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Thread: No Injector Pulse

  1. #1
    Fuel Injected!
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    No Injector Pulse

    I am getting 12 and 15 pulsing on my service engine light. I cannot get the injectors to fire when trying to crank the engine. I just put this engine in and did all the wiring to the computer and sensors using the diagrams on this site. The engine is a 94' 350 and me and my buddie just did this on his truck in Jan. Now Im doing my own. Triple checked everything and still not getting any gas when cranking. I have the purple starter wire tied to c9 as indicated in the schematic. What could be the cause of this? I even replaced the cap and rotor and verified I am getting spark. Fuel pump primes when power is applied to ECM. I am lost now. Any suggestions out there? What could be the cause of the injectors not shooting gas? I am lost at this point and need to take a break off it for a few hours?

    EDIT: EagleMark split from other thread...

  2. #2
    Fuel Injected!
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    Quote Originally Posted by Tyree View Post
    I am getting 12 and 15 pulsing on my service engine light. I cannot get the injectors to fire when trying to crank the engine. I just put this engine in and did all the wiring to the computer and sensors using the diagrams on this site. The engine is a 94' 350 and me and my buddie just did this on his truck in Jan. Now Im doing my own. Triple checked everything and still not getting any gas when cranking. I have the purple starter wire tied to c9 as indicated in the schematic. What could be the cause of this? I even replaced the cap and rotor and verified I am getting spark. Fuel pump primes when power is applied to ECM. I am lost now. Any suggestions out there? What could be the cause of the injectors not shooting gas? I am lost at this point and need to take a break off it for a few hours?

    EDIT: EagleMark split from other thread...


    GROUND, GROUND, GROUND!!! Sorry, have seen it too many times. Check all your grounds for security and connectivity. They are vital to operation. If it is a transplant truck then definitely verify ALL grounds. Need good ground from battery to-->Body, Engine, Body-to-Engine, Engine-to-Frame. HTH

    Buddrow
    If it don't fit force it, if it don't force fit f&%@ it!

  3. #3
    RIP EagleMark's Avatar
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    Well the injectors also need 12 volt power going in, then the ECM grounds to fire them. So do you have fused 12 volt power to injectors?

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  4. #4
    Fuel Injected!
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    Eagle mark. Thank you or your reply. I have 12v power going to injectors on a switch. I have my ecm and dist on a switch also. I have 3 ECM grounds going directly to a pigtail on the negative battery terminal. The starter wire is to the block. I will add two more fat wires from the block to the body and a fat wire to the negative terminal to be safe and go from there. I have nearly given up and ran out of time. I will try again on Thursday morning. Thanks again. Its driving me nuts because I have done this before. I got a couple of drips out of the injectors about three times out of about 40 tries.

  5. #5
    Fuel Injected!
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    and thanks buddrow

  6. #6
    LT1 specialist steveo's Avatar
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    it's always the same, the injectors are powered constant, the ecm switches the ground, the ecm does so based on input from whatever reference it has; cam sensor, distributor or front mount, or crank sensor. if your ecm isnt trying to ground the injectors, you either blame the ECM, or you blame that positional refrence.

  7. #7
    RIP EagleMark's Avatar
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    Those grounds would be better off to say... intake manifold or block. Then negative batt terminal to block. That is the way factory has them wired. I forget why grounding to batt is not a good thing...

    As for power on stuff... I'm guessing this is a conversion and they always bring up issues. The way I like to power an EFI system on an old carb vehicle is an extra relay. Use the wire that went to points (with resister removed) to turn on this main EFI relay, then let that relay power on other things as well. I've seen them done with switches as you described but they always seem to have issues. Maybe it's not getting power at right times? Like one guy ran a switch instead of a fuel pump relay and turned it on manually, well sometimes he forgot, if you let it work like GM intended then when key goes on, fuel pump primes 2 seconds and goes off or stays on if you go directly to crank, then the crank wire also gives ECM signal at correct time, remember there's another wire off fuel pump wire back to ECM so it knows fuel pump is running. He had all sorts of strange starting issues. All we did was take out the switch and wired in the relay as it is stock and he never had another issue.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  8. #8
    Electronic Ignition! gearhead1's Avatar
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    I would check the pick-up coil as no signal = no pulse width.

  9. #9
    Fuel Injected!
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    yes i will be checking that tomorrow also. I am also taking the ignition module on the dist to be checked at autozone just in case I am doing everything right and it is a component failure. We will see. Thanks for the suggestion. I really appreciate the help on this website and I want to get my truck rollin.

  10. #10
    Fuel Injected!
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    ok, so added some grounds and still nothing. I had auto zone check the ignition module and they said it was good. I checked the pickup coil with my meter and it is appox 830 ohms which is within spec. according to my book. So I then decided to check the injectors by grounding the ground side wires. I could hear the solenoid click up so it seems to me that the injectors are sound. I next decided to hook up the gas to the inlet on the throttle body and then manually ground the injectors to see if they would spit some gas.. No GAS! I made sure the fuel pump was primed. Now Im really boggled. Now I'm thinking there is something wrong internally with the throttle body? Shouldn't it spits some gas if I manually ground the injectors Any ideas?

  11. #11
    Fuel Injected! jim_in_dorris's Avatar
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    First, undo the fuel inlet line and turn the key on for a second to start priming. Do you get fuel? Yes = look at fuel pressure regulator on tbi for plug. No = plugged fuel line. If plugged fuel line, remove fuel line before fuel filter and try again. If fuel pressent, replace fuel filter and start process over.
    Square body stepsides forever!!!

  12. #12
    Fuel Injected!
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    This is using about 6 feet of new fuel line going inot to a boat tank pm the side of my truck on a table as a temporary setup gpt testing. I was flowing gas directly out of the pump on a serperate test before I even hooked up the fuel pump to engine. The fuel pump is new also, the lines are new, and I even did a rebuild kit on the throttle body unit also before puting this engin in. I got a good pump 14 psi at 140GPH. Sames as the one we did before. Shouldnt the injectors blast some gas if I manually ground them out? And also shouldn't gas be flowing at that time? Thanks for your reply

  13. #13
    Fuel Injected! jim_in_dorris's Avatar
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    At 14psi, and 140 gph you should have fuel all over the place when you manually ground them, you have a problem in your throttle body somewhere. Do you have a lot of fuel coming out the return line?
    Square body stepsides forever!!!

  14. #14
    Fuel Injected!
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    the stock in tank fuel pump pressure is 14 pounds for this engine. So I believe I have the right size fuel pump. and its the same one we just did on a different engine. I will have to check the return line to see how much is flowing. The most fuel I got out was a few drips on a few tries. I agree at this point it may be some kind of plug within the throttle body. I just installed the rebuild kit, maybe did something wrong.. I don't know. I will tear it back apart tomorrow. Thanks Jim

  15. #15
    Fuel Injected!
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    also, gonna use some noid light testers on the injectors tomorrow to veryify they are getting pulse from ECM at start up. I am pretty sure they are at this point but thats just one more thing Im gonna check too.

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