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Thread: 5.7/700R4, high idle and stumbling. Log attached

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  1. #1
    Fuel Injected!
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    5.7/700R4, high idle and stumbling. Log attached

    Folks-

    I have what we'll call a 1989 Chevy K1500 with TBI 5.7L V8, 700R4 automatic transmission (because it's actually in an 89 S10, but I digress..)

    ECM is a 1227747, running factory code. Definition file for Tunerpro was EagleMark's $42-1227747-V5.2

    I am experiencing high idle (around 12-1300 RPM), stumbling at speed, and although I do have a good bit of torque it still feels like it's down on power.

    I datalogged a recent drive, and have the following observations:

    -TPS Volt is way out of range- 0.14V at idle, and IIRC about .4 volts at heavy throttle

    -IAC counts may be out of range as well- I'm still learning this stuff

    -Temp seems fine, at 194deg at speed and 199 at idle (ambient temp was about 75)

    -Vacuum is ranging from about 19 at idle, to an indicated -6 on heavy throttle. I believe I saw somewhere that a negative indication before the integer actually indicates positive pressure.

    -I messed around under the hood looking for a vacuum leak, finding none. I did find the vacuum reservoir had a hose that had dropped onto a manifold and melted in two. Can not find where that is supposed to go, however. I haven't found any vacuum hoses "adrift" in the engine bay. Only thing that has a loose hose is the cruise control servo and the trans vent. This bears further investigation, that reservoir used to go somewhere, I need to find it. However, given that I have 19 inches of vac at idle I'm thinking it can't be much of a leak.

    -While chasing down the above with engine off, I had my hands pretty much on everything. Afterwards, I cranked and it was idling at about 800RPM. I applied the throttle and let go, and idle would not go below 1100. I almost wonder if this is indicative of a throttle cable with too much stiction- it's 30 years old, maybe it just needs to be replaced like the TV cable on the trans was?

    -I pulled codes. 22, 32, 33, and 45. I see that as:
    22- TPS Signal low (um, duh, knew that! :) )
    32-MAP sensor signal open or EGR Error (I have the EGR vac port capped off both at the TBI and the solenoid)
    33- MAP Sensor Signal error (signal high indicating low vacuum)
    45- OX sensor error (rich indication)

    The Injectors, fuel pressure regulator, and associated gaskets are brand new. The O2 sensor is brand new. The TPS is likely near 30 years old. The MAP sensor is not known to fail, typically.

    Being that the TPS is most suspect and demonstrably bad, I plan on replacing it first. The other problems may be cascading false positives from that (and the fact the EGR is capped off)

    I have a log file, will attach it to this thread for inspection.
    Last edited by 89S10_Project; 09-10-2016 at 02:24 AM.
    -Phil, in Charleston, SC

    '89 S10 Blazer: SOA SAS: Dana 44s, 5.7L V8, 700R4; 35s, 4.10:1; TBI with 1227747 ECM
    '94 Grand Cherokee: 4.0, 4" lift, 31s
    '90 Jeep Cherokee: In progress: 5.7L V8,700R4,NP231C, D44s. TBI with 1227747 ECM
    '87 Fiero GT: 3.8SC (initial research stage)

  2. #2
    Fuel Injected!
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    Leaving a bit of a trail to IAC troubleshooting for myself and others as I keep thinking this might be part of it:

    http://www.gearhead-efi.com/Fuel-Inj...-testing/page3
    -Phil, in Charleston, SC

    '89 S10 Blazer: SOA SAS: Dana 44s, 5.7L V8, 700R4; 35s, 4.10:1; TBI with 1227747 ECM
    '94 Grand Cherokee: 4.0, 4" lift, 31s
    '90 Jeep Cherokee: In progress: 5.7L V8,700R4,NP231C, D44s. TBI with 1227747 ECM
    '87 Fiero GT: 3.8SC (initial research stage)

  3. #3
    Fuel Injected!
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    Tulsa, Ok
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    If this is a transplant,triple check your grounds. But looking at the TPS voltage, it's definitely got issues. Clear DTC's, unplug the TPS, turn key off, push pedal from closed to full throttle and back to closed. wait 3 seconds turn key to run position then recheck TPS voltage. If TPS is still out of whack, get a volt meter set to DC volts and check grounds between the TPS, engine block, battery, and body. TPS will have 3 wires. 5volt DC reference voltage. Ground. and Signal return. If all these items check out, replace the TPS.

    Buddrow
    If it don't fit force it, if it don't force fit f&%@ it!

  4. #4
    Fuel Injected!
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    I think if you look at the wiring diagram, you should see that those sensors share a ground that, on the full size C/K tucks is attached to a stud on the thermostat housing. Are you using the v6 or v8 harness? Also, how is your MAP sensor attached vacuum-wise? Should not be any troughs or loops if at all possible and closer to the port(shortest vacuum hose possible) is best, usually at the center, rear of the throttle body.
    If it don't fit force it, if it don't force fit f&%@ it!

  5. #5
    Fuel Injected!
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    Answering the questions posed:

    All of my grounds are via 4 gauge wire, soldered to ring terminals, and go from battery to frame, battery to block, block to block (at each side of the intake manifold, as well as from driver's front to back of the intake, and from driver's back of manifold to the body as well as driver's block forward side of manifold to frame. (Yes, I'm kinda ground-paranoid).

    That said, I abandoned the thermostat housing stud ground as that's always irritated me when it comes time to service the cooling system. I can't imagine how the aluminum intake would be not grounded, what with 3 of the bolts holding it down having grounds attached with star washers, but I will check just to make sure and maybe run a ground wire to the boss that formerly held the coil (although in all honesty, it's already explicitly grounded by the strap at the throttle bracket, but ok). Not being grounded at that exact point the factory used doesn't matter, especially as I've massively upgraded the conductivity of the grounds.

    Don't know what "clear DTC" means.... will GTS.. :)

    This is a transplant into an 89 S10 Blazer. It originally had the 4.3 and auto trans. The TBI harness is compatible between the two engines. I am using the computer that came with the engine, it was a plug-and-play operation.

    One thing to note- I don't have the "idle-up on crank" that I had with the 4.3. As they use the same TBI arrangement I would expect that to be applicable here as well. Some quick research tells me this points to the IAC.

    MAP sensor is attached to the factory port on the front of the TBI, I replaced the fragile and broken hard vac line with similarly (ID) sized fuel hose (I always do this as it's much more durable and I hate chasing vac leaks). It's the minimum length necessary to enable nice bend radius , and is within 20% +/- of the factory hard hose length.

    Now that you mention the center rear of the TBI, I hav to admit I may have an open port there. But how on earth could I have that and still have 19" of vac at idle?
    Last edited by 89S10_Project; 09-10-2016 at 03:26 PM.
    -Phil, in Charleston, SC

    '89 S10 Blazer: SOA SAS: Dana 44s, 5.7L V8, 700R4; 35s, 4.10:1; TBI with 1227747 ECM
    '94 Grand Cherokee: 4.0, 4" lift, 31s
    '90 Jeep Cherokee: In progress: 5.7L V8,700R4,NP231C, D44s. TBI with 1227747 ECM
    '87 Fiero GT: 3.8SC (initial research stage)

  6. #6
    Fuel Injected! sturgillbd's Avatar
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    DTC = Diagnostic Trouble Code Check engine light is on. Clear the codes by removing battery terminal for 30 seconds or so. I agree with buddrow. Check the grounds and connections for the sensor grounds. Sensor ground from the ecm has to have a good electrical connection to the engine block and battery ground. Map sensor should be connected to the port on the back of the TBI. See the first post in this thread: http://www.gearhead-efi.com/Fuel-Inj...n-vacuum-ports

    Brian

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