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TBI bucking issue..

Discussion in 'The Garage' started by ryoken, Jun 4, 2004.

  1. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    hey guys... been running my new 87 around for a week or so and its developing a bucking/surging issue when you back off the throttle at slower speeds. does it mainly at off idle speeds when i'm poking around the boatyard. holds an idle fine and smooth tho a little high. once your into the pedal at all, its smooth. it does it mainly below 30mph, runs fine at 65. its when your totally off the throttle..

    80 grand on the 350 TBI, 700r, 3.73's.. new fuel filter,, plugs, wires, cap, rotor, pvc, air filter (needed all that pretty bad, no change). its throwing no codes (was kinda expecting to see one).

    i figured it was a vacuum leak, but damned if i can find one. did the ether trick, couldn't find anything, and its pulling about 20 or so lbs at idle on the gauge.

    any suggestions on things to look at? i'm a carb guy so the TBI stuff is pretty unfamiliar to me... thanks for any pointers. /forums/images/graemlins/smile.gif
     
  2. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Soft codes = failures the computer sees but doesn't ttrip a light.
    Hard Codes= Trips light.

    Read the codes and see if it has any soft codes.

    Get some carb cleaner. Spray the lines and the base of the TBI. That will find any leaks.
    Check the adjustment of the 700R4 TV cable.
     
  3. bassmannh

    bassmannh Registered Member

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    my 87 did the samer thing, pulled off the vacuum hose to the eger and plug the hose with a golf tee as a diagnostic tool only and what do you know know more stumble, had to replace the egr solenoid and egr valve because it was coming in too soon, gm dealer solenoid was on 10 dollars and some change, aftermarket solenoid was over 50.00, but aftermarket egr was cheaper, try this trick, to check egr problem, I have 2 87's one blazer, one burb, both did the same thing.....
     
  4. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    please excuse my EFI ignorance. /forums/images/graemlins/blush.gif

    how can i retrieve the "soft codes"? i used the list and instructions from here http://www.cfm-tech.com/gm_tbi_trouble_codes.htm

    is that all of them?

    i'm assuming this
    [​IMG]
    is the EGR? /forums/images/graemlins/confused.gif i just tried plugging the small line while running to the store, no help...

    and out of curiosity, can someone tell me what this is?

    [​IMG]

    just read up on TV adjustment. not sure if thats an issue, it seems to shift pretty normal...

    thanks for the advice, i can see i'm gonna get a crash course in TBI.. thank god the boating industry is 20 yrs behind the times. we just started playing with EFI a couple years ago. /forums/images/graemlins/eek.gif /forums/images/graemlins/rotfl.gif
     
  5. xdelirious45x

    xdelirious45x Registered Member

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    For the first picture, I know that's your AIR pump and the EGR valve should be on the passenger side of the intake manifold. it should be bolted in a 45 degree angle right next to your throttle body.

    The second picture air A.I.R. hoses that should be bolted to your exhaust manifolds but only the #1&#3 cylinder exhaust port on the driver side and #2 & #4 exhaust port on the passenger side. There should be a connecting aluminum pipe that runs behind your distributor. It should be a "[" shape connected those two pipes.

    Hope this helps
     
  6. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    well, after my stupid a$$ found the EGR and blocked it off (new one will be in monday), it corrected the stumbling issue. runs great (thanks), but now after putting about 40 miles on it today, the tranny is acting all screwed up. like a TV adjustment, the shift points are all screwed up. doesn't come out of first till like 35 mph.. so i know what i'll be doing sunday, learning how to adjust it /forums/images/graemlins/wink.gif hope its just that and not the 700r taking a dump.. /forums/images/graemlins/eek.gif
     

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