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Truck running like crap!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by njonl, Jul 18, 2006.

  1. njonl

    njonl 1/2 ton status

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    I can't seem to figure out why it's running so bad.. I just recently replaced the heads and since then, it's done nothing but give me trouble. It seems to only do it when it's warmed up. I hop on the freeway to go to work and it runs fine. Just about when the temp hits 190 degrees, it starts to stumble and hesitate. I got off the freeway at my exit and it seemed to idle fine when at the stop light.. After taking off from the stoplight, it started coughing and hesitating real bad almost as though it is loading up. I put it in neutral and clear it out a little bit and then it runs fine for a minute or two, then it's back to coughing and hesitating. Here is the list of things I have replaced: Fuel filter, spark plugs, MAP sensor, and the pickup coil. I checked all the vacuum connections and everything seems to be ok. It seems to be really intermitent and it's driving me nuts! Any help you guys can give would be great. Thanks,

    -Nick
     
  2. 1985_K5_Silverado

    1985_K5_Silverado 1/2 ton status

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    Is the ECM tossing out any trouble codes?
     
  3. njonl

    njonl 1/2 ton status

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    Nope.. Not a single code
     
  4. onetonbb74

    onetonbb74 1/2 ton status

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    try fuel pump, if not sounds like vapor lock is the fuel line near the exhaust system at all. If its running lean, the exhaust gets 2x hotter and could cause a fuel pressure drop and sometimes it takes a tank of gas for the computer to throw a code.
     
  5. Thunder

    Thunder 3/4 ton status

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    Distributor module
     
  6. njonl

    njonl 1/2 ton status

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    Would the distributor module cause this kind of stumbling and backfiring ? I think I am going to take it in tomorrow and have someone scan the computer. It's driving me nuts and it's my daily driver...
     
  7. Thunder

    Thunder 3/4 ton status

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    Yes its pretty common for the dist mod to start acting up when they get hot. You can pull the dist mod and take it down to AZ or napa they can test it for you.
     
  8. njonl

    njonl 1/2 ton status

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    Had the distributor module tested at Napa.. They tested it a few times and it passed every time. Any other ideas ? I'm seriously lost now.
     
  9. njonl

    njonl 1/2 ton status

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    So I took the truck in today to a shop.. He put a scanner on it and said it was doing all kinds of weird things throwing a bunch of codes and then the computer would acutally shut off and then turn back on again. He said I need a new computer. What do I do from here ? Where do I find a new computer ? Any info you guys can give me would be great. Thanks!
     
  10. njonl

    njonl 1/2 ton status

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    Replaced the ECM with an ECM from a junkyard.. Still having problems though. It was only $50 and they said it was guaranteed to work otherwise I could bring it back. Anybody have any input ?
     
  11. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    What's the CTS history?
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

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    Yeah, get a new mechanic. Blaming the ECM off the bat is a sure sign of a hack mechanic.

    Sorry if he's a friend or something, but I'm sick of seeing these "pro's" continually do this. Something like 95% of all ECM's replaced aren't even bad when they are sent to actually be rebuilt.

    First take a glimpse at all the wiring you can get to...make sure nothing is cut, disconnected, etc.

    It sounds to me like something going on while in closed loop. I'd check out your O2 sensor. It's common for the non-heated ones to drop out of closed loop while idling, and they aren't closed loop while cold, so it running good cold (open loop, O2 sensor not used to determine fuel) or at idle really seems to point towards an O2 problem. You can check that multiple ways, or just replace it *with a Delco* if it's old. I hate the throw parts at it mentality, but if you'd rather not spend the time, get a Delco O2 sensor and put it on there. If it's not bad, you're out what, maybe $80, but you know that's good for another 100K or so. If you so desire.

    Going WOT while it's acting up can be an indication as well, if it runs good with the pedal down under pretty much all conditions, I'd be inclined to believe it's not an ignition issue.

    A scanner (autozone used to let you borrow them for free) will let you get a glimpse at a few sensors that you would be best to check for correct operation...O2, TPS, MAP, and coolant temp sensor.
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    Oh, and as an aside, the ECM losing power kills the engine. Where's the smilie with the stupidest look on it...:angry1::hack:(that one is labeled hack lol):screwy::shame::mad1::surepal::mad:
     
  14. njonl

    njonl 1/2 ton status

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    Thanks for the replies guys.. I have replaced the o2 sensor just a week ago but that doesnt mean its working correctly I'm assuming. I have also replaced the coolant temp sensor, map sensor, EGR solenoid, fuel filter, cap, rotor, wires, pick-up coil, spark plugs, EGR valve is fairly new, had the ignition module tested, and I replaced the computer. Taking it to another shop today and the guy is supposed to be a hot shot with computers so we will see. I kind of thought telling me the ECM was bad seemed like an easy way out.. Thanks again for your replies
     
  15. dyeager535

    dyeager535 1 ton status Premium Member

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    And also, I do NOT trust the tests you have done on the modules or any electrical components (starters, batteries, etc) I've been told my battery was good (it wasn't) and I've seen many others with bad modules that tested good on the bench, whichdoesn't simulate heat or vibration experienced on a vehicle..

    FYI, spring for GM modules and O2 sensors, those two are NOTORIOUS for being bad out of the box when aftermarket. (not saying replace what you have, but you've got two suspect components right there)
     
    Last edited: Aug 1, 2006
  16. Thunder

    Thunder 3/4 ton status

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    So what trouble codes are you getting?
     
  17. njonl

    njonl 1/2 ton status

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    I am tired of dealing with this so I went ahead and bought a new ignition module.. It seemed to solve the problem a little bit to where it still does it but just not as often. As far as trouble codes go, when I try and pull the codes out, it is not giving me any at all except for the standard code number 12. I am not using a scanner, I am using a piece of wire as a "jumper" cable. Taking it to a shop in the morning. The guy there is supposed to be some wizard with computer systems. We will see...
     
  18. njonl

    njonl 1/2 ton status

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    Ok well... hundreds of dollars later, I find out that it is a loose ground to the intake manifold. Apparently that ground strap grounds just about everything so it is rather important.. Simple fix. Thanks for everyones input. I appreciate it
     
  19. jamber2541

    jamber2541 1/2 ton status

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    where exactly is the ground strap located ( where does it ground from) I have been experiencing the same problem and I cant find any ground straps on my intake manifold
     
  20. njonl

    njonl 1/2 ton status

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    I'll have a look on my lunch break and get back to you
     

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