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Thread: Noob - help? - high IAC in drive, high idle until IAC retracts

  1. #1
    Fuel Injected! shimniok's Avatar
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    Noob - help? - high IAC in drive, high idle until IAC retracts

    I'm new at tuning so I have to beg for a little help :) I am just starting to tune the VE table(s) for my AMC 360 V8 equipped Jeep Grand Wagoneer with TF727 automatic trans. I'm using the $42 mask 7747 ECM, a bin that is very close to ASDU (let me know if it would help to attach it). I've checked the "Manual Transmission" flag. I'm using the V4T xdf and V4.2 adx files from here. I went through the procedure to reset the IAC (short AB, turn on key, wait a bit to make sure stepper motor closes off IAC, unplug IAC, turn off ignition, plug IAC). I've also set the idle screw stop to a point where I get around 20 IAC counts at idle. Base timing is set to 10*BTDC. I've done nothing to the timing tables.

    The current symptom I am seeing is that, during idle, in drive or reverse, the BLM numbers run around 145, and IAC counts increase slowly from idle, no-load value (presumably to compensate for rich mixture??). When I take it out of drive, idle races up to 2000rpm and it takes 30 seconds or so for the IAC to retract to permit normal idle again. I've attached a data log of what happens.

    The BLM count and IAC count suggest to me that I have a rich condition. Right? Is that the only issue?

    The park/neutral switch was disconnected, and I tried connecting it; it seems to have no effect on this particular behavior. Also, I mucked with an IAC scalar or two, but those didn't seem to change the behavior in any fashion. It was doing it before I mucked with 'em, was doing it after.

    Thanks,
    Michael
    Attached Files Attached Files
    1986 Jeep Grand Wagoneer - stock AMC 360 V8, 3" exhaust - 1227747 ECM - $42 ASDU - tc.wagoneer.org - www.bot-thoughts.com

  2. #2
    Fuel Injected! shimniok's Avatar
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    Answered my own question.

    According to the AutoProm manual (here) the innermost switch must be in the outboard position. In the innermost position, 160bps / 10K resistor across AB is selected, which puts the 7747 ECM in ALDL mode (I presume) and forces a 1000rpm idle.

    So what was happening is that in drive, the ECM was trying to achieve a 1000rpm idle by progressively increasing the IAC which didn't work because there was too much load on the engine (low stall torque converter) to ever reach 1000rpm using IAC alone.

    With the innermost AutoProm switch in the outboard position the symptom of increasing IAC while in Drive disappeared.

    Now, back to VE tuning...
    1986 Jeep Grand Wagoneer - stock AMC 360 V8, 3" exhaust - 1227747 ECM - $42 ASDU - tc.wagoneer.org - www.bot-thoughts.com

  3. #3
    EFI GearHead ! EagleMark's Avatar
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    Quote Originally Posted by shimniok View Post
    According to the AutoProm manual (here) the innermost switch must be in the outboard position. In the innermost position, 160bps / 10K resistor across AB is selected, which puts the 7747 ECM in ALDL mode (I presume) and forces a 1000rpm idle....
    Bingo!

    I've told Moates that and should maybe try again. But it's another internet rumor started before Moates, that has turned truth and we will be fighting it for years. 10K is not needed for most 160 baud ECMs.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  4. #4
    Fuel Injected! shimniok's Avatar
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    Quote Originally Posted by EagleMark View Post
    I've told Moates that and should maybe try again. But it's another internet rumor started before Moates, that has turned truth and we will be fighting it for years. 10K is not needed for most 160 baud ECMs.
    For what it's worth, Moates' documentation says that "some early ECMs" require the 10k, but that most everything will work on the non-10k position.
    1986 Jeep Grand Wagoneer - stock AMC 360 V8, 3" exhaust - 1227747 ECM - $42 ASDU - tc.wagoneer.org - www.bot-thoughts.com

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