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need backup on TBI

Discussion in 'The Garage' started by fatbob, Mar 29, 2006.

  1. fatbob

    fatbob 1/2 ton status

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    I got a 1988 crewcab and need some wiring help with the stock TBI.:confused: The original 350 motor threw a rod, so I put in a used 400 with the tbi heads and all the injection stuff. I realize that I may need to tweak it a little to get it to run the best on the 400, but it started and ran pretty decent, EXCEPT it had a bad knock.:doah: So out comes the engine, in goes another crankshaft, and back in it goes. Now I cant get it to start, unless I pour some gas down the thottlebody.
    I tried the flowchart at chevythunder, but I have to stop at the injectors cause I dont have a noid light, I thought I've read an article on making one but I cant find it ,. Now I do have power at both injectors, but cant tell if they are being pulsed. I cant hear the fuelpump since its pretty far back in the crewcab, my hearing is not the best, and most test say to listen for the pump to go on. I also cannot find the wire for the oil pressure switch, which will shut off the fuelpump, but it shouldn't prevent it from starting. I need to know what color wire to look for and if there is a wire for the temp sensor in the head. I may just have the wire hooked up to the wrong place.
    Last and most likely is at the fuse block. I have power everwhere BUT at the ecmfuse and the crank sensor fuse. Why would they not have power and everything else does? And I dont remember any crank sensor on the engine, and I DID have this 400 running in it before.:confused:
    I've been researching this damn problem for weeks, but I finally give up and am calling in the troops for backup.:bow:
    HELP
     
  2. 1985_K5_Silverado

    1985_K5_Silverado 1/2 ton status

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  3. SUBFAN

    SUBFAN 1/2 ton status

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    The beauty of TBI is you can look down the throat and see if it is getting gas....

    With a new crank, I would be more inclined to thing timing. Did you get the timing chain lined up right? Is the distributer dropped in correctly?
     
  4. jays68yak

    jays68yak 1/2 ton status

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    Make sure you are getting power to your fuel pump. That was my problem.
     
  5. chevyk2500hd

    chevyk2500hd 1/2 ton status

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    If ignition control module is bad then it wont tell the computer to supply any fuel.
     
  6. fatbob

    fatbob 1/2 ton status

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    Thanks 1985_K5_Silverado, for the links. They helped me get the oil pressure wire hooked back up. And in diagram #6, the picture of the fuse block shows a 10a and a 3a fuse in the bottom center/left. These are not getting any juice, which could be the main problem.

    SUBFAN, Did you notice that it ran when I poured gas in, which might imply that the timing may be ok. And the ugly thing about TBI is when no gas is flowing, you have to figure if its cause of the fuelpump, fuelpump relay, ecm, injectors, ignition control module, or just maybe a connector not fully seated or a bad wire.:wink1: That makes the old carb look prettier.

    jays68yak, I tried appling power to the test connector on the pump relay, but no joy. Like I said, the crewcab is so long and my hearing is so bad, I couldnt hear it even if it was running, so I still cant rule that out.

    chevyk2500hd, yeah but would it even tell it when to fire the plugs? Remember, it will start if I pour gas in it.

    Thanks for the replies guys, keep em coming.
    Anyone have any ideas about those fuses for the ECM. This thing has duel gas tanks, so I doubt both fuelpumps went out at once. I'm leaning more towards the idea that computer is not getting power so it cant tell the pump to turn on. What do ya think.:ears:
     
  7. fatbob

    fatbob 1/2 ton status

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    TTT
    any more ideas?
     
  8. mouse

    mouse 1/2 ton status

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    Make sure the fuel pump relay is getting power during the 2 second prime, before starting. Since you can't hear the pump ou'll need a second person to either listen or watch a multimeter/load light at the relay. The computer sends the ground to the injector circuit, and the power side of the circuit must have power when ever the switch is to "Start" or "Run." I believe its possible you do not have power during start.
     
  9. Jonny-K5

    Jonny-K5 1/2 ton status

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    2nd that.
     

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