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

  1. #31
    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

  2. #32
    EFI GearHead ! EagleMark's Avatar
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    Quote Originally Posted by dave w View Post
    The challenge I see to using a '427 PCM without a VSS is being able program which Spark / Fuel tables (Near Idle / Off Idle) for the PCM to use. I'm thinking without a VSS input, the '427 PCM will always think the vehicle speed is ZERO MPH. The '427 PCM could be programmed to switch from near idle / off idle, Spark / Fuel tables by TPS% only? I've never tried using TPS% only programming on the '427.

    dave w
    I've done this and is working quite well. I did it because someone elsewhere said it could not be done. That said I will never do it again to save $80 for a VSS... way to many hours tuning to work out bugs...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  3. #33
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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 08:12 AM.

  4. #34
    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

  5. #35
    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 10:25 AM.

  6. #36
    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

  7. #37
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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?

  8. #38
    EFI GearHead ! 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!
    -= =-

  9. #39
    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.

  10. #40
    Quote Originally Posted by JeepsAndGuns View Post
    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.
    X2.

    (Extra letters because X2 is simply too short.)
    Familiar with 1227747 and 16197427 PCMs

  11. #41
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    VSSB is a type of DRAC. Original reprogramming docs didn't even say "VSSB". All my data shows the "white box" versions are plug compatible but if you have something different I've got an open mind. Earlier trucks had DRAC built into the back of the dash and was programmed with a special fuses instead of resistors. Reprogramming meant popping all the fuses then installing a specal programming key which was nothing more than a series of jumpers. I've seen some vehicles where dash programming clip is set for "divide by" ratio of 1 and white box DRAC is installed.

  12. #42
    EFI GearHead ! EagleMark's Avatar
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    Well they are both white boxs and they both have the same plug. But inside DRAC is one set of jumpers, inside VSSB is 2 sets of jumpers. If you plug a DRAC into a VSSB system it melts the new DIP switch. I haven't done much testing after that...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  13. #43
    Super Moderator Six_Shooter's Avatar
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    I think you had other issues, since I haven't heard of anyone else having that issue.
    The man who says something is impossible, is usually interrupted by the man doing it.

  14. #44
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    If you plug a DRAC into a VSSB system it melts the new DIP switch. I haven't done much testing after that...
    No?? Can't imagine why not.


    I've never had problems swapping them around before. Maybe a blob of solder in the wrong place?

  15. #45
    Fuel Injected! CDeeZ's Avatar
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    Quote Originally Posted by dave w View Post
    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
    Wow, and here I thought all this time I have a 4K system in my '90 C-1500. BTW, PPM means pulses per mile correct?



    Quote Originally Posted by 1project2many View Post
    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?
    Does this mean that my C1500 that was originally a 7747 system is 2K PPM, the reason I ask is because on my application it never was a cable driven speedo. I need to boot into the windows side of my HDD when I get back to have another look at all that info as far as the comparo, wondering if maybe I should have that flag checked since I'm manual trans.


    Quote Originally Posted by EagleMark View Post
    FYI DRAC on 1227747 and VSSB on 16197427 and they do not interchange.
    Well the 7 jumper and 14 jumper versions are interchangeable, but on my 7747 the original gauges had the DRAC built into the cluster itself, not a stand alone unit so that is obviously not interchangeable with anything, not easily anyways. The white boxes all interchange though. I think the VSSB/DRAC is basically a nomenclature difference, nothing more. Technically the DRAC is the 7 jumper variant and it was produced from '90-'91 as a stand alone white box unit. Earlier applications using "DRACs" may have incorporated the DRAC into the cluster as my original "moonie" gauges did in my truck. The 14 jumper version is the VSSB and it was produced from '92-'95

    Quote Originally Posted by 1project2many View Post
    VSSB is a type of DRAC. Original reprogramming docs didn't even say "VSSB". All my data shows the "white box" versions are plug compatible but if you have something different I've got an open mind. Earlier trucks had DRAC built into the back of the dash and was programmed with a special fuses instead of resistors. Reprogramming meant popping all the fuses then installing a specal programming key which was nothing more than a series of jumpers. I've seen some vehicles where dash programming clip is set for "divide by" ratio of 1 and white box DRAC is installed.
    I like how descriptive "white box" is Yes I went through that very thing, my truck had what are referred to as the "moonies" gauges and the DRAC is built into the cluster itself... I just desoldered those "fuses" and recalibrated the DRAC for my 4.88 gears by using some high tech jumpers fashioned out of a butchered paperclip. I recently swapped to the "needles" gauges from like a 94/95 C1500 and those did use the stand alone DRAC/VSSB/white box lol, whatever ya wanna call it. While we are on the topic of this I wanted to mention that during my research for how to wire the DRAC, and new gauges and everything, I stumbled across all kinds of conflicting and/or vague information. What I could gather is that the DRACs/VSSBs are basically all pretty similar, they all perform the same function of converting the incoming VSS signal from AC to calibrated DC signal. Some DRACs have slightly different wire locations: for example, occasionally the cruise signal wire from the DRAC is off on a 2nd plug by itself instead of pinned in with the rest of the wires in the main plug. Some have TWO outputs for VSS to the PCM (VSS and TRANS OUTPUT SPEED) and some others I've seen only have one output to PCM/ECM for VSS.


    Quote Originally Posted by EagleMark View Post
    Well they are both white boxs and they both have the same plug. But inside DRAC is one set of jumpers, inside VSSB is 2 sets of jumpers. If you plug a DRAC into a VSSB system it melts the new DIP switch. I haven't done much testing after that...
    Some of them have two plugs. I have used both DRAC and VSSB in my 90 C1500 without issue. Both with DIP switches.

    Quote Originally Posted by Six_Shooter View Post
    I think you had other issues, since I haven't heard of anyone else having that issue.
    Yeah I haven't heard of anyone either.

    Quote Originally Posted by 1project2many View Post
    No?? Can't imagine why not.


    I've never had problems swapping them around before. Maybe a blob of solder in the wrong place?

    Very possible. Possibly the unit itself just crapped out?






    I use VSSB and DRAC interchangeably, the function is basically the same between them. The one problem I can see with the DIP switch install is that with the white case closed, it seems awful close to the rockers on the DIP switch. I don't know if the particular DIPs they had at my local radioshack were bigger than normal or what, but I think I'm going to take one of my extra DRACs and just set it up with jumpers, its not like it's that hard to move the jumpers around if you have too. And if you don't change tires and gears every weekend I don't know if there is really much point to a DIP after having gone to the trouble to install a few DIPs myself.


    Alot of the DRACs I've seen have a DK BLUE wire that is used for VSS output. These DRACs also typically have a 2nd brown wire (main brown wire is +12v for DRAC). Here is where it gets interesting: I opted to use the 7 jumper version the "DRAC" that I had laying around. This DRAC didn't have the DK BLUE wire at all, only the 2nd brown wire. I took the connector off and pulled the plastic comb off and ADDED the DK BLUE wire to a DRAC that didn't originally have it. Both (DK BLUE and the 2nd BROWN) appear to be VSS output signal for PCM: VSS and Trans Output Speed... Initially after swapping to the 7427 I kept getting "LOW TRANS OUTPUT SPEED" error. After connecting the BK BLUE and BROWN wire from the DRAC to the PCM at the respective pins, the code never came back.
    Last edited by CDeeZ; 08-14-2012 at 11:58 AM.

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