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Need TBI help...backfiring

Discussion in 'The Garage' started by clarkjw24, Oct 1, 2005.

  1. clarkjw24

    clarkjw24 1/2 ton status GMOTM Winner

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    I've had tbi on my k5 since dec. Its always ran great. But over the last month its started studdering and backfiring. I thought it was just a burnt plug wire but I changed them today and it didn't help it. It will crank and idle great. Put it in drive and it wants to die. Pull off and give it the gas and it studders and backfires to the point I can't go over 5mph. Could someone please give me some ideas of whats going on here. I think its a lean backfire, could it need a new fuel filter or is one of the tbi sensors gone bad?
     
  2. sapper

    sapper 1/2 ton status GMOTM Winner

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    The coil, mine did the same thing
     
  3. 4xcrazy

    4xcrazy 3/4 ton status

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    Mine did that when i had weak fuel pressure, pump was dying out.
     
  4. randy88k5

    randy88k5 1/2 ton status

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    Read the plugs, see what they say. Either too lean or too rich. Start from there. Could be coil, sensor, map, egr, etc... Have to start isolating different areas. Let me know what you find, Ill try to help to the best of my knowledge...
     
  5. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    Is it not throwing any codes?
     
  6. clarkjw24

    clarkjw24 1/2 ton status GMOTM Winner

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    I changed the coil and its still doing the same thing. I haven't pulled the plugs but I will in the morning. I'm pretty sure that its a lean backfire. I guess I should finish hooking up the adl port to check for codes. :o God I hope its not the sending unit. I really don't have the cash to buy a new one. I may pull the fuel filter also and replace it in the morning.
     
  7. dheavychevy38

    dheavychevy38 1/2 ton status Premium Member

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    Mine just got done doin the same thing it needed a complete tune up and now it runs great.
     
  8. clarkjw24

    clarkjw24 1/2 ton status GMOTM Winner

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    Tune up? Cap, rotor button, plugs, wires?
     
  9. beastofablaze

    beastofablaze 1/2 ton status

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    exhaust leaks might be another reason...If its running lean its either one of the sensors, the sending unit, or the filter.
     
  10. randy88k5

    randy88k5 1/2 ton status

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    Try to test things and isolate different areas of concern before you start throwing parts at it. That can get expensive real quick. After working retail for a good while, you see atleast 50% of the parts sold go onto a vehicle where that part wasnt bad to begin with, and people get more frustrated. Just take some time and go in a logical order...
     
  11. ryan22re

    ryan22re 1/2 ton status

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    running right yet?

    did you pull any codes?

    just wondering

    ryan
     
  12. clarkjw24

    clarkjw24 1/2 ton status GMOTM Winner

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    Is it possible that the o2 sensor is bad? Can advance auto check the fuel pressure?
     
  13. ryan22re

    ryan22re 1/2 ton status

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    dont think the o2 sensor could cause it. advance wont be able to check fuel pressure. they may sell the adapters needed to check fuel pressure though. i dont even have an adapter to check fuel pressure on a tbi even though i have two tbi trucks.

    any way you can get it to columbia/irmo area? its hard to diagnose one over the internet. got a tech 1 at the shop to pull codes/look at data. plus a discount on gm/acdelco parts.

    id be willing to help anyway i can.

    ryan
     
  14. 87BrnRsd

    87BrnRsd 1/2 ton status

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    I was thinking 02 sensor but I dont think they actually do anything until they heat up (at about 150-160 degrees). I dont really know what coud be causing this. Map sensor or egr maybe? Check the codes.
    -Harrison
     
  15. clarkjw24

    clarkjw24 1/2 ton status GMOTM Winner

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    I wish it was that easy. I don't have the aldl port hooked up. I guess I should do that and run to the local mechanic and see if its throwing any codes (which I'm sure it is). Also I don't have egr. This may sound dumb but which one is the map sensor?
     
  16. randy88k5

    randy88k5 1/2 ton status

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    Manifold Absolute Pressure sensor is behind the AIR pump diverter valve (the black hoses that run to the AIR pump). It has a plastic vacuum hose that goes to it, and a three wire connector. Its rectangular, and a little bigger than a big pack of chewing gum.
     
  17. clarkjw24

    clarkjw24 1/2 ton status GMOTM Winner

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    Does anyone have the diagram to tell me where the wires for the aldl port go. I had a drawing once but I can't find it now. Is there anyway to check the map sensor? I don't think I've got an air pump (thats the smog crap right?)

    This is it right?

    AS5.jpg
     
  18. randy88k5

    randy88k5 1/2 ton status

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    [​IMG]

    Yes, that is the MAP sensor. You can hook a vacuum pump to it and read the corresponding voltage output. It needs to fall within a certain range.

    I assumed you had the AIR stuff, sorry bout that
     
  19. clarkjw24

    clarkjw24 1/2 ton status GMOTM Winner

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    I'm going try to figure this out. I'm at work right now so I'm trying to remember what I have done.

    Ok so "F" and "D" is just a ground for a shift/code light. Will any two wire light work? (like old dash lights, park sockets) Ground it here and give the other wire a 12v acc power.

    "E" "B" "M" i've got no clue but think those are the ones I've got hooked up. IIRC these wires came out of the ecm. Maybe yellow?

    "C" does this just need to be grounded? and what is it?

    "G" straight to a constant 12v?


    Also anyone here making aldl to DB9 cables or know where I can get one quick. I've got less than 12 days to get this thing going again. I've got a laptop and can download the software.
     
  20. ryan22re

    ryan22re 1/2 ton status

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    if you can wait till in the morning i can tell you what color wires go where in my 87 k5 as far as the aldl is concerned.

    ryan
     

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