Newest Gallery Photos

  1. Chevy Truck Forum

    Welcome To!

    The #1 Chevy Truck Forum Online

    Online since 2004, we're the #1 Chevy Truck & SUV user community. If you have any questions about your Chevy or GMC Truck, SUV or Crossover, or just want to connect with other GM owners and enthusiasts around the world, you've found the best place on the internet to do that.

    Join Today ~ It's Free

    Registering is Free and Easy! Do it today and we'll see you on the forums soon!

Engine misfire

Discussion in 'Chevy C/K Truck Forum' started by gmcman101, Sep 8, 2008.

  1. gmcman101

    gmcman101 New Member

    I have a 1997 GMC (5.7) with a miss that I can't figure out. A friend of mine hooked his engine computer up and it says cylinder misfire. I could tell that by the way it runs. Changed the spark plugs checked the cap and rotor (look good) and it still runs terrible. It sounds like it's running on 6 or 7 cylinders. The engine shakes at all RPM's. Any suggestions on what I should check next?
  2. MrShorty

    MrShorty Epic Member Staff Member 5+ Years 1000 Posts

    Was the misfire code specific to a cylinder (P030x) or was it a generic misfire code (P0300)? If the misfire can be isolated to a specific cylinder that might help narrow down the diagnosis to things specific to that cylinder.

    Did the change the wires when you changed the plugs? If not, any sign of a bad wire (spark leak or high too high resistance)?

    I've heard of a few cases where the distributor gear wears funny, creating ignition problems. If you are careful so you can get the distributor back in right, it might be worth the effort to pull it and check the gear.

    Fuel delivery up to spec (fuel pressure up to spec, all "injectors" firing)? I know our vintage 5.7's have issues with the stock poppet valves, to the point that GM has redesigned the injector spider to use real injectors. I'm not familiar with the diagnostic procedure, but it may be worth looking into.
  3. dwill3015

    dwill3015 Epic Member 5+ Years ROTM Winner 1000 Posts

    I'm not sure on the 97's but my experience with the misfres on the Vortec engines has mostly been a result of a bad coil pack (on misfiring cylinder).
  4. gmcman101

    gmcman101 New Member

    I thought of a coil pack too, until I started getting into it and found that it has a coil.
    It must of been a generic misfire code because it didn't tell which cylinder was not working.
    As far as injectors not firing, it think it has a throttle body. The truck ran good one day and the next day it just ran the way it does now. Bad. Thanks for your replies.
  5. Calbaby968

    Calbaby968 Rockstar 100 Posts

    Did you try a compression test on all the cylinders?
  6. dwill3015

    dwill3015 Epic Member 5+ Years ROTM Winner 1000 Posts

    I had to replace a bad coilpack on our 2001 suburban because of a random mis-fire code that kept coming back even efter replacing the plugs and wires so I thought it was worth a shot. You could check for intake manifold leaks to see if it might be a vacume problem. Fuel filter maybe?
  7. gmcman101

    gmcman101 New Member

    No, I didn't do a compression test or check for vacuum leaks. As far as the fuel filter, that was changed about a year ago and I can't afford to buy parts it don't need. Thanks for the replies, I was hoping it might have been a common problem that I didn't know about and someone would say check your...
  8. gmcman101

    gmcman101 New Member

    OK, let try this question. I was told by a friend of mine that it does have injectors and they are located under the intake. One for each cylinder, is this true? I was told by another friend that it only has one injector that runs to all the cylinders? Which is true? Does anyone have a picture of a intake that removed? Thanks again.
  9. MrShorty

    MrShorty Epic Member Staff Member 5+ Years 1000 Posts

    You have 8 "injectors". The guy who says only one is probably confusing your '97 with the TBI setup that was used on '95 and older 5.7's. They are inside the intake. If you end up replacing them, you'll want to get the newer, upgraded spider that uses real injectors instead of "poppet" valves.
  10. gmcman101

    gmcman101 New Member

    Thanks MrShorty, thats sounds like a lot of work. So the guy at the parts store will know what I'm talking about when I tell him I need the upgraded version? Do I need a Central Port Injector Assmembly? Not sure what to ask for.
    Last edited: Sep 16, 2008

Share This Page