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Thread: 1979 GMC Dually TBI swap

  1. #1
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    1979 GMC Dually TBI swap

    This is kinda my build thread I guess, so I will update it as I go. I'm working on a 79 GMC Dually that I tow a 28ft enclosed trailer with. It was a 454 truck but has a 350 now. Still has the SM465 M/T in it, with 3.73 gears. It does a decent job pulling the trailer but the 350 works quite hard and slows down on hills. More power was needed. So, I picked up a 92 Suburban 4x4 Gen V 454 TBI (at machine shop, being rebuilt). I was going to run it carbed, but since I have to run an electric fuel pump, thought it might be good to use the TBI stuff it came with. Didn't hurt it came with an Edelbrock TBI intake, ported TBI with spacer and AFPR, air cleaner, wiring harness, all sensors, and computer (7060, BANF chip). Since the truck is a manual, it will be fun to get everything to work together. I will need a new chip, may just get someone to make one for me to get it going.

    I have already unwrapped the harness and removed the unnecessary wiring. I do want to keep the 4L80E wiring intact in case I decide down the road to go with overdrive. I still have quite a bit to figure out but I am getting there. I got a 92 wiring manual which has helped quite a bit and wiring diagrams from this site as well. Should be a fun project. I have previously swapped a 94 LT1 into a 67 El Camino with a Painless harness, so not totally green on EFI swaps.

    I have a few questions, but I will have more later I am sure.

    1. As for the speed sensor, can I wire it to the ECM, instead of using the DRAC that I got with the engine (no wiring to connect the DRAC, must have been part of the underdash harness)? If so, would a sensor like #2PRS from JTR work (2-pulse for TBI), or do I need a different one? It needs to work with the sM465 and my speedo cable.

    2. Is there anything on the a/c that needs to go to the ECM, for idle control or anything else? Hard to tell from the 92 diagrams due to the electronic climate control the Suburban had.

    3. I would like to put a hidden switch to the system as an anti-theft device. Is it best to put it on one of the ECM power leads or maybe on a random wire? Something to keep someone from starting the truck and driving off with it and my trailer.

    4. I will be running dual fuel tanks, truck only has one tank now. Is it hard to put the selector valve in with TBI in tank pumps? What is a good pump to use? The adjustable fuel pressure regulator is set to 25 psi per the previous owner, would that affect pump selection?

    5. Cam selection. The current cam in it is worn so I need to replace it. The previous owner (a friend) is pretty good with EFI stuff and had an unusual cam in it, at least to me. It had a Comp Cams 11-400-4 blower/turbo cam, specs here: http://www.compcams.com/Company/CC/c...?csid=426&sb=0 It was run NA for 150K miles, so it did work. He said it had more mid-range torque than the TBI cams, and stopped pulling at 4800 rpms. Any thoughts on this? Of course we joked it would be good for adding boost to the 454, but I'm not sure if the injectors would be able to handle the extra fuel requirement. It will be NA for now, adding forced induction would be way farther down the road if ever.
    2003 Chevy Suburban K2500 8.1L tow rig
    2018 Chevy Cruze LT Hatchback 1.4L T
    1975 MGB Roadster L36 3800 S2 conversion
    1979 GMC Dually, 92 Gen V TBI conversion-Sold

  2. #2
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    Oh, here is a picture of the truck and the engine when I first got it.

    2003 Chevy Suburban K2500 8.1L tow rig
    2018 Chevy Cruze LT Hatchback 1.4L T
    1975 MGB Roadster L36 3800 S2 conversion
    1979 GMC Dually, 92 Gen V TBI conversion-Sold

  3. #3
    RIP EagleMark's Avatar
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    Nice truck!

    Those cam specs look horrible without boost.

    There are a couple bis to set/unset for VSS Drac or Mag so probably be able to run VSS to PCM without DRAC/VSSB, there's no need for signal to speedo on your truck or accurate speed for the E trans so I don't think that is a big issue.

    Plumbing, switches and valves for duel tanks is an absolute nightmare and expensive, unless you find a dual tank truck at junk yard for all the parts!

    Hidden kill switch is easy and can be done many differant ways.

    There is a wire for A/C on and very easy to wire in.

    But I don't think that PCM ever had a manual trans? Pretty sure not. You may be better off using the harness and wiring in another ECM? There's so much differant in man to auto bin files.

    Hope that get's you started!

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

  4. #4
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    Thanks for the info Mark. I wasn't sure if the 7060 ECM could work with a manual, that may present a problem. So if I need to change the computer, which one should I get? Does it needs to be for a 92-93 TBI with manual. Since my harness doesn't have a connection for an external ESC, does that limit my computer choices? I believe I will have to change the pinouts for the different ECM as well.

    This was one concern I had with using this TBI setup, that I would end up having to change parts out (cost more $$$$). I hoped to use what I had to keep costs down. Otherwise my backup plan is to go old school, as I have a carb and HEI distributor for it, I just need to get an intake manifold for it. I'll see what I am looking at cost wise with the TBI before the backup plan comes into play.
    2003 Chevy Suburban K2500 8.1L tow rig
    2018 Chevy Cruze LT Hatchback 1.4L T
    1975 MGB Roadster L36 3800 S2 conversion
    1979 GMC Dually, 92 Gen V TBI conversion-Sold

  5. #5
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    Well, after some searching, it looks like the 1228747 computer is the one to use with a manual trans. This should simplify the installation, price is pretty cheap for it, both at parts store and ebay (no core charges on ebay for the most part).

    I have the wiring diagrams from this site so now to figure out what pinout changes I will have to make. Good thing I have time to figure this out, the 350 is getting the job done for now. More updates later.
    2003 Chevy Suburban K2500 8.1L tow rig
    2018 Chevy Cruze LT Hatchback 1.4L T
    1975 MGB Roadster L36 3800 S2 conversion
    1979 GMC Dually, 92 Gen V TBI conversion-Sold

  6. #6
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    your wiring hornass don't have a spark control module plug ?

  7. #7
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    No it doesn't, ESC is in the ECM on the 7060. The 8747 doesn't have KS or ESC, so at least I shouldn't have any issues with that, hopefully (knocks on fake wood).
    2003 Chevy Suburban K2500 8.1L tow rig
    2018 Chevy Cruze LT Hatchback 1.4L T
    1975 MGB Roadster L36 3800 S2 conversion
    1979 GMC Dually, 92 Gen V TBI conversion-Sold

  8. #8
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    I would personally repin your harness and use the '7427 PCM , run it with your manual trans now and have the capability there for an '80E if you choose down the road .

    Also, try if at all possible to run the knock sensor and system , especially if it will see towing / hauling duty , don't know why GM didn't use it on some , kinda weird.....

    I would simply wire in the DRAC now , it is needeed for E trans control (as I have found out) and is much easie4r to add it now and not need it than to need it and not have it.

    That cam , as Mark said , will be a dog without boost . If you are replacing it , I would go roller and not look back . Cant see the timing cover in the pic but you can either check that or the lifter valley , some very late GenV's were drilled and tapped for the roller lifter retainer , this was at the point they were getting ready to release the GenVI , timing cover would have 6 bolts and be either composite or aluminum. Might get lucky ......

    The injectors will support a fair amount of boost (ask me how I know) , but be warned the 3764 intake will be the restriction , might want to think about a good single plane if you force feed it in the future. Bit high on the F/P that he was running if it was N/A but a slight correction and you should be good to go.

    Also , you can loose the 45 degree oil filter adapter if you want to in your picture , you won't need it and it will make header / manifold fittment easier. Engine was out of a 4X4 I assume ?

    Nice truck , wish I would have kept my '79 crew cab Dually , my plan was exactally like yours , TBI BBC / 4L80E , all with a '7427 to control it. Oh , and a blower

    TOM
    Last edited by Nasty-Z; 06-05-2013 at 09:34 PM.
    1994 3500 Dually , 502 (509) , 264HR , Edelbrock MPFI , PFI '7427
    1992 S-10 434 SBC/Tremec - '7427
    1986 Monte Carlo SS
    1984 S-10 , SAS, 496/700R4/205 , D44/14BFF -'7427
    1980 Z-28 496/700R4
    1979 Corvette 496/700R4
    1977 Olds 98 Regency 403/700R4

  9. #9
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    If you can use the 7427 with a m/t, shouldn't you be able to do that with the 7060 as well? Just wondering. KS would be nice to keep but not a necessity for me.

    As for the trans, this truck will stay m/t, pretty much decided against the 4L80E. I want to get a 4-door truck down the road, just not enough room in the standard cab. So I won't need the DRAC on this truck but I do have it just in case.

    As for the cam, PO said it wasn't a dog and matched up well with the 96 Vortec 454 Suburban he replaced it with. The cam is worn so I will be changing it anyways. Block is a 92 and no provisions for roller cam, plain steel timing cover. Just going with flat tappet for now due to costs.

    No boost plans, just having fun. The adapter is already off the block (motor was in a 4x4 Suburban).
    2003 Chevy Suburban K2500 8.1L tow rig
    2018 Chevy Cruze LT Hatchback 1.4L T
    1975 MGB Roadster L36 3800 S2 conversion
    1979 GMC Dually, 92 Gen V TBI conversion-Sold

  10. #10
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    I would pick egale marks brain before I started buying stuff, I worked on a hot rod 454 some one changed from a 350 my scanner kept asking for a esc module there was no wires for that sensor or a knock sensor, I sent him to a hotrod shop I put a 8747 an a 7747 with a good bin file in it, still wanted esc an knock sensor. I don't know if they got it fixed or not, I think it needed a wiring hornass out of a 1990 454- std trans.

  11. #11
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    Sounds like you have it well in hand then.

    Good luck with the project.

    TOM
    1994 3500 Dually , 502 (509) , 264HR , Edelbrock MPFI , PFI '7427
    1992 S-10 434 SBC/Tremec - '7427
    1986 Monte Carlo SS
    1984 S-10 , SAS, 496/700R4/205 , D44/14BFF -'7427
    1980 Z-28 496/700R4
    1979 Corvette 496/700R4
    1977 Olds 98 Regency 403/700R4

  12. #12
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    A lot of BB did not come with knock sensor in 7747 but they can be added and bin straightened out.

    Swapping to 97427 is same as what you have, no manual bins to start. We've done 97427 with a $0E manual bin and found it's easier and better runner with a $0D auto bin. So I'm going to retract what I first said about a possible ECM swap. Why go to a slower ECM, add wiring for ESC and knock?

    That boost cam has backwards split duration steps for boost, can't see it doing anything but hurting performance without boost...

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

  13. #13
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    Tom, I wish I had it well in hand, I have been confusing myself as much as I am figuring stuff out. I appreciate the help and info I am getting here.

    So Mark, are you saying that the 7060 can be used? If I can use it, that's good news.

    I will be going with something different than the turbo cam, just to be on the safe side. Are the Comp TBI cams a good choice or is there better choices? Trying to stick with flat tappet to keep costs down. The PO did convert it to adjustable valvetrain thankfully. As for how the turbo cam worked, all info is what the PO told me, I never got to see it run, engine was out of the vehicle already.
    2003 Chevy Suburban K2500 8.1L tow rig
    2018 Chevy Cruze LT Hatchback 1.4L T
    1975 MGB Roadster L36 3800 S2 conversion
    1979 GMC Dually, 92 Gen V TBI conversion-Sold

  14. #14
    RIP EagleMark's Avatar
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    Quote Originally Posted by Randy 79 View Post
    So Mark, are you saying that the 7060 can be used? If I can use it, that's good news.
    I would. May take some tweaking of things for manual, but way better then the swap option.

    If you have an available manual bin then it saves some time. Most differences in manual to auto calibrations has to do with Decel, DFCO, IAC. Think about it, how do you drive an auto compared to manual? Most of these tweaks had to do with the deceleration/let off throttle between shifts for emmissions, some are drivability.

    But like I said above the guys, myself included ended up with an auto bin in 97427 that was way better then the available manuals... so it can be done. Your PCM is closer to a 97427 then a 7747 or 8747. Actually history wise it was first edition. Had it been in more vehicles it would be just as popular. Very capable. Just can't recall anyone going manual with it. When the 454 came with manual it had the older/slower ECM 7747/8747.

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

  15. #15
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    Well, about time for an update. I haven't had much time to deal with the EFI swap, too many other things happening. Should be getting the rebuild on the 454 wrapped up here soon. Hope to start the swap probably in November. I am getting a Dell laptop with Window Vista. It was my nieces who got a new laptop. Nice present for me. Now I get to learn all about this EFI stuff.

    After doing plenty of research on dual tanks and EFI, I think I am going to have the aux tank feed into the main tank. Seems an easier way than trying to get the selector valve and all the necessary parts together. Unless I happen to luck upon a truck with all the stuff.

    Hopefully I will have more updates here soon. Thanks for all the help.
    2003 Chevy Suburban K2500 8.1L tow rig
    2018 Chevy Cruze LT Hatchback 1.4L T
    1975 MGB Roadster L36 3800 S2 conversion
    1979 GMC Dually, 92 Gen V TBI conversion-Sold

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