Question 1987 GMC V2500 Sierra Classic Code 44 Lean Fix?

Discussion in 'Classic GM' started by Earl Phillips, May 18, 2017.

  1. Earl Phillips

    Earl Phillips New Member

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    This truck just had the motor replaced with new GM crate motor 5.7ltr in OCT2016. As a note: the idle surging problem existed prior to this writing and I had replaced numerous parts to no avail. Garages told my problem prior to replacing motor was an either a internal vacuum leak and needed to replace my intake manifold gaskets or water pump etc. None of those repairs helped. Since a bearing went on the bottom end and the motor needed to be replaced, I thought this would solve my issue with surging idle. After three weeks at a dealer, checking and or replacing numerous parts they determined they could not fix it. They turned up the idle screw and gave up. In my effort to help myself, I replaced the vacuum booster but that did not make a difference in the idle fluctuations. In 6 months I have 700 miles on the new motor and recently I notice a momentarily hesitation and then the check engine light came on. Code 34 & 44. Dealer told me to check for a vacuum leak. I did look and could not find any cracked hoses or lines that are not connected. I plugged the vacuum line that even feeds the vacuum pots for the heater controls, nothing changed. Looking for suggestions that could possible be the culprit other than the obvious ie: IAC, TPS, TBI & gaskets, Injectors, EGR, MAP sensor, Charcoal Canisters, Vacuum Booster, fuel pressure, fuel tanks, fuel pumps, dry or brittle vacuum lines, vacuum ball reservoir. Thanks...
     
  2. Art61

    Art61 New Member

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    I would recheck the airgap for the idle and find a procedure for Iac reset just in case they missed something i'm not sure what year your truck is I'm hoping it's in the 90s
     
  3. Art61

    Art61 New Member

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  4. Art61

    Art61 New Member

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  5. Art61

    Art61 New Member

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  6. Art61

    Art61 New Member

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  7. Art61

    Art61 New Member

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  8. Art61

    Art61 New Member

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  9. Art61

    Art61 New Member

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  10. Earl Phillips

    Earl Phillips New Member

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    The truck is a 1987 v2500 Sierra Classic, 5.7 ltr TBI. I checked the truck today and the only code it is show is 12 and 44. I just don't know where else to look for a vacuum leak. When it was at the dealership they had tested fuel pressure was within the limits.
     
  11. Art61

    Art61 New Member

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    Code 12 the system OK they all start that , it's a system check mine does it too I feel for you I have a brand-new crate engine too 3 Gm mechanics can't figure out the problem I would check for exhaust leaks and the O2 sensor according to the book
    Good luck
     
  12. Art61

    Art61 New Member

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    You pretty much need a OBD one scanner to work on these things like a tech one or a tech two or a snap on
     
  13. Earl Phillips

    Earl Phillips New Member

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    Thanks Art... I printed out those pages, thank you. I would have thought the Chevy Dealerships mechanics would have performed these procedures at that time. As a novice in comparison to the combined mechanical abilities and knowledge base of the certified mechanics, I am to say the least a bit flabbergasted. Thanks again...
     
  14. Art61

    Art61 New Member

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    No problem I hope it helps I bought those GM manuals for my 95 but it's basically the same stuff few changes but not much
     
  15. Earl Phillips

    Earl Phillips New Member

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    This is a follow-up to the lean mix code of the 1987 GMC 5.7Ltr Sierra Classic 4x4. A quick back story.. after the 2nd motor in 1993, (about 3-4 years later) a surging idle started. After many different opinions by auto mechanics over many years, none where truly on target. The 3rd motor (10/2016) was to resolve all the issues but did not. That surging idle came back with a vengeance and stumped the GM garage that installed the new GM crate motor. I had it towed to a GMC dealership who said they could fix it and after one day said the could not... had it towed back to a local garage who promised me they could fix it. After four hours of testing the following occurred: 1. disconnected the air pump. 2. disconnected the EGR solenoid. 3. Reset the timing (it was way off) 4. smoked the motor. 5. replaced the MAP sensor as it would not hold a vacuum.

    Now the idle would hold fairly steady between 600-800 rpm. A week later the wild idle surge came back and would stall and idle from 425 to 800. Back to garage and now the mechanic put the MAP sensor in default mode. The idle is holding reasonably steady and he now feels some this wrong with the MAP circuit.


    As of 07-31-2017
     
  16. -Cuba-

    -Cuba- GMFS Member

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    This makes me believe that there could be an issue with the harness or ECM then... all 3 engines having the same issue? The only thing they didn't change, or it's not common to replace without a specific reason such as cooked looms, is the harness... However this should have been "pinned out" to verify the integrity of the harness, especially after 2nd engine swap & having the SAME condition.

    Don't replace the ECM without knowing for sure the harness is OK because this can fry the new ECM & you're back in the same boat. Wiggle the harness while testing for its integrity, because there could be broken wires inside the insulation causing somewhat erratic conditions or intermittent at times. This is my 2 cents.... but does this make sense? You didn't mention the specific components that were replaced. I'm just assuming, knowing how most techs work
     
  17. Earl Phillips

    Earl Phillips New Member

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    Cuba, thanks for the reply. This was an update to a previous post. The MAP sensor was replaced as indicated as it would not hold a vacuum so I am told. The first motor did not have this issue. The failure of that motor was a clutch fan which failed and cooked the motor. The second motor experienced the idle surge issues about 4 years or so after the installation. When I worked on it in the mid to late 1990's, I replaced the EGR, IAC, TPS, temp sensor, rebuilt TBI with new injectors. At that time I did not replace the MAP sensor. It was not perfect but seemed to settle out but was led in different directions by various mechanics. Since then, I replaced both fuel tanks, sensors and fuel gauge along with saddle frame straps. This last motor install was a complete package from JEGs which included a new holly intake. They put in new injectors and replaced the TBI as they thought the throttle place was seeping air, allegedly swapped out other parts temporarily but did not make a difference. In the end, they tweaked the idle up and advanced the timing and sent me on my way. Many other new parts but not part of the idle surge issue.
     
  18. -Cuba-

    -Cuba- GMFS Member

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    Interesting! Thanks for going into depth. I'm sorry I didn't realize there was another thread. I also overlooked the years in between the last 2 repairs. Your issues have certainly piqued my interest. I see that now you were just swapping out parts "temporarily" too. I took it to mean "throwing parts at it" as many untrained mechanics like to do in hopes that one will stick and fix it all, while leaving the customer broke & frustrated.

    Also upon reviewing your answerr, I didn't notice how far back this was posted. But from what I'm understanding now, you are still having the issue just masked for now by tweaking the idle & timing. Thank again for taking the time to post your response!
     
  19. Earl Phillips

    Earl Phillips New Member

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    Cuba.. The mechanic stated he set the timing and idle to spec's for the 5.7ltr motor. What's at issue is the MAP sensor circuit or so he thinks as he replaced the MAP sensor. As it is in default mode, the trucks runs fairly well but not one hundred percent. I would of thought he would have checked the plug end for corrosion or breakage or maybe a misaligned connector pin. I have the truck home as I needed it back so the next step in this costly process of elimination is to let the mechanic check the wiring harness for any issues.
     

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