Hit a big bump, now a misfire??? help please?

Discussion in 'GM Powertrain' started by silvertrd, Jul 19, 2010.

  1. silvertrd

    silvertrd New Member

    i took a trip to buy a part off craigslist for my truck 85 miles away, ran great to the guys house which was a ranch so when i turned onto his dirt road i hit a bad bump and my truck started stumbling/hesitating and misfiring when continuing on the road uphill. when i started my journey home, still stumbling. driving down the freeway cruising at 2k rpm when it misfires revs drops to around 800 then pick back up instantly, misfires randomly. definately worse under load it seems. got off the freeway to find a parts store(not sure what i was going to buy btw) and the truck died at a stoplight. started backup after a few tries. never found a parts store(was in B.F.E.) so i decided to limp it home. as luck should have it, a car almost hit me badly so i swirved hard and the problem went away so i got on the freeway and all drove perfect for about an hour until the freeway got bumpy, then the problem came back. fuel gauge jumps around hard when it stumbles but only %20 of the time. gauge also already has that annoying vibration dance so dont know if this is a symptom or not.

    truck has new plugs, wires, air filter, cleaned tb and had fi cleaner ran thru it about 1k ago.

    thats about where i'm at now, please help.


  2. ippielb

    ippielb Epic Member 5+ Years ROTM Winner 1000 Posts

    What year is your truck? Would be nice to have a little more information on your truck, to be able to try and help.
  3. Mean_Green_95

    Mean_Green_95 Epic Member 5+ Years 1000 Posts

    Possibly the knock sensor(s) have gone out or the bump you hit register the knock sensors.
  4. silvertrd

    silvertrd New Member

    its a 99 gmc sierra 2500 5.7L with 200k

    do u think the knock sensor wires could just be loose? and where is it so i can check if they are indeed loose.

    also, might there be any stored codes even though the cel never came on?

    that question reminded me that the abs light came on when i was having this problem, but all is well with the brake system AFAIK other than needing pads.
    Last edited: Jul 20, 2010
  5. NastyZ28

    NastyZ28 New Member

    Stupid idea - unplug and reseat your plug wires. 1 at a time... all of them, both ends.
    My #5 plug wire likes to fall off the #5 plug. Eyeballing this is obvious when the plug is laying there. Yours may look like they're plugged in - but not seated. It'll usually work but may not always work. A visual inspection will further confuse the situation. Pull them off and reseat them. Then see what happens.
  6. silvertrd

    silvertrd New Member

    driving around today the problem got a lot worse and the truck left me stranded, seemed to get better once the truck cooled down so i limped it home. it finally threw on the cel so im gonna get a code reader now to hopefully point me in the right direction. however, after much reading on this forum and others, this may be a pretty vague help. but its worth a shot.

    ---------- Post added at 03:10 PM ---------- Previous post was at 01:29 PM ----------

    bought a code reader for 50 bucks at harbor freight and apparrently it was money well spent. it pulled code p0339 crankshaft position sensor A circuit intermittent.
    then i drove the truck and it was perfect again, no matter how hard i got on it, but i didnt let it get hot like stop and go does. i'll keep you guys posted. thanks
  7. Mean_Green_95

    Mean_Green_95 Epic Member 5+ Years 1000 Posts

    Well at least it is an easy fix, or at least I think it is.
  8. silvertrd

    silvertrd New Member

    well it was an easy fix to change the crank position sensor but unfortunately it didn't fix the problem. that was also the only code that was thrown, bummer. now i dont know where to look next. it just bugs me that a misfire this bad isnt triggering any codes and the misfire readout on the obd2 reader comes in clean....super confusing.

    any ideas?
  9. Mean_Green_95

    Mean_Green_95 Epic Member 5+ Years 1000 Posts

    Go ahead and check the timing if you haven't already. After that, maybe try sea-foaming your vacuum lines to see if that clears anything up.
  10. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    Also take a look at your cap and rotor. It is kinda looking like you need to take a look at the dist shaft and see how much play it has from side to side, checking to make sure the bushings arent shot. Also I would take a look at your plugs, checking for a too lean or too rich plug indicating a possible bad injector/ regulator. I would also mabey try a Sweep test on the TPS since when you hit the bump you might have knocked something.. Also try cleaning your MAF there is a cleaner for it since there might have been some dust in the intake that got by your Filter and caused you to get it on the MAF.
    And try some seafoam just to make sure some internal carbon didnt get into something it wasnt supposed to. Oh and when was the last time it had a fuel filter? There might have been something that got by the pump and clogged it as well.

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