GM Truck Club
THE PREMIER CHEVY TRUCK & SUV FORUM
Founded in 2004 ~ We're the #1 Chevy Truck & SUV Forum.
Silverado & Sierra | Tahoe & Yukon | Suburban & Yukon XL | SUV & CROSSOVER
Results 1 to 9 of 9
  1. #1

    Default need ideas on a missfire problem

    I got a 87 1/2 with the tbi 350. A couple weeks ago i put on a different set of heads I bought off a friend and the truck ran just fine. on Xmas eve on my way to work I noticed the truck started to develop a missfire. As the day went on the missfire became worse. After work I put on new wires and a coil but it didnt make a difference. The truck has a rough idle and when driving down the road it struggles to run. While it was sitting and idling I noticed the every few minutes it was making a load popping noise and spitting fire from between the manifold and the exhaust pipe on the drivers side which leadds me to believe the missfire is on that side. I just went and pulled the valve cover off to look at the pushrods to see if maybe one was bent but they look fine. Later today I am going to start it up and watch the rockers as it runs to see if I have a collapsed lifter or even worse, sheared a lobe off the cam. If you have anymore thoughts on the matter please let me know.

  2. #2
    Master Mechanic TexasEdition's Avatar
    Join Date
    Dec 2010
    Location
    Texas Hill Country
    Posts
    656

    Default

    Check the exhaust manifold gasket on that side. Also check to see if any bolts are loose on the new install. Open the hood and press the throttle and listen closely for ticking or clicking sound when you accelerate. I always say go back to the last thing you did and retrace your tracks first. Since you installed new headers, your engine might be running too rich now if you significantly opened airflow.

  3. #3
    Sr. Engineer
    Join Date
    Oct 2010
    Location
    Indianapolis, In
    Posts
    493

    Default

    May be a vacume leak. Hopefuly just a loose hose at best and at the worst an intake gasket. Try some spray cleaner around the intake and TBI and see if there is a change in how it runs, this would indicate a leak. Is this a steady or consistant miss?
    2000 GMC YUKON SLT, 5.3L tow pkg, G80 rear/w 3.73 gear

  4. #4

    Default

    this sounds to me more like the timing has slipped some. Make sure your dist is still tight and double check your timing. Also check the obvious, vacuum lines, etc. If no leaks and timing is good, you possibly have a dist going bad or computer. When you start getting backfires and missfires, it's usually timing related.
    1986 Chevy G20 Tow Rig - 5.7 TBI conversion
    1978 Mustang II King Cobra Road Racer - Holley 650, MSD 6AL, 5 speed, 10 point Roll Cage, 9" posi, fuel cell, custom interior.

  5. #5
    Sr. Apprentice Looey's Avatar
    Join Date
    Aug 2009
    Location
    London, Ontario
    Posts
    74

    Default

    Could also be a head gasket. Check for any signs of coolant in the crankcase. It will show up on the dipstick and the underside of the rocker covers as a white milky substance. Did you use a non re-torquing head gasket, or a steel shim head gasket? Either way, if you can re-torque the head bolts it would't hurt.

  6. #6

    Default

    Quote Originally Posted by TexasEdition View Post
    Check the exhaust manifold gasket on that side. Also check to see if any bolts are loose on the new install. Open the hood and press the throttle and listen closely for ticking or clicking sound when you accelerate. I always say go back to the last thing you did and retrace your tracks first. Since you installed new headers, your engine might be running too rich now if you significantly opened airflow.
    Actually, headers and the increased airflow tends to make engines run LEAN. In theory, the PCM should be able to adjust the fuel ratio based on O2 sensor data.

    I would pull the plugs and see if any are green from coolant or black from oil.
    Last edited by 2COR517; 01-02-2011 at 10:46 AM.
    When you hear hoofbeats, look for horses not zebras.

  7. #7

    Default

    Is the vehicle blowing out white smoke upon starting the vehicle? If so it is a pretty good indicator you have a head gasket leak and are burning antifreeze and water. I would probably agree more with DualDJ on this one though... It sounds like a timing/ distributor problem to me as well. When you said you replaced your coil, are you talking about the pick-up coil in your distributor? Also would try a cap and rotor as well if so. My '90 350 tbi did this to me and the cap and rotor fixed the problem.

  8. #8
    Legend
    stephan's Avatar
    Join Date
    Sep 2010
    Location
    Far West, Oregon USA,
    Posts
    8,610
    Blog Entries
    1

    Default

    Hey BD, check that your #5 & #7 wires are not running too close alongside each other. They can crossfire when they are close together & will cause it to fire when the exhaust valve is still open on #5 & light off the unburned fuel in the exhaust pipe. You also need to keep #8 & #4 far apart on the other side.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  9. #9

    Default

    what condition were the heads in, it could possibly be a bad valve. I do agree with dpeter though, i would ckeck for intake leaks, and bad vaccume lines and rule out all other simple solutions before i pulled the heads.
    Keith Webb Sr.:mdr:
    1999 silverado 2500
    1989 k-5
    1982 c-10

Similar Threads

  1. Replies: 3
    Last: 12-22-2010, 08:38 AM
  2. 98 Silverado 5.7 Liter bad missfire under load
    By lightemup in forum GM Powertrain
    Replies: 2
    Last: 12-21-2010, 07:56 AM
  3. any ideas on mp3
    By cobra2end in forum Audio, Video & Gadget Tech
    Replies: 12
    Last: 05-30-2010, 02:40 AM
  4. 4L60E Problem Any Ideas?
    By Duramax04 in forum General Chevy & GM Tech Questions
    Replies: 4
    Last: 02-02-2010, 10:09 AM
  5. 2001 tahoe rough idle/missfire
    By bracebldrs in forum Chevy Tahoe Forum (GMC Yukon, Cadillac Escalade)
    Replies: 3
    Last: 01-25-2007, 11:56 AM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •