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No Spark, No Fuel, WTF

Discussion in 'The Garage' started by rhuarc31, Oct 30, 2004.

  1. rhuarc31

    rhuarc31 Registered Member

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    Got a 94 TBI. I've got fuel to the back of the throttle body, but none out of the injectors. Also have no spark. I've replaced pretty much the entire ignition system, and tried a new ECM. Any Ideas?
     
  2. 90v1500

    90v1500 Registered Member

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    What parts of the ignition have you replaced?
     
  3. k20

    k20 3/4 ton status

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    Were you sure to check the ignition module? It will do some weird stuff if it goes bad (sure to put the di-electric grease on the bottom of it), or, seems like i always say this, on my old 350, at one point the injectors wouldnt fire, spark looks kinda weak ( still had spark though) was the engine temp sensor located in the manifold.
     
  4. rhuarc31

    rhuarc31 Registered Member

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    Replaced cap, rotor, coil, pick up coil, module. And yes I used the grease. What's got me baffled is that the injectors are not kicking out fuel either, yet are getting fuel to the throttle body.
     
  5. Thunder

    Thunder 3/4 ton status

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    Checked your Fuses? There are 2 for the ECM. Grounds?
     
  6. 90v1500

    90v1500 Registered Member

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    /forums/images/graemlins/confused.gifMaybe the oil pressure sensor, it won't let the engine fire if the oil pressure drops or if the sensor is defective. You said you have fuel to the back of the TBI but what kinda pressure? Also had a pickup coil get cracked one time when I put the cap back on and it did the same thing (no fuel spray no spark).
     
  7. k20

    k20 3/4 ton status

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    yeh they dont have to fire, they just aint gettin an impulse to fire, I had forgotten about the Oil pressure sending unit, that would make sense, the computer is just killin everything to stop the motor and prevent damage. If you have access to a scan tool, get it, otherwise, prepare for a guessing game of $20 sensors.
     
  8. rhuarc31

    rhuarc31 Registered Member

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    Yeah, I forgot about that sensor too, I'll check it this afternoon. Thanks for the thoughts.
     
  9. HarryH3

    HarryH3 1 ton status Author

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    The oil pressure switch doesn't shut down the engine (unless the fuel pump relay has failed). It's there as a bypass around the fuel pump relay. If the relay isn't sending power to the fuel pump, then once the oil pressure comes up to 3 or 4 PSI the switch will close and turn on the fuel pump.

    You're on the right track with the ignition. The trigger to the ECM, to tell it to fire the injectors, comes from the ignition module. So typically, if there's no spark, then there will also be no fuel coming from the injectors. Make sure that you have power to the ignition module. It should have a steady 12 volts to it when the key is switched on. If I remember right, power comes in on the pink wire.
     
  10. miniwally

    miniwally 1/2 ton status Premium Member

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    That is correct Harry. I had this same prob. with my buggy on the trail one time. I did the same replace parts routine and nothing worked. When it did start the tested voltage at the battery showed over 12 volts prior to start up.
    We had run the battery down and charged it back up using an on board welder from a freinds rig. I would give your battery a good charge and see if it starts.
    The computer may not have the power it needs to do its thing????
     
  11. Emmettology 101

    Emmettology 101 3/4 ton status

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    [ QUOTE ]
    The oil pressure switch doesn't shut down the engine (unless the fuel pump relay has failed). It's there as a bypass around the fuel pump relay. If the relay isn't sending power to the fuel pump, then once the oil pressure comes up to 3 or 4 PSI the switch will close and turn on the fuel pump.

    You're on the right track with the ignition. The trigger to the ECM, to tell it to fire the injectors, comes from the ignition module. So typically, if there's no spark, then there will also be no fuel coming from the injectors. Make sure that you have power to the ignition module. It should have a steady 12 volts to it when the key is switched on. If I remember right, power comes in on the pink wire.

    [/ QUOTE ]

    When I swapped bback to TBI from a carb on my 89 3/4, I replaced everythign except the oil pressure sensor and we actually didn't realize it was missing(hoel was plugged though). Truck would fire or run... No fuel from the injectors, no spark.... Finally traced it down and found out we were missing the oil pressure sensor. Once I went and bought it and hooked up the wires, the truck fired and ran.
     
  12. duece21

    duece21 1/2 ton status

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    I had the same problem with mine and it was a damaged power connection at the firewall.
     

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