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  1. #1
    Sr. Apprentice
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    Default No injector pulse?

    Been a member for a while but haven't posted much...I've been doing the mother of all rebuilds. Sorry for no posts but I took lots of pics and will post extensively.

    Sadly par for the course? Major issues at new motor fire attempt.

    89 gmc 4x4 2500 sub. 91 replacement motor rebuilt and new cam. Used all original electronics and tbi. New wires, plugs, cap, rotor, fuel filter,etc...
    have spark, have fuel at the back of the tbi. No pulse at all from either injector? This thing ran when I parked it to work on it. Checked fuses inside @ fuse inside...don't have the money to just start buyingc electronics until it works. Wondering if anyone has an idea? Already read several accounts online but all had no spark or no fuel or tried changing things from factory. Mine is 100% original and worked when parked? WTF?

    ---------- Post added at 03:30 PM ---------- Previous post was at 01:53 PM ----------

    I pulled the four pin connector from the dist. all I have is a standard radioshack volt meter. Purple/white wire with key on had barely any signal at all. Wires to the injectors have 12v with key on. I have fuel at the rear of the tbi but not sure of the pressure? No pulse whatsoever.

    ---------- Post added at 05:09 PM ---------- Previous post was at 03:30 PM ----------

    I am left to assume the fuel pump which I can hear run and never had an issue with before...now has not enough pressure for no reason at all? Or an electrical part failed while not being used? Both are perfectly reasonable? Right?
    Last edited by TMAL1; 03-12-2012 at 04:06 PM.

  2. #2
    Sr. Engineer
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    Dec 2011
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    11-22-boogie woogie avenue
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    Default

    Okay ecm fires injectors with ground...should have a set of ground wires at thermostat..and one on intake behind where ac pump is or should be.
    Make sure clean and connected tight. Two other things work with firing injectors ..pickup coil..and ignition module.
    Make sure you did not miss something a wire loose connection when you put all back.
    Can you prime it will run for a few seconds?

  3. #3
    Sr. Apprentice
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    Auburn, ca
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    Default

    i have a major ground wire from intake to the firewall by the ac/heater box. It is good. As it is a brand new engine? I didnt want to pour gas in and temp fire it. It needs a break in
    Id like to test the ignition module. Can I do it with a simple volt/ohm meter? Thanks for the help.

  4. #4

    Default

    If you can find a diagram for the ign module that shows what "good" ohm between pins on the plug would be you can check it vs what you're actually reading. Im not too keen on TBI injection systems personally... but do you know where exactly your injector pulse is supposed to come from?

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  5. #5
    Sr. Engineer
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    Default

    I guess no one reads....injector pulse comes from ecm..via ignition module..pickup coil.Once ecm senses 400 rpm,s from engine it takes over.
    But injectors pulse works off of ground from ecm...you have to have the grounds at thermostat and intake or will not pulse injectors.Grounds for all sensors.
    Can not test ign.module with a meter..due to heat variances .
    Can take to auto parts to test. Have a machine that heats it up to certain temp.
    Now you can ohm out the pickup coil on dist. shaft....disconnect green &yellow wire from ign. module
    Set meter to ohm,s probe green wire with one lead from meter yel. with other ..should get 700 to 1200 ohm,s of resistance.

  6. #6
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    Default

    Wow...not sure about the ground wires near the thermostat being that repainted it all. Could be poorly grounded. Will check in the morning. Thanks. That makes more sense than anything else.

  7. #7
    Sr. Apprentice
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    Auburn, ca
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    Default

    Sadly...all grounds are excellent. Have pressure. Module tested out fine. Battery grounded directly to motor. Unplugged tps and nothing. Repeated with all sensors. No pulse at all. Again...12v at each pod. All wires look fine.
    Last edited by TMAL1; 03-13-2012 at 06:58 PM.

  8. #8
    Sr. Apprentice
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    Default

    I guess I'm on my own.

  9. #9
    Sr. Engineer
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    Default

    If it ran before ..you must be missing something..wire a connection..has to be either a bad ground..ign. module. pickup coil ..bad or clogged injectors
    Or bad ecm.
    RESIDENT NUT.....MY CLAIM TO FAME .....

  10. #10
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    Default

    Bad module? Tested out fine.
    Bad coil pick up? With spark?
    bad ecm? With spark, 12v to each pod, 12v to coil? If with all these factors the ecm could be bad? If so I would like to know if the ecm controls none of these.
    With fuel pressure, 12v to each pod, 12v to coil, good ignition module, spark seen on a timing light, motor grounded to block, two good and checked grounds...can the ecm be bad with virtually everything working seeking flawlessly? Both injectors suddenly clogged or died simultaneously while sitting on the garage floor?

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