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  1. #1

    Default 89 2500 Sub sputters & dies under load - 350 small block

    I dont know what has happened during my tune up.The motor will idle & rev in neutal all day, but when i put it in gear & go to accelerate it starts backfiring & will cut off sometimes.

    here's what I did this morning as a simple tune up:
    changed spark plugs to stock ACDELCO, same plugs that were in it.
    changed distributor cap & rotor, same cap & rotor style that were in it.
    changed spark plug wires, did one wire at a time to make sure I didn't mess up firing order.
    changed ignition coil to MSD ingnition coil
    changed air filter

    I've checked the firing order twice, it right.

    I dunno what the heck I did, any help is very much appreciated.

  2. #2


    Vaccum leak? brother-in-laws truck is a '96 chevy and his would do the same thing...found out it was a vaccum leak and all is good now!...just throwing that out there

    2009 Chevrolet Silverado 1500 LT Z71 Crew Cab "All-Star Edition"

    Line-X'd Bed
    Line-X'd Custom Brush Guard(Heavy Duty)
    5.3L Flex Fuel
    275/65R18 Toyo Open Country AT2's
    2" Rough Country Leveling Kit(want to get the 2.5 RC kit)
    EGR In-Channel Vent Visors
    Exterior PLUS Package
    Interior PLUS Package
    K&N Drop-In Air Filter
    Cat-Back Dual Exhaust
    Black Bowties
    Diablo Sport Predator(AFM Disabled)
    Towing Mirrors
    Next Planned Mods
    Blacked out Tail Lights
    Aftermarket Rims

  3. #3


    I'll check the vacuum lines again. Thanks.

  4. #4


    No, they all seem to have a good seal. As far as which hoses, I've checked all the hoses coming out of the throttle body.

  5. #5


    The problem may not be as severe as I originally listed. Sometimes the truck with back up the driveway, pull out the subdivision. But will start sputtering & backfiring when I get on the road. It seems to lose power & dies sometimes. I have to limp it back home sputtering & moving slow. I'm stumped...

    - - - Updated - - -

    Oh and I must add the truck ran ok before my tune up. I drove it an hour and a half from where I bought it without a problem prior to the tune up

  6. #6
    Sr. Engineer
    Join Date
    Oct 2010
    Indianapolis, In


    There are some combinations of miss wired plugs that will run and exhibit the symptoms you describe. There are aftermarket caps that look EXACTLY like stock but have an internal wiring scheme that allows the plug wires to be routed so that they do not cross over each other. Make sure the firing order matches the cap you have.
    2000 GMC YUKON SLT, 5.3L tow pkg, G80 rear/w 3.73 gear

  7. #7


    Guys, I'm an idiot. #2&#7 spark plug wires were backwards. How I missed this when I checked the firing order twice, I have no idea....

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