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Thread: Swapped a 2004 5.3. Can't get spark

  1. #1
    Join Date
    Apr 2015

    Swapped a 2004 5.3. Can't get spark

    I have swapped a 2004 5.3 with ecm and repinned the 5.7 harness to run the 411 ecm (Lextech pinouts) I have had a tuner come out and turn the vats off, new battery ext.... The efi tuner had communication with ecm but my scanner keeps telling me no communication. Any and all suggestions would be greatly appreciated. About to pull my hair out over here

  2. #2
    Join Date
    Aug 2014
    I hate problems like this! Very tough.

    First, you need to try a known good scanner. If the EFI tuner was able to communicate I can't think of any reason your scanner wouldn't, unless it's broken. Go back and forth between your vehicle and another with the same scanner. If it works on the other vehicle and not on yours repeatedly , that eliminates the scanner as a problem.

    If the scanner is good and it still can't communicate with your ECM, you either have a wiring problem or an ECM problem. Do you have a CEL operational? On your ALDL port, check for good power and ground. Listen to your fuel tank--you may need a stethoscope if you have a very quiet fuel pump. Have a helper turn on the ignition without trying the starter. Do you get the fuel pump running for 2 seconds? If not That's either wiring or the ECM or the fuel pump. Since you have no scanner comm, I'd guess it wouldn't be the fuel pump...

    You just have to be methodical and start ruling out different possibilities.

    Good luck!
    1992 K1500 Blazer.
    L94 & 6L80
    14 Bolt SF axle w/11" brakes & appropriate Combination brake valve, Eaton Trutrac rear posi.
    8000# hidden winch, Rocket Box, KYB Monomax shocks
    285/75R16 Duratracks
    Flat Panel Display Gauge cluster in progress.
    New interior & exterior paint planned.

  3. #3
    Join Date
    Jan 2012
    warwick ny
    Make sure all your grounds are connected. Usually is the cause of this problem.

  4. #4
    Join Date
    Apr 2015
    So when a cheap scanner is hooked up the cel illuminates and the truck fires up! But we definitely have a wiring problem, I'll be checking ground connection today after work thanks!

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