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Thread: 5.3 misfires, can't find the problem!

  1. #1
    Join Date
    Jan 2012
    Posts
    13

    5.3 misfires, can't find the problem!

    I just bought my 99 Silverado Z71 RCLB, 5.3L, automatic. Has 155k on her, and I think she's had a real hard life. I replaced the plugs and wires as well as running sea foam through the intake and feul to clean it up. Cyl 4 is misfiring consitantly and the oil pressure is unusually high, like 60 psi @ 2k rpms. Oil is mobil 1 high mileage less than 1k old.

    Any suggestions would be greatly appreciated, I am fairly handy and would love to fix this myself. My buddy told me seafoam may have eaten the piston rings, is this a possibility?

    I swapped plugs and wires and the misfire did not move, I plan to swap coils next. Thanks!

  2. #2
    Join Date
    Jan 2012
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    13
    also, previous owner was more of a dog person, he got rid of his cats.

  3. #3
    Join Date
    Aug 2007
    Location
    Honeywood, Ontario
    Posts
    7,112
    Could be a lean misfire. Could be a coil, swap with another cylinder. Never once have I heard of Seafoam damaging rings, and it's pretty damn hard to screw that process up enough that you'd cause damage.
    2006 Silverado
    Little Black Bitch

  4. #4
    Join Date
    Mar 2010
    Location
    Paris, TX
    Posts
    511
    Swap the coils 4x6 to see if the miss moves to 6. If that doesn't work swap the injectors 4x6. However, a compression test would be a good check also.

    Never heard of sea-foam damaging rings, plugs yes but not rings.
    99' Silverado RCSB Z71: 5.7L Iron LS1, 11.2:1, Custom EPS Cam, Ported 862's,Ported TB, E-Bay Cold Air, E-Bay Long Tubes, Dynomax X-Pipe Exhaust, Electric Fans, Innovative LC-1, Self Built 4L60E, Circle D Pro Single Disc, 4:10 ValueTrac


    http://www.ls1truck.com/forums/image.php?type=sigpic&userid=7887&dateline=1270435  715

  5. #5
    Join Date
    Apr 2006
    Location
    Bellevue, Nebraska
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    check the coils by removing the boot at the coil and see if it arcs. If you get a good arc, it's not the coils. Maybe post a sound clip of if from under the hood.

  6. #6
    Join Date
    Nov 2009
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    SAN ANTONE
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    perform a compression test, inspect for broken valve springs, use noid to be sure injector is pulsing
    06 rcsb, 6two, 231/235, 4.11, pacesetter, 80e, 14 bolt, Nelson tuned
    2011 rcsb 6two swap in the works with 6l90 and boost
    FARMTRUC CAN GARGLE PEANUT BUTTER

  7. #7
    Join Date
    Jan 2012
    Posts
    13
    Wow! You guys are a heck of a lot more helpful than the gto forums! No one told me to take it to the dealer! Will swap coils tomorrow and see how that works out.

    Did more intake manifold cleaning tonight, burned off alot of carbon, still misfiring though. Thanks for the support on seafoam, ididnt tbink itwould cause sucha problem!

  8. #8
    Join Date
    Nov 2011
    Location
    Arlington, Tx
    Posts
    416
    What casting heads does it have?
    PERFORMANCE-TUNING-FABRICATION
    12617 FM 917
    Alvarado, TX 76009

  9. #9
    Join Date
    Jan 2012
    Posts
    13
    Quote Originally Posted by Ray@NP View Post
    perform a compression test, inspect for broken valve springs, use noid to be sure injector is pulsing
    Ray, what do you mean by a noid? I very much appreciate your time!

  10. #10
    Join Date
    May 2008
    Location
    Crowder, OK
    Posts
    8,064
    Quote Originally Posted by LSXPS View Post
    What casting heads does it have?
    Castech 706s and a crack on cyl 4?

    Possible.

    1969 Chevy RCLB C10 350/TH400 SOLD
    2007 Chevy RCSB 4.8 4x4 LS SOLD
    2008 Chevy RCSB 5.3 4x4 LT SOLD
    2010 Chevy CCSB 6.2 4x4 LT SOLD
    2005 GMC CCLB DRW 6.6 Duramax 4x4 191,000 and counting
    2013 FORD CCSB F350 6.7 Powerstroke 4x4


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