Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Engine Backfire HELP!!!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by cityfarmer2, Apr 4, 2000.

  1. cityfarmer2

    cityfarmer2 Guest

    Guys got a call from a fellow K-5 owner. He has a 85 with 305 and 4 speed manual. He has been experiencing backfire and missing with rough idle for the first 10 minutes after startup after that all ops normal. He is traveling 4 hours just to come see me for help. Talked to him on the phone asked everything I could about carb, timing, fuel and air mixture, plugs, plugwires, distributor, vacume leaks, exhaust leaks, valve setup, and expected a lot of I don't knows but this man has been through everything. Three different carbs new plugs ,plug wires and timing chain with all possible advances test to move the curve with no favorable results. Problem started after a clutch replacement but all expert knowledge says just coencidental. Need some Ideas. I still say choke or valve although the only real experince is working with Holley, his is a Quadrejet. Any help would be appreciated. I just hope this guy isn't wasting his time when he gets here. I can't believe it only runs this way when its cold. Thanks Gary...
     
  2. Logan

    Logan Registered Member

    Joined:
    Feb 17, 2000
    Posts:
    93
    Likes Received:
    0
    Location:
    Fournier, Ontario, Canada
    When you figure it out, let me know! I've got an 84 with the 305 & 4speed that's doing the same thing, with the addition of one small thing: I can't push down on the gas more than 1" when it's cold (Anywhere near freezing), otherwise the engine bogs down so hard that you can actually hear the rear wheels sqwak -- just like I was standing on the brakes for a split second.

    I've been through timing, all vac lines look okay, there's no binding in any of the carb linkages, I've put water remover, carb cleaner....everything.

    I figured it was just time to do a carb rebuild -- I got the truck in November from a guy who did all his own maintenace since the truck was new, and he'd never touched the carb. Hehehe, the cloud of smoke that *filled* the Canadian Tire parking lot when I can a can of carb cleaner through it can attest to that. ;)

    Let me know what you find!

    -Al.
     
  3. BlueKnight

    BlueKnight 1/2 ton status

    Joined:
    Mar 6, 2000
    Posts:
    1,518
    Likes Received:
    0
    Location:
    Oregon
    Well you either have a lean condition or raw fuel is entering the exhaust and igniting. Is it back firing through the carb or through the exhaust? also look at the plugs. If they are this clayish light brown coated color you may have a stuck valve,burnt valve, or stuck lifter. Also how old is the cam??? Chevy's are known for flattening cams and that would throw everything off
     
  4. 85blaze

    85blaze 1/2 ton status

    Joined:
    Feb 20, 2000
    Posts:
    117
    Likes Received:
    0
    Location:
    Corning NY
    Hey, I will let you know an answer about how to fix it as soon as I talk to the crew I am working with, GM has some sort of backfire control on that model year, disconnect it and your set! TTYL

    Blaze On ----- into the $$$ pit! Dang these things can cost ya alot!
     
  5. Eagle86K5

    Eagle86K5 1/2 ton status

    Joined:
    Mar 5, 2000
    Posts:
    974
    Likes Received:
    0
    Location:
    Whitehouse, Ohio
    My 86 did not like the cold weather till I replaced the tube that ran from the exhaust manifold to the air cleaner and replaced all the vacuume lines.Now it runs fine cold or not.

    <font color=green>Eagle86K5[​IMG]

    <font color=red>Only guy I know that can get out of line in a one car funeral
     
  6. Shawn

    Shawn 1/2 ton status Premium Member Author

    Joined:
    Feb 17, 2000
    Posts:
    1,753
    Likes Received:
    5
    Location:
    5280'
    I had this same problem one time after I replaced everything (carb, plugs, wires, dist/cap/rotor, etc). My cam was flat on several lobes. Take the valve covers off and look at the rockers to make sure they are opening the valves all the way. If not it's cam time... Good luck.


    Shawn
    <font color=blue>87 K5</font color=blue>
    <font color=red>454, 6", D60, 14 blt, 465, 205</font color=red>
    www.off-road.com
     
  7. White Knight

    White Knight 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    889
    Likes Received:
    0
    Location:
    Ft Worth,Texas
    One other place to check is the accelarator pump, good Luck....may the dirt raise to meet you and the wind be always at your back..White Knight
     
  8. Blazer79

    Blazer79 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    1,816
    Likes Received:
    0
    Location:
    Guatemala, Central America
    If its so bad you hear the tires, maybe you should check the timing chain. Another idea is that one of the vacuum valves on the carb may have gone bad, so test them with a source of vacuum and see if they move whatever linkage they are attached to. Did you change spark plugs and wires? Did you check inside the cap and the rotor?

    Just a few ideas to see if I could be some help.

    <font color=black>//////
    What the heck!...Drive it like gas is $0.50/gal!!!
    </font color=black>[​IMG]
     
  9. cityfarmer2

    cityfarmer2 Guest

    Well guys started working on the guys truck for about six hours. Was completely dumb-founded for almost five hours. Determined from the get go that it was not choke or carb related. Checked timing was dead nuts. Started looking at the exhaust for leaks. Carb loaded up and backfired through the exhaust sounded like a cannon going off. I almost hurt myself justgetting out from under there. Well too the distributer out and did a detail inspection and swapped in new module and disconnected the harness from firewall and bingo running great. Will let you know how it starts in the morning. Gary...
     

Share This Page