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TBI Injectors not pulsing

Discussion in 'The Garage' started by DgtlEnvrnmnt, Aug 2, 2005.

  1. DgtlEnvrnmnt

    DgtlEnvrnmnt Newbie

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    i had previously had a thread on here but i can't find it now so here goes. 1992 GMC Sonoma 4X4, 4.3L. Throllte body injectors won't pulse. Checking wiht a noid light and one injector gets a quick signal, but just one. i need to replace both pigtails as one looked pretty fried. but my question is, what are the injectors wired to? according to the haynes manual, 2 wires go to the ECM and the other two connect shortly after the Throttle Body and then go to the underhood fuse realy center and TCC/Brake Switch. Does this sound right? and where is the underhood fuse relay center and what is TCC?
    I've already ruled out a bunch of options such as having the Ignition Control Module tested, replacing the fuel pump, filter, relay and injectors. and i replaced the ECM as well. i know the injectors are getting gas they just aren't delivering the gas to the engine. thanx
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Not sure if you can get to these pictures or not. The chart is for TPI, same principle though.

    Really supposed to know if the ECM is seeing the firing pulses from the module, which is why you are supposed to have a scanner for this. Module testing is ok, but I don't think it accurately replicates what's going on when installed in the vehicle. Unless they test it ON the vehicle.

    Anyways, next up is spark, if you can't test to see if the ECM is getting a distributor reference pulse.

    Someone else should be able to comment if TBI injectors are wired up like this. Don't see why GM would change how they are wired.

    Wiring differences in injectors compared to that diagram aren't going to matter too much, if anything there will just be fewer wires, again, basic concept is the same.
     
  3. Thunder

    Thunder 3/4 ton status

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    If your pick up coil in the dist is bad the ECM wont see a signal and shut off the fuel
     
  4. DgtlEnvrnmnt

    DgtlEnvrnmnt Newbie

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    ok, after i replace the pigtails on the injectors (they are definately needed) and i still get no fuel, what should i do next? i have run out of ideas and this is my first experience with TBI, i'm used to carburetors
     
  5. chevyjeff

    chevyjeff 1/2 ton status

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    Could be the oil pressure switch. It also could be fuel pump or relay. Do you hear the pump kick on for 2-3 sec when ign key is turned on? Do you have spark while cranking? if you hear fuel pump and have sprak i would bet on oil pressure switch. No spark and i bet you module is toast
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    Oil pressure switch can't stop the fuel pump from working, only enable it. It's wired in as a bypass for the fuel pump relay/ECM drivers. If the relay fails, the oil pressure switch allows voltage "around" the relay to the pump.

    Sole purpose of the oil pressure switch is to enable the fuel pump if the relay/ECM doesn't. (failed)

    First diagram posted here shows the circuit for the oil pressure switch, if needed for clarification.
     
  7. TJS

    TJS 1/2 ton status

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    You have a bad pick-up or module in the dist. as was mentioned before. This sends a "signal" to the ECM to fire the injectors. Also check the magnets on the reluctor wheel on the dist. shaft when you have it out. Also use GM parts for this and not aftermarket. I usually replace the module and the pick-up at the same time.
    T.J.
    www.tjsperformance.com
     

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