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Thread: Weak Injector Pulse

  1. #1
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    Weak Injector Pulse

    Hello all,
    On my 95 GMC K1500 350 Auto TBI, the driver side injector is not spraying as well as the other and has a weak ground signal coming from the ECM to fire it. I swapped the injector connectors and it follows the one injector harness. The green wire coming out of the ECM for the Ground Signal is week at the ECM plug. I have taken some ground straps off of the fire wall and frame rail in engine compartment to clean up and no difference. Anybody have any other ideas? I have also tried unplugging the TPS sensor wire for whatever reason that I read on other forums that I have been researching. I have seen where other people have had the exact problem but there is never a conclusion to the problem. IF I need a new ECM is there a way to convert it into a ECM that I can put a EBL into it?

    Thanks,

    R.S.

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    Fuel Injected! PJG1173's Avatar
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    have you checked resistance on the wire between the injector and computer?
    87 4Runner, 15" spring lift, 3" body, chevy vortec 355, 5.29 gears, 38.5x15.5x15" Boggers, 280hr, 16168625 running $0D
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    Quote Originally Posted by PJG1173 View Post
    have you checked resistance on the wire between the injector and computer?
    Well, I checked and it showed that there were no breaks in the wire. I don't think there should be resistance should there be?
    I got the same dim test light when cycling at the ECM as at the injector harness.

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    If the wire is good, you might have an ECM that's going bad. Do you have one you can swap out to see what happens?
    1973 K-5 Blazer, TBI 350, TH400, 1 ton axles & 38" SSRs'
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    Quote Originally Posted by fastacton View Post
    If the wire is good, you might have an ECM that's going bad. Do you have one you can swap out to see what happens?

    I do have another ECM out of another 95. It does not have the same Prom ID # though. I tried it before and it didn't seem to make any difference.
    Makes me think that there is a problem somewhere that supplies the ECM. I suppose I could have picked up a bad ECM at the yard as well...

    Thanks,

  6. #6
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    Quote Originally Posted by Rally Smith View Post
    Well, I checked and it showed that there were no breaks in the wire. I don't think there should be resistance should there be?
    I got the same dim test light when cycling at the ECM as at the injector harness.
    there will be some resistance. since you are getting a signal to the injector it is assumed that there are no breaks in the wire. I wouldn't just check for continuity, if you compare resistance of the good injector's wire between the computer and injector to the one you are getting a weak signal on you can rule out the wire itself. also have you tested voltage on the B+ side of the injector?
    87 4Runner, 15" spring lift, 3" body, chevy vortec 355, 5.29 gears, 38.5x15.5x15" Boggers, 280hr, 16168625 running $0D
    93 S10, 36x12.5x15 TSL's, custom turbo headers, 266HR cam, p&p vortec heads, $0D Marine MPFI with 8psi boost.
    05 Silverado, 2' lift, 4" exhaust, Bully Dog programmer,

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    Quote Originally Posted by PJG1173 View Post
    there will be some resistance. since you are getting a signal to the injector it is assumed that there are no breaks in the wire. I wouldn't just check for continuity, if you compare resistance of the good injector's wire between the computer and injector to the one you are getting a weak signal on you can rule out the wire itself. also have you tested voltage on the B+ side of the injector?
    I have checked the positive side of the injector harness on both sides and they are the same. (12v) Not sure that will make a difference because I can see the weak signal at the ECM Plug. Not sure if I can attach a short video or not but I'm going to try to show the issue I see.

    Thanks,

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    Put down the test light it shouldn't be used for testing anything Efi forget you own it unless it's an Efi specific led version or a noid light for testing injector drives.unplug injectors and ecu and battery test resistance of the 12v feed from injector power relay to both injectors separately.then test resistance of the feeds from injectors to ecu

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    I can't upload it. It's a .mov file and that won't work. Basically what it shows is, at the ECM the Negative (pulse) wire going to each injector. I have a 12v test light hooked to the battery positive and the light end stabbed into the ECM plug where the pulse wire is coming out of. On the "good" driver side wire when cranking shows a bright light pulse going to injector. Then I do the same with the other injector pulse wire. It shows a very weak (dim) pulse when cranking. Looks the same at the injector as they do at the plug.

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    delcowizzid:
    I will give that a shot and let you know what I find.

    Thanks,

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    Quote Originally Posted by delcowizzid View Post
    Put down the test light it shouldn't be used for testing anything Efi forget you own it unless it's an Efi specific led version or a noid light for testing injector drives.unplug injectors and ecu and battery test resistance of the 12v feed from injector power relay to both injectors separately.then test resistance of the feeds from injectors to ecu
    ^X2 get a decent digital multi meter.
    87 4Runner, 15" spring lift, 3" body, chevy vortec 355, 5.29 gears, 38.5x15.5x15" Boggers, 280hr, 16168625 running $0D
    93 S10, 36x12.5x15 TSL's, custom turbo headers, 266HR cam, p&p vortec heads, $0D Marine MPFI with 8psi boost.
    05 Silverado, 2' lift, 4" exhaust, Bully Dog programmer,

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    Haven't checked resistance in wires just yet but I hooked up my laptop since I'm getting SES light now. Shows I have an Ignition Failure (code 42).
    If I'm not mistaken the voltage for the injectors come off of the ignition. Will do some more checking and get back.

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    If you live near a harbor freight you can find a coupon online for a free dvom. Thats what i do every time i break the leads on my dvom. I have two hf dvom's without leads because they always twist off at the end. They seem to work fine. Never had a bad reading. http://www.dealsoff.com/images/free_...exp.4-9-15.jpg

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    Harbor Freight DVOM?
    89 K1500 Scottsdale 5.7L 5spd 3:42 RamJet cam Dart iron TBI heads 427 PCM swap
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    Quote Originally Posted by brian617 View Post
    Harbor Freight DVOM?
    I had one threw it away...
    87 4Runner, 15" spring lift, 3" body, chevy vortec 355, 5.29 gears, 38.5x15.5x15" Boggers, 280hr, 16168625 running $0D
    93 S10, 36x12.5x15 TSL's, custom turbo headers, 266HR cam, p&p vortec heads, $0D Marine MPFI with 8psi boost.
    05 Silverado, 2' lift, 4" exhaust, Bully Dog programmer,

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