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Thread: 1227747 to 16197427 Conversion PCM Swap with Wiring Pinout Directions!

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  1. #1
    Super Moderator dave w's Avatar
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    The '7747 is a 2K PPM VSS. The '427 is happy with a 2K PMM input to pin F13. The only time I needed 40 pulses / revolution was for an electronic overdrive transmission conversion.

    dave w

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    Quote Originally Posted by dave w View Post
    The '7747 is a 2K PPM VSS. The '427 is happy with a 2K PMM input to pin F13. The only time I needed 40 pulses / revolution was for an electronic overdrive transmission conversion.

    dave w
    What is the normal input from the VSSB to pin F13 on the '7427? Some sources say 2k PPM, but others say 4k PPM. And when do you need to set the "Output Speed not from DRAC" flag?
    Last edited by belaw; 08-13-2012 at 06:12 PM.

  3. #3
    Super Moderator dave w's Avatar
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    Quote Originally Posted by belaw View Post
    What is the normal input from the VSSB to pin F13 on the '7427? Some sources say 2k PPM, but others say 4k PPM. And when do you need to set the "Output Speed not from DRAC" flag?
    I've never measured the normal input to pin F13 from the VSSB. It seems to me, 2K is the expected input to pin F13 on the '427 PCM. I've only done the '427 PCM to vehicles that had either a '7747 / '8747 ECM's. As far as I know, the '7747 / '8747 have always been 2K VSS. I've never really noticed any difference when setting "Output Speed not from Drac" flag on the '427 PCM upgrades I've done. In the absense of "Factory Information" I've "Set" the "Output Speed not from Drac" on the '7747 / '8747 TBI PCM upgrades I've done.

    dave w

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    Fuel Injected! CDeeZ's Avatar
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    Quote Originally Posted by belaw View Post
    What is the normal input from the VSSB to pin F13 on the '7427? Some sources say 2k PPM, but others say 4k PPM. And when do you need to set the "Output Speed not from DRAC" flag?
    Brian,

    I think it depended on your original application. I believe 4K is the more common, but 2K is doable, and then check that flag "output sped not from DRAC"





    As far as the P/N switch: Since my C1500 was originally a 7747 ECM, it had a P/N switch on the end of the column, under the dash, inside the cab. When I still had the 7747 in there, I hooked up my laptop and when I unplugged the P/N switch entirely it showed as being in "Drive" all the time that way. (T-56 here BTW) I've left the P/N switch unplugged since swapping to the 7427.



    Quote Originally Posted by dave w
    The '7747 is a 2K PPM VSS. The '427 is happy with a 2K PMM input to pin F13. The only time I needed 40 pulses / revolution was for an electronic overdrive transmission conversion.

    dave w


    Dave, how exactly did you do the 2K PPM vs the 4K PPM???
    Last edited by CDeeZ; 08-13-2012 at 08:25 PM.

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    Super Moderator dave w's Avatar
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    Quote Originally Posted by CDeeZ View Post
    Dave, how exactly did you do the 2K PPM vs the 4K PPM???
    The VSS information from JTR, http://www.jagsthatrun.com/SpeedSensors_Order.html shows early Pickup TBI ('7747 / ' 8747) is 2K PPM.

    I've never tried to use the 4K PPM on a '427 PCM. The 4K PPM might work on the '427, but I don't have any personal experience doing so.

    dave w

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    Yes, 7747 applications expect 2k ppm. They were developed when the speedometer cable drove the speed sensor. I can cross check a 7427 wiring diagram against the DRAC outputs to determine speed signal frequency on F13. The "output speed not from DRAC" selection might be shown in the manual trans comparison thread currently running?

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    RIP EagleMark's Avatar
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    FYI DRAC on 1227747 and VSSB on 16197427 and they do not interchange.

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

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    Fuel Injected! JeepsAndGuns's Avatar
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    I know on mine, it did not read on the datalog dash untill I selected "vss not from drac". Once I did it started working. I am using the JTR 2ppm vss.
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 5 speed, 8.8 rear, homebrew hub conversion and big brakes, hydroboost, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

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