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misfiring help

Discussion in 'General Chevy & GM Tech Questions' started by reggiecab2000, Nov 10, 2011.

  1. reggiecab2000

    reggiecab2000 Rockstar 4 Years 500 Posts

    hey guys,
    my truck has been misfiring for about 2 months now and i cant figure it out,
    i just had it at a mechanic yesterday and thought my problems were solved, family friend mechanic so i know hes not screwin me, he pulled out the ignition control module and tested it and it was bad. popped in a new one and problems are still there...
    i have 2 new crankshaft position sensors in the last 6 months, new cap, rotor, plugs, wires, fuel filter, fuel pressure is good etc. i have a strong feeling it is something electrical due to a DTC (U1255) for a class 2 communication malfunction. if you ned more info and think you can help please let me know, this is a very bothersome problem for me..
  2. TRPLXL2

    TRPLXL2 Epic Member 5+ Years 1000 Posts Platinum Contributor

    Anytime you get a code beginning with U, your not going to be able to get a true diagnosis without a tech 2 unfortunately. What I would do is track down another computer for your truck, they're all over ebay for $75. Your ICM might not have been bad, the ECM controls all of the spark tables and it can do funny things. Basically a class 2 fault is a grounding issue, meaning there is a short somewhere in the engine harness.
  3. reggiecab2000

    reggiecab2000 Rockstar 4 Years 500 Posts

    Thanks for your input.
    also i just installed some stainless steel braided brake cables on friday in the front and (im sure this has nothing to do with it) didnt get to finish bleeding my brakes entirely, still spongy. drove it around it to feel the brakes did its normal (noticeable to me on the inside) misfiring came back parked in front of my garage and had to leave to go to a formal. then the next morning had to go to san antonio for a marathon, came back sunday night, woke up monday morning for work and my truck wont start...
    cranking, cranking, cranking had to leave in our back up CR-V.
    came home same thing but i got it to start a few times
    horribly rough idle, shaking, vibrating when pushing the accelerator, and dies randomly, in no condition to drive...
    any help for that? or do you think this may be all due to the ECM?
    this is frustrating...
    Last edited: Nov 14, 2011
  4. TRPLXL2

    TRPLXL2 Epic Member 5+ Years 1000 Posts Platinum Contributor

    Well there is a free test you can do that is about 50% reliable on the ecm, since there is no difinitive way to check an ecm 100% other than replacement. Take a 1/4" drive extension and tap on the top of the ecm lightly while the truck is stumbling and messing up, If it changes in any way then the ecm is bad. I got this tip off of my firebird club, It actually lead me to find out my ecm was bad before I spent a lot of money on nothing. Worth a shot....
  5. reggiecab2000

    reggiecab2000 Rockstar 4 Years 500 Posts

    sounds like an easy test... is the ecm the box beside the battery?
  6. ippielb

    ippielb Epic Member 5+ Years ROTM Winner 1000 Posts

    It is right below the battery, it is positioned angled towards the engine. Pop the plastic cover off and it is plugged in with two vertical plugs.
  7. reggiecab2000

    reggiecab2000 Rockstar 4 Years 500 Posts

    i believe that is the box i was referring to, i just re read my post and i look dumb it looks like i was referring to the fuse box lol but i think i meant the same as you, that angled weird shaped one. ill give it a few taps and see what happens...

    ---------- Post added at 03:01 PM ---------- Previous post was at 02:19 PM ----------

    okay so i tapped all over the ecm, jiggled all 4 of the connections, tapped all over the maf sensor wire, any and almost all other sensors i could see engine related, and pulled and tugged on as many wires as i could, and nothing.... it still only starts up when it feels like it, but anything on the accelerator and the whole truck starts shaking, horrible misfiring...
  8. TRPLXL2

    TRPLXL2 Epic Member 5+ Years 1000 Posts Platinum Contributor

    Well that sucks that it didn't work...

    I don't know what else to say now, that would be something I would have to see. Hopefully someone else can shed some light into this. Sorry I couldn't help more..
  9. reggiecab2000

    reggiecab2000 Rockstar 4 Years 500 Posts

    okay so my truck still has its on and off days on starting but once its started it idles just fine, anything over 1000 rpms and there goes that earthquake feeling, why does it not do it at idle but at any point on the gas?
  10. reggiecab2000

    reggiecab2000 Rockstar 4 Years 500 Posts

    UPDATE! and i really need some input on this guys...
    took my truck to chevy this morning and they ran a diagnostic with their tech 2 ...
    sooo my distributor is bad and i also have a leak from some coolant in my intake manifold (which ive known for a while now not a big leak)
    but they said for the distributor:
    parts labor blah blah
    for distributor and fixing the leak (which involves removing intake manifold and new gasket and new fuel pressure regulator)

    I know that the dealership charges high prices but can someone please let me know asap if this is ridiculously high or if it is comparable
    THANK YOU!!!

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