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TBI Driveability problems.

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by zcarczar, May 15, 2003.

  1. zcarczar

    zcarczar 1/2 ton status

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    Ive been dealing with TBI driveablity problems ever since Ive had my truck and im getting sick of it. Ive had a GM driveability tech look at it a couple times and he hasnt been able to diagnose it for me.

    So far my troubles have been really bad hesitation off idle or from no throttle to acceleration in traffic. The tech has said it acts like it is running lean which doesnt make any sense to me because it smokes some nice thick black smoke sometimes which would indicate its running rich. Sometimes while accelerating it will almost act like its surging, like the ESC is advancing and retarding the timing based on a knock signal or the EGR is opening and closing causing the truck to run good for a moment then fall flat on its face.

    The only codes it has set is 42 and 43. I got 42 once and I get 43 a lot. The Knock Sensor is pretty new and has been replaced by me a couple times so i doubt thats what it is.

    Does anybody have any ideas what might be causing this? Im sick and tired of my truck running crappy and getting crappy mileage from me having to literally floor it to get it moving to keep up with traffic. /forums/images/graemlins/1zhelp.gif
     
  2. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    Have ya changed the fuel filter?
     
  3. MOTORHEAD

    MOTORHEAD Registered Member

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    Check your EGR vavle as well. When these go they rob your manifold of vacuum.
     
  4. Thunder

    Thunder 3/4 ton status

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    Code 42 can be the following: Bad Distributor module, bad magnetic pickup coil( there can be a miss fire or hesitation when cruising, say at 45 mph in high gear with a bad mag coil also) Or a possible short somewhere in the wireing.

    Code 43 bad knock sensor, bad ETC module, Or can come up as a result of a lean mixture, caused by a stuck EGR valve or low fuel pressure(clogged filter or bad pump).
    If its putting out a lot of black smoke you might want to look into the 02 sensor also.

    The TPS can also affect the way your truck runs similar to your description.

    A Bad Coolant temp sensor will make it run rich by telling the computer the engine temp is only 90 degrees causing it to richen up the mixture. Kind of like driving with the choke on.
    Well thats about all i can think of.
    I really encourage you to get a scanner like an AutoXray or WinALDL. It will tell you the operating values of all the sensors and if they are working or not. By the time you go replacing a bunch of sensors you will have payed for one.
    If you have a lap top, WinALDL is a free download.
     
  5. zcarczar

    zcarczar 1/2 ton status

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    I changed the fuel filter a little under a year ago, I will try that again. I doubt its the EGR because I've driven around with the vaccum port to the EGR plugged and it made little difference in the driveability. Im leaning towards thinking my problem is in the O2 sensor because I havent replaced that yet and i dont know how old it is.

    I have a GM Tech 1 and WINALDL to use. Ive checked out all the sensors and they are all functioning properly.
     
  6. Thunder

    Thunder 3/4 ton status

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    Good you have a scanner /forums/images/graemlins/thumb.gif

    To check the 02: look at the 02 Mv it should bounce around between 400 and 900 mv if it holds steady or is way high or low change the 02
    Also check the 02 counts if I rember right it should vairy too. If it holds steady all the time its a bad 02.
    You can have a bad 02 without lighting the CEL. The computer only looks for low/high voltage or shorts. If the 02 doesn't work right but holds a steady voltage within its operating range the ECM thinks everything is ok.
    Its a good idea to replace the 02 every 50K miles. Or if it has been running rich it can get clogged up with deposits and not work right.
     
  7. MousePowrd

    MousePowrd 1/2 ton status

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    Do you have a catalytic converter? Could be plugged.
     
  8. zcarczar

    zcarczar 1/2 ton status

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    The 02 sensor reading jumps all over the place. Usually from .0something to .9something. I do need to check to 02 counts because i havent really checked that.

    Another thing the tech and I found is that my IAC counts are WAAAYYYY to high. When I put it in drive while its stopped, the IAC count nearly maxes out, and the truck idles too low for a stock engine and tranny, around 600 and 625 RPM's. This could also mean that I may have a crappy Tourque Converter that the PO installed.

    The Cat is brand new as of a about 1k miles ago and so is the exhaust from the headers back.
     
  9. k20

    k20 3/4 ton status

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    I second the temp sensor and EGR...
     
  10. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    O2 sensor is recomended to be replaced at 60k by most manufactures. they get lazy. Change it.
    I have had a serge at cruise and it turned out ot be a EGR problem. Un plug the EGR and see if it changes. should throw a code after about a mile. Now I swapped the EGR on mine yesterday but haven't drove it enough to see if it cured it. I On mine the EGR has a control solonoid and That's the next thing I will change. The service manul is real sketchy on testing procedure for this thing. The ECU is acting correctly because with the truck jumped into diagonostic, engine off, the valve closes. Now I'm dealing with a 454 so I'm not sure if yours is the same. The service manual does have a different section dealing with the 454 and HD 350.
    I would also verify the truck is going closed loop. If it's still running open loop it will run rich like hte choke is stuck on. That however goes agains the knock sensor being tripped so I'm leaning towards o2 sensor problem.

    Ohh it's possible that the EGR passages being blocked and causing some of this.
     
  11. zcarczar

    zcarczar 1/2 ton status

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    It goes into closed loop fine. I have checked the EGR by plugging the vacuum line going to the EGR valve and it helped a little but really didnt improve anything.

    Im also wondering if maybe it could be the engine. Maybe the cam lobes are worn and the valves arent opening properly or maybe I'm getting a bottom end engine knock under load causing it to set the knock sensor code. /forums/images/graemlins/tongue.gif
     

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