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Thread: I'm stumped...truck no worky.

  1. #1
    Fuel Injected!
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    I'm stumped...truck no worky.

    Alright guys, I'm completely stumped by this and need some help figuring it out...

    I replaced the intake manifold recently on my 1995 K1500 and everything went back together fine, BUT my injectors are not firing and I cannot connect to the PCM nor can I pull codes via the paperclip trick...no idea if these separate issues are related at all.
    I swapped out ignition modules since I had an extra module laying around and no luck. I also pulled the dizzy and installed a new AC Delco pickup coil and turned the distributor with a drill while I checked coil output with a multimeter to make sure it was working properly, all good there and still the injectors refused to fire.
    I checked both ecm fuses in the underhood fuse block...the fuses are good.
    I checked all PCM grounds for continuity...grounds are good.
    I jumped the injectors with 12v and the injectors are functioning properly.
    I swapped in another PCM and still no luck(this is NOT a known good PCM).
    I checked input voltage at the PCM with key on and am getting good voltage to the PCM.
    Thinking that maybe my chip got smoked somehow, I burned a brand new chip and...nothing.
    I've checked and rechecked that all sensors are properly connected.
    Fuel pressure is good and pump primes as it should with key on.

    I did swap to a 454 throttle body and rewired the IAC and TPS while I was doing the intake. I just matched wire colors when wiring in the flat TPS connector...did I wire it wrong maybe? I did unplug the TPS connector and tried to fire it just in case that was the issue and still no luck.

    Perhaps I should test this TPS for proper function...I'm grasping at straws here though. What did I screw up?? The truck ran before I tore it apart, although I was experiencing a strange high/hanging idle and I think this issue happened before I replaced the intake because the truck wouldn't start the last couple times I tried to fire it up before removing the intake.

    Thoughts?
    95 ecsb vortec 357 10.44:1 scr LT4 hot cam single plane TBI 7427 $0D

  2. #2
    Fuel Injected! pmkls1's Avatar
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    What does the CEL do when you turn the ignition on ? Does it come on steady, or flash continuously, or not come on at all ? It sounds like a memcal issue maybe, but that is just a SWAG at this point. The behavior of the CEL sometimes gives a clue to what's going on.
    1999 GMC Sierra 1500 standard cab long bed 4.8 V8 2WD - A work in progress.
    2000 Grand Prix GT sedan 3800 - My new daily driver inherited from the wife via the insurance company totaling it out after a minor collision.
    2006 Grand Prix GT sedan 3800 Supercharged - The wife's new grocery getter.

  3. #3
    Fuel Injected!
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    CEL stays solid, no rapid flashing that usually points to a bad PROM. It also stays constantly on instead of flashing when I jump the A and B terminals at the ALDL connector.
    95 ecsb vortec 357 10.44:1 scr LT4 hot cam single plane TBI 7427 $0D

  4. #4
    Fuel Injected! pmkls1's Avatar
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    Well, I don't have much at this point I'm afraid. I would definitely try to focus on communicating with the PCM though. It sounds like for whatever reason the PCM isn't really functioning but the fact that the fuel pump primes is odd. I would suggest checking for power to all of the junctions and fuse blocks aside from the ignition inputs to the PCM. Another question would be does the truck have VATS ?
    1999 GMC Sierra 1500 standard cab long bed 4.8 V8 2WD - A work in progress.
    2000 Grand Prix GT sedan 3800 - My new daily driver inherited from the wife via the insurance company totaling it out after a minor collision.
    2006 Grand Prix GT sedan 3800 Supercharged - The wife's new grocery getter.

  5. #5
    Fuel Injected!
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    No, VATS is not enabled in my bin. I thought that if the fuel pump is priming properly then that would point to a functioning PCM, but why can't I pull codes?...very odd indeed. I'm lost. Something got hosed and I can't figure out what it is.
    95 ecsb vortec 357 10.44:1 scr LT4 hot cam single plane TBI 7427 $0D

  6. #6
    Fuel Injected!
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    Do you have vRef?
    (reference voltage....5V to your TPS)

  7. #7
    RIP EagleMark's Avatar
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    CEL should come on, blink, then stay on solid.

    If you have power to PCM, did you check fuses? There's another one for injectors...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  8. #8
    Fuel Injected!
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    Chevmasta, I haven't checked for ref voltage at the TPS. I'll do that tomorrow after work...

    Mark, I checked the ECM fuses in the under hood fuse block, is there another fuse for the injectors other than those?
    CEL does as you describe, but won't blink in sequence to pull codes...??
    95 ecsb vortec 357 10.44:1 scr LT4 hot cam single plane TBI 7427 $0D

  9. #9
    RIP EagleMark's Avatar
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    I'm not sure it will blink codes that PCM?

    Hook up to TunerPRo and see what codes are set.

    Do you have spark? Are fuel injectors pulsing?

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

  10. #10
    Fuel Injected!
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    It will blink codes, I've pulled codes with a paper clip before...no dice anymore though.

    Tunerpro will not connect although the cable is found and functional.

    I haven't tested for spark and no, I don't think the injectors are firing at all; the throttle bores are completely dry even after extended cranking.
    95 ecsb vortec 357 10.44:1 scr LT4 hot cam single plane TBI 7427 $0D

  11. #11
    RIP EagleMark's Avatar
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    No spark = No DRP = no injector pulse.

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

  12. #12
    RIP EagleMark's Avatar
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    In the $OE thread is some good wiring diagrams, but in $0D thread is pinout diagrams with key on volatge check. Something is wrong. Even if you chip was bad it should run.
    http://www.gearhead-efi.com/Fuel-Inj...Information-OD

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

  13. #13
    Fuel Injected!
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    I checked pickup coil output before I installed the dizzy so I know I'm getting DRP...I'll see if I can get someone to give me a hand so I can check for spark tomorrow.

    I did try two different ignition modules though and one was known good, yeah I'm running out of ideas...fuhhhhh!!!
    95 ecsb vortec 357 10.44:1 scr LT4 hot cam single plane TBI 7427 $0D

  14. #14
    Fuel Injected!
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    I'm pretty sure I have a good grasp of how the ignition system works on a TBI system...what am I missing? I know I have a good ignition module and a good pickup coil, what else is there? I'm getting 12v to the injectors, I know they're functional...I'm getting frustrated.
    Something that probably doesn't matter, but I've been wondering about...I relocated the ignition coil to the fire wall, does the coil need to be grounded to the engine to work?
    95 ecsb vortec 357 10.44:1 scr LT4 hot cam single plane TBI 7427 $0D

  15. #15
    Fuel Injected! jim_in_dorris's Avatar
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    Do you have access to a noid light? Check for pulses at the injectors. If you are getting pulses, you have a fuel delivery problem. I would suspect the fuel pressure regulator in that case. Fisrt check for pulses at the injectors. not fuel, electrical. The ecm should be driving them to ground.

    I reread your first post, are you saying that when you jumper the injectors directly they spray fuel?

    Big block IAC's are wired differently, but I don't think that would stop fuel delivery.
    Look at voltage out at TPS. is it around .45 volts KOEO not touching the throttle?
    That also should not stop fuel.
    The startup for fuel comes from the distributor and doesn't switch to drp until it starts. I have to agree that it is a wire you are overlooking
    Last edited by jim_in_dorris; 03-04-2013 at 10:57 AM.
    Square body stepsides forever!!!

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