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intermediate firing injector (TBI 350)

Discussion in 'The Garage' started by gimmie11s, Jan 2, 2006.

  1. gimmie11s

    gimmie11s Registered Member

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    Hello all-

    vehicle is 91 Chevy suburban 2500 4x4 w/350.

    I just bought this truck and it runs intermittently good then bad. its driving me crazy. basically driver side injector fires all the time and seems to be fine. Passenger side injector does NOT fire at idle at all. passenger side injector DOES fire when applying the throttle but the spray is so powerful when it comes on that it floods and stalls the motor. The thing runs so pig rich its making my eyes bleed. The question is 1) SHOULD both injectors fire in an identical fashion all the time? 2) Why would one injector fire seemingly "when it wants to" causing the erratic performance.

    I have swapped pigtails and when this is done, the oppossitte injector has the problem. This leads me to beleive that both injectors are FINE and the problem lies in the ECM which is telling the injector to act irratically.

    I have replaced plugs, o2 sensor, rebuilt the throttle body (this went well) with all new gaskets, o-rings, and fuel pressure diaphram.

    The previous owner said it has a remanufactured NAPA ECM in it. In pulling the ECM, i have verified this. The ECM is, however, just lying in its compartment behind the glove box NOT bolted down.... does it need to be?


    any help would be GREAT!

    thanks-
     
  2. diesel4me

    diesel4me 1 ton status Premium Member

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    A few things to check..

    It might be the wiring itself at fault..those wires get pinched between the throttle body and the air cleaner on many GM vehicles..I see lots of them all squished,and replacing them will restore proper funtion..most of the time!..

    Also,the ignition module controls the firing of the injectors,as well as the spark..I see lots of them fail intermittently..sometimes it takes DAYS before it acts up again..

    I recently helped a friend with an 86 C30,that was stalling out,and would have no fuel at the injectors.(truck had a newer EFI 350,and an ECM,and all the wiring swapped over,from an 87 donor truck..).it just had a new fuel pump,tank ,and sending unit, and ignition module installed at another shop..the owner THOUGHT it was fixed,but 2 days later,it died again..

    When we went to tow it to the shop,it started right up when we tried it!--so I just followed him with the wrecker,in case it died again..we let it run almost an hour before it quit again,and it wouldn't start back up..we thought maybe the pick up coil in the HEI was bad,but the owner said he had the other shop install a rebuilt distibutor before the fuel pump,hoping that was the problem..and it was only a few months old..so we assumed that wasn't the problem...

    After an hour passed,it started right up when we tried it..my friend climbed under the dash and started wiggling wires..as he did this,he noticed the computer was just tucked up under the glove box,with "zip ties" securing it to the other wires..he tapped on the case,and it shut the motor off momentarily!...AHA!!

    All along it was the computer not being grounded,as far as we can tell....after opening the ECM case to make sure the "prom" hadn't fallen out or was loose,we added a ground wire from the case of the ECM to the body,and it hasn't acted up once in 2 weeks yet,and the owner claims it has more power than it ever has...might be part of your problem too??..:confused: :crazy:
     
  3. gimmie11s

    gimmie11s Registered Member

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    Hmmm.. thats definitely something else i'll look into. Im pretty sure that the wiring is ok though, as i cannot find any pinches or detached wires.

    thanks!

    -dd
     
  4. gimmie11s

    gimmie11s Registered Member

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    any other ideas???

    TIA
     
  5. gimmie11s

    gimmie11s Registered Member

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    Well, through my searching threads on this board, ive come up with a couple of different things it could be.

    dist module
    pick up coil
    temp sensor?
    inj fuse
    bad ecm (inj driver)

    ill go through these and see what i can come up with

    thanks-
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    Only ones of those that I would even begin to think might be probable causes are the injector drivers (ECM) or the injector fuse, but the fuse seems highly unlikely as well.

    All those other components "feed" data to the ECM, so if it was a problem with the components you mentioned, it would either end up being inconsistent problems, or consistent with both injectors. Since you have one injector alone that is the only problem, I'd focus on things that can affect only one injector...ECM, power feeds, bad injector and wiring. I can't think of anything else that would cause one injector to be problematic. You've already eliminated the injectors themselves as the problem.
     
  7. gimmie11s

    gimmie11s Registered Member

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    very true and thank you.

    i solved the problem yesterday and it ended up being a bad ECM....

    i yanked my chip, swapped in a new ECM, and BAM.... it is running so good im ear to ear grins...

    thanks again

    -dd
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    Glad to hear you got it fixed!

    The injector drivers in the GM ECM's, at least 80's stuff, seem to be a pretty common failure, as "rare" as failures are for ECM's that are right around 15 years old! :)
     

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