fuel pressure regulator is located in the TB itself. So when you get it idling take the filter off and look at the the injectors. Definetally soounds like a fuel issue, look at the the injectors and look for a good spraying mist. If its just dripping or seems a little slow on the pulses then you may have a FPR or injector issue.
     
  3. ford_assassin

    ford_assassin 1/2 ton status

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    [ QUOTE ]
    fuel pressure regulator is located in the TB itself. So when you get it idling take the filter off and look at the the injectors. Definetally soounds like a fuel issue, look at the the injectors and look for a good spraying mist. If its just dripping or seems a little slow on the pulses then you may have a FPR or injector issue.

    [/ QUOTE ]

    The injector spray looks good. We even compared the spray to a buddy's '92 truck and both looked the same.

    Thanks for the suggestion though.
     
  4. bowtiepower00

    bowtiepower00 1/2 ton status

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  5. Confedneck

    Confedneck 3/4 ton status

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    fuel pump... only does it at times.. im betting your pump is shot..
     
  6. Pookster

    Pookster 1/2 ton status

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    I'd definately check for fuel flow issues- TBI's tend to be very forgiving at idle, and not so good at WOT. If you start up the car, run the car.

    Watch the fuel flow as someone womps on the gas. if you dont see a great change in fuel delivery, I would not guess the fuel pump as the first check. (while it may be the culprit, I'd check other things first).

    You have to make sure the impedance of the injector is up to par. Just because the injector functions at idle, (normal state) doesnt mean its opening up properly.
     
  7. ford_assassin

    ford_assassin 1/2 ton status

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    [ QUOTE ]
    I'd definately check for fuel flow issues- TBI's tend to be very forgiving at idle, and not so good at WOT. If you start up the car, run the car.

    Watch the fuel flow as someone womps on the gas. if you dont see a great change in fuel delivery, I would not guess the fuel pump as the first check. (while it may be the culprit, I'd check other things first).

    You have to make sure the impedance of the injector is up to par. Just because the injector functions at idle, (normal state) doesnt mean its opening up properly.

    [/ QUOTE ]

    When doing the fuel pressure checks I was driving the car. I had it die on me while still maintaining 12 psi. The needle didn't even move when I floored the gas, then it stalled out.

    I even compared the injector spray with a '92 truck with the same TBI setup side by side.....looked like a mirror to each other. The spray flow doesn't change when the motor stumbles either.

    Either way if I can find out what the deal it tomorrow, its going to the dealer on Thursday. They have a policy of if they don't fix it or find it, you don't pay.
     
  8. COCHEV

    COCHEV 1/2 ton status

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    have you checked your timing? if the timing is too retarded it could make it stumble under accel. make sure you disconnect the little brown and black wire when you do it.
     
  9. 4xcrazy

    4xcrazy 3/4 ton status

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    [/ QUOTE ]
    When doing the fuel pressure checks I was driving the car. I had it die on me while still maintaining 12 psi. The needle didn't even move when I floored the gas, then it stalled out.


    [/ QUOTE ]

    I had a similar problem with a previous car i owned, checked the fuel pressure, stable at whatever it was supposed to be, don't remember right off now, but when you hit the throttle, the pressure is supposed to jump up some to adjust for the increased engine rpm. Similar to the carb'd accelerator pump. Fuel pumps i have seen do some weird things, some go out over time while losing pressure alittle at a time, some just die all of the sudden, some act up at different times and work great at others.
    If ya don't want to deal with it, or dump money into the problem and not figuring it out right away, my suggestion would to take it to the shop and have them throw it on the computer diagnosis and figure it out the easy way.
     
  10. ford_assassin

    ford_assassin 1/2 ton status

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    [ QUOTE ]


    ....my suggestion would to take it to the shop and have them throw it on the computer diagnosis and figure it out the easy way.

    [/ QUOTE ]

    It just keeps getting better and better.

    Dealer #2:
    Bob Williams Chevrolet called about a hour after I dropped off the car (around 9 am). They told me its the fuel pump, I was pretty quick to comment that I checked the pressure at idle and under load while driving and it always maintained pressure at 12 psi.

    They insisted that was the problem and said if it wasn't, they would just pull it back out and not charge me.

    4:30pm rolls around and I am just signing off of work. My cell phone rings, guess what? "Mr. Bright, we changed the fuel pump, but its still doing the same thing. We have three other techs helping your guy troubleshoot the problem right now."

    At this point I am laughing to myself over the whole thing.

    He tells me that they aren't going to charge me any extra if they find the real problem with the car. He also adds that will be keeping the car another day.

    Six mechanics, two different shops, and still a sh!tty running Caprice.

    What a great day.
     

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