1979 GMC Dually TBI swap

**Randy 79** · 06-04-2013

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.

**Randy 79** · 06-04-2013

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

**EagleMark** · 06-04-2013

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!

**Randy 79** · 06-04-2013

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.

**Randy 79** · 06-05-2013

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.