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

  1. #46
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    If you look around the web, or on this site, you might find a PDF called drac2 with calibration info and pictures and even a pinout. There are scanned documents with fingerprint smudges that show jumper settings for the various "divide by" ratios and images of the two DRAC circuit types. Had I known I'd be uploading those papers to the web in '97, I wouldn't have smudged them back in '93. In '98 or '99 a fellow with some technical writing experience took the original drac.pdf, basically a collection of technician's notes, and re-wrote it as a more presentable paper (drac2). That document also introduced the DIP switch. The included pinout was put together later, maybe in late 99 or 2000 and has a disclaimer as to accuracy. When I researched the pinout I'd often find that a wire or signal had different names in different vehicles but when I'd dig into the service manual the signal itself was consistent. But without a statistically significant sample I wasn't willing to skip the disclaimer. I haven't spoken with too many people who have actually checked these signals. I had two units to test on a bench and both produced signals which matched the pinout. When someone complains to me that they have a unit which doesn't match the pinout it's usually because their service manual calls the signal by another name. It would be awesome if someone either found OE documentation or had enough time and energy to do some component testing so the pinout could be confirmed or removed.

    "White box" is a simple identifier but with some dealership background and some years working on these, I know there are speedometer buffers, ratio adapters, signal buffers, digital converters, and plenty of other monikers that have been applied in service literature. Experience has shown that the green box is the green box, and the yellow box is the yellow box, and the orange box is the orange box, and the blue box is the blue box, no matter what make and model it originally came in. Skip all the service manual nomenclature, just go to the junkyard and get the right color box and you're done.

    Speedometer cables were standardized at 1000 revolutions per mile. Original speed sensors were two shutter wheels which passed through an IR LED and photo detector with each cable revolution. Much of the programming historically descended from code designed to work with these sensors and you'll find many GM speed signals to be an even multiple of 2000 pulses per mile.

    I have a DRAC with a DIP used for confirming correct jumper settings before modifying a customer's part. It's always nice to know you'll get it right before the soldering gun is applied.

    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.
    Yes, and that's part of the question I asked. There is no way to generate a correct "trans output speed" signal with only a 4k ppm generator. So that signal will not be present in an older manual trans swap, even though the 94-95 S/T/C/K applications with 7427 family pcm and manual trans appear to have used it along with a "vehicle speed signal." Can you think of any specific applications which did not have the "trans output speed" signal but may have used the later 7427 family pcm?
    Last edited by 1project2many; 08-14-2012 at 02:15 PM.

  2. #47
    Fuel Injected! CDeeZ's Avatar
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    Quote Originally Posted by 1project2many View Post
    Can you think of any specific applications which did not have the "trans output speed" signal but may have used the later 7427 family pcm?
    I can't think of any off the top of my head, but there was bound to be some. I know that the DRAC I ended up using APPEARED to only support VSS, but when I added another wire for TRANS OUTPUT SPEED, it worked just great, so it appears that the capability for the two outputs is always there on the DRACs, whether it is used or not...

  3. #48
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    Bringing this thread back up with a question.

    in the pin out chart on page 1 it lists.................................
    C16------E13--------Orange-----------Battery (Inputed in place of Brake Switch for TCC to function)
    Why not brake switch?
    I had planned to swap in the cruise as well while I am at it. Will this have any negative effects for the cruise?
    Kinda thinking this would prevent the PCM from cutting the cruise when I hit the brakes.

    Jim
    1978 Cherokee chief
    Current status = BACK under construction
    modified body w/TJ flares
    AMC 360, junkyard 7427 TBI w/ 4L80e
    NWF doubler w/
    upside down 203
    SOA D60/14B-FF
    custom shackle flip w/F150 springs
    H1 wheels + (for now) tires


  4. #49
    Super Moderator Six_Shooter's Avatar
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    Cruise control is a separate system from the EFI.
    The man who says something is impossible, is usually interrupted by the man doing it.

  5. #50
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    Just in case anyone does this swap and has knock sensor issues

    I converted my 89 chevy astro over to the 16197427 (vehicle was converted to a 350 TBI a few years a go). I was having problems with the knock sensor wiring, originally I connected brown and blue together as desribed in this how to. This does not work on an 89 astro. On this vehicle brown is ground and black is the signal to the ECM (now PCM). This is probably an astro specific thing but there may be other GM TBI vehicles with this discrepency so I suggest going by the pinout of the ESC module which is as follows - pin A is empty, pin B goes to +12 volt, pin C is signal to ECM, pin D is ground and pin E to knock sensor. So connect the wires at pin C and E together. Oh and thanks goes to those who pioneered this conversion and those who have worked to perfect it!

  6. #51
    Fuel Injected! JeepsAndGuns's Avatar
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    Just remember the 89 knock sensor is not gonna be the correct one for a 7427, it will need changed.
    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.

  7. #52
    Super Moderator dave w's Avatar
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    I think the knock sensor circuit re-wiring is confusing for a few reasons.

    The original re-wiring information from Thridgen.org was for a passenger vehicle. The information on Thridgen.org comments pickups are similar.
    (3*)= A.) Wire like 1995 P30 Step Van, ESC Module output to B7
    (3*)= B.) Wire like 1995 C10 Truck, Bypass ESC (Blue to Brown) and use Late TBI/TPI 305/350 Knock sensor

    The first time I did this conversion was on a 1987 1 ton 2WD dually pickup with a 454, which is at the start of this tread. Not everyone has access to the wiring diagrams for a 1995 P30 Step Van or a 1995 C10 Truck, so this creates confusion on what to do. The GM Pickup used different wire colors for the ESC module (mounted near the TBI) than the passenger vehicle, which creates confusion. Different years of GM pickup production have different wire colors for the ESC module which creates confusion.

    If doing this conversion without proper wiring diagrams, I suggest the following procedure with multimeter.

    Unplug the ESC module.
    With the multimeter set to volts DC turn the ignition switch on, connect the negative lead of the multimeter to the battery negative connection and probe all four pins on the ESC module connector. Only one pin of the four pins will show a near battery voltage, which identifies which of the 4 wires is the ignition power wire.

    Turn the ignition switch off, and disconnect the negative cable from the battery.
    With the multimeter set to Ohms scale 200K, connect the negative lead of the multimeter to negative battery cable bolt on the engine block and probe the remaining three pins of the ESC module connector. One of the remaining three pins will measure nearly ZERO ohms, which then identifies the ground wire to the ESC Module. One of the remaining three pins will measure nearly 100K Ohms, which then identifies the wire going to the knock sensor.

    By process of elimination the 4th pin in the ESC module is the wire that goes to the ECM. The ESC connector wire that goes to the ECM and the ESC connector wire that goes to the knock sensor are then solder spliced together. The ESC ignition power and ground wires can be left inside the ESC Module connector.

    I typically use then use the old ESC module ignition power wire and the old ESC ground wire for a heated O2 sensor upgrade.

    The last source of confusion is which knock sensor to use. I typically use an aftermarket knock sensor from Standard Ignition part number KS6. I've looked at some of the online aftermarket parts supplier websites; many of the 1993 ~ 1995 GM pickup make / model / year parts catalogs do not show a 4K ohm knock sensor for an automatic transmission only a 100K ohm manual transmission. The Standard Ignition knock sensor part number KS6 is a 4K ohm knock sensor that I have successfully used in the multiple conversion I've done.

    dave w
    Last edited by dave w; 01-11-2013 at 11:13 AM.

  8. #53
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    Yes, the multimeter method is the surefire way to figure out the knock sensor wiring. It is also how I ended up figuring it out. I believe that the pin designations on the modules are the same on passenger cars vs. trucks but the wiring colors are different. I could be wrong though, I don't have both to confirm this.

    I also used the Standard Motor products KS6 knock sensor. It is working great.

    I would have to agree with the people who state this conversion won't make your vehicle run better if you had the original ECM tuned right to start with, but the datalogging is so much better! There is one quirk my van had with the 7747 that has went away now, that I could never get tuned out on the 7747. On cold start at an ambient temp of around 40-50*F I would have to push the accelerator a little bit or it would just flood out with the 7747. If temperatures were colder or warmer than that range it would fire right up with just a turn of the key. Since the change to the 97427 that issue has went away. This could just be an issue with my setup, this engine is far from a stock 350 with more cam than most would consider EFI friendly, and I am sure it could have been tuned out on the 7747 but I couldn't figure it out and the conversion to the 97427 eliminated the need to figure it out. In any case there is definitely something superior about the cold start up routines in the 97427 and it is great having that problem gone after 4 years of dealing with that on daily driving.

  9. #54
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    Quote Originally Posted by d21turbo View Post
    I would have to agree with the people who state this conversion won't make your vehicle run better if you had the original ECM tuned right to start with, but the datalogging is so much better! There is one quirk my van had with the 7747 that has went away now, that I could never get tuned out on the 7747. On cold start at an ambient temp of around 40-50*F I would have to push the accelerator a little bit or it would just flood out with the 7747. If temperatures were colder or warmer than that range it would fire right up with just a turn of the key. Since the change to the 97427 that issue has went away. This could just be an issue with my setup, this engine is far from a stock 350 with more cam than most would consider EFI friendly, and I am sure it could have been tuned out on the 7747 but I couldn't figure it out and the conversion to the 97427 eliminated the need to figure it out. In any case there is definitely something superior about the cold start up routines in the 97427 and it is great having that problem gone after 4 years of dealing with that on daily driving.
    GM loves to switch around the wire colors. I recently swapped my L31 black box to a 0411 in my 97 Express using a guide for a 97 C1500. Found several discrepencies with that swap as well.

    The 427 swap was very new when I wrote that guide on TGO, very few had done it and the info was scattered across numerous posts and sites. I swapped my 83 G20 first using a 92 G20 harness, followed by th 87 GMC Jimmy 2.8 and a RS Camaro.

    Having done 3 different swap, all on well tuned setups, I have to say the newer 7427 has noticeably better driveability than an earler TBI ECM. They ran smoother, were more responsive, responded to changing conditions better and just all around performed better. The real improvement was E-transmissions however.

    I will also add I have a 95 G-series calibration I found with the a/c high pressure switch active and I believe the 95 trucks used them too.
    Last edited by Fast355; 02-17-2013 at 02:13 AM.

  10. #55
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    Chris how did you find this website?!?! That's it, Fast has made his arrival, time to shut the forum down! LOL JK man, glad to have you on here with your EFI-veteran status!



    I agree on trying to eliminate the confusion on the knock sensor wiring when upgrading from the 747 ECM to the 7427 PCM, I went through the same thing myself. Blue to brown gives you two grounds on some GM vehicles (which obviously won't work b/c that's only half of the circuit). The multimeter is the only surefire way. It also doesn't help that the wire colors underhood are further obscured by fading/grime accumulation.


    Also, I'm not as learned as some of the guys on here, but I have to agree, with what little I know, that the 7427 does indeed have better cold start routines, and also is just better all around in my opinion. Perhaps part of this is the additional resolution on things like fuel tables?
    Last edited by CDeeZ; 02-25-2013 at 08:44 PM.

  11. #56
    Super Moderator dave w's Avatar
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    TH400 Kick Down Relay control TH 400 auto to 16197427 PCM

    I think this is a good tread to post a budget update about converting a vehicle with the 1227747 / TH400 combination to a 16197427 PCM which does not have a TH400 Kick Down control.

    On vehicles with a 1227747 the TH400 Kick Down Relay is controlled by ECM pin A7 (tan wire with a black stripe), which sends a ground to the Kick Down Relay. The simple budget fix is to install a TH400 Kick Down Switch on the Accelerator Pedal, just like the older non-computer controlled GM Pickups used. The HUGE difference is ECM pin A7 will be switched to ground (black wire with a white stripe) through the Kick Down Switch to make the TH400 Kick Down Relay work. One side of the Accelerator Pedal Mounted Kick Down Switch will be connected to ground and the other terminal of the Accelerator Pedal Mounted Kick Down Switch will be connected to pin A7.

    For a long term trouble free service, solder splicing the wiring is HIGHLY RECOMMENDED!

    The pictures below are from a 1987 C3500 454 / TH400 that has been updated to a 16197427 PCM that is using an Accelerator Pedal Mounted TH400 Kick Down Switch. The older Accelerator Mounted TH400 Kick Down Switch is a direct bolt in, no modifications required.

    dave w
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    Last edited by dave w; 05-05-2013 at 09:15 AM.

  12. #57
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    Quote Originally Posted by dave w View Post
    I think this is a good tread to post a budget update about converting a vehicle with the 1227747 / TH400 combination to a 16197427 PCM which does not have a TH400 Kick Down control.

    On vehicles with a 1227747 the TH400 Kick Down Relay is controlled by ECM pin A7 (tan wire with a black stripe), which sends a ground to the Kick Down Relay. The simple budget fix is to install a TH400 Kick Down Switch on the Accelerator Pedal, just like the older non-computer controlled GM Pickups used. The HUGE difference is ECM pin A7 will be switched to ground (black wire with a white stripe) through the Kick Down Switch to make the TH400 Kick Down Relay work. One side of the Accelerator Pedal Mounted Kick Down Switch will be connected to ground and the other terminal of the Accelerator Pedal Mounted Kick Down Switch will be connected to pin A7.

    For a long term trouble free service, solder splicing the wiring is HIGHLY RECOMMENDED!

    The pictures below are from a 1987 C3500 454 / TH400 that has been updated to a 16197427 PCM that is using an Accelerator Pedal Mounted TH400 Kick Down Switch. The older Accelerator Mounted TH400 Kick Down Switch is a direct bolt in, no modifications required.

    dave w
    Dave,

    Interesting idea however I am thinking a small patch could be added to control the downshifts similarly to the shift light logic. No extra hardware created.

  13. #58
    Super Moderator dave w's Avatar
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    Quote Originally Posted by Fast355 View Post
    Dave,

    Interesting idea however I am thinking a small patch could be added to control the downshifts similarly to the shift light logic. No extra hardware created.
    I agree, a small patch would be a good option.

    dave w

  14. #59
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    I am planning on switching from the 7747 to the 7427. Need to the get the PCM itself tho, and since I have a V8, do I need a 7427 from a V8, or will the V6 version work too?
    '90 Suburban w/ pretty much stock 350 TBI, 7427 ECM Conversion

  15. #60
    Super Moderator dave w's Avatar
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    Quote Originally Posted by TheApocalyptican View Post
    I am planning on switching from the 7747 to the 7427. Need to the get the PCM itself tho, and since I have a V8, do I need a 7427 from a V8, or will the V6 version work too?
    I've never tried using a V6 Memcal for a V8 engine. I've done several '7427 conversions, all V8 engines and all had V8 Memcals.

    dave w

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