4.3 TBI to 5.7 TBI Swap Questions

[erichevy]

I have a low mileage (65,000) 1988 Suburban Silverado that has some major body rust issues. I’d like to pull the 350 tbi/700R4 and all associated parts to swap into my 1987 R10 SWB Truck. The R10 truck is very plain jane, 4.3 w/ manual trans. I think the only option the truck has is A/C. I’d like to use the full gage cluster from the Suburban, the steering column, cruise, delay wipers, pedal assembly, etc. Also planning on swapping the core support/4 headlight set up from the Suburban too, since the truck is only a single headlight on each side. I want to be sure to grab everything I can from the Suburban before it goes to scrap.

So… can I just use the entire wiring harness from the Suburban? Is that required to use the full gage cluster from the Suburban? The truck just has the idiot lights. Maybe I only need the engine harness. I am assuming that would be the easiest thing to do. I realize the Suburban has a lot of interior lighting that would not be needed, but the rest should be the same I would think. I am not sure about the truck’s dual tank system either. I don’t fully understand the dual fuel tank set up on my truck and how this would work if I changed over to the Suburban harness. My truck is actually missing the driver’s side tank and using a single tank already, so sticking with one tank isn’t an issue I guess. It would be nice to have a reserve tank tho. Would a rear mounted tank between the rear frame rails be a better/easier option?

Wiring intimidates me a bit so hopefully I’m not asking too many dumb questions.

Do I need to use the transmission cross member from the suburban? I’m guessing I may need to have my drive shaft modified as well. Would it be a good idea to use the rear axle from the Suburban? Not sure if the truck gear ratio would be different.

Having a running/driving and 100% stock donor vehicle is a bonus at least.

My goal is to have a factory looking set up when I’m done.

Just looking for advice on the swap before I begin. Thanks in advance!

[87 STEPPER]

Every thing you asked about is doable I'd take the entire wiring harness and fuse block from the Burb and install it into the truck. Delete the systems that don't apply to the truck. Just mark every thing as you remove it and then when it's all out lay it out on the floor and start deleting. Then install it in the '87.

BTW The wiring harness in both trucks are split into 3 separate harnesses at the fuse block on the engine side of the fire wall so you don't need to remove the one that go's to the rear for the tail lights. The remaining 2 are the Engine harness you will need to swap them to match the 5.7 And the one that go to the front clip if your gonna do the core support swap.

Yes you will need the Instrument cluster from the burb and the trans x member and you will probably need to have a drive shaft made but that's no biggie!

As far as the dual tanks on the truck I would follow the wiring harness starting from the transfer valve back to where it transitions into the main harness and keep following until you find out where each wire terminates some will go to the switch and others will go to main fuse block de-pin them from there cavity in the fuse block and mark the wires location so you can insert them in same cavity in the Burb's fuse block.

This will be a big endeavor but you probably all ready know that.

BUT!!! It will be worth it when your done.

Good Luck.

[D13]

1. Buy a wiring diagram book, about $30 on evilflay last I checked. 1987 is the one you want, the burb should be about the same.
2. Swap motor / trans, complete with wiring under dash. Use a little silicone on the grommets when installing. You will need to swap the ECM (Computer) too as that will n ot be compatable.
3. Check if the fuel lines to TBI attach at the same plce relative to the firewall. I'm guessing they will.
All the rest should plug in.

Start with your single fuel tank then address that system later. THe oil switch and ECM prime circuit should both feed the tank switch which tuns on the desired tank.

I sent you a private message.

[Greenlee]

I used the wiring harness from an 89’ Suburban when I rebuilt my truck. I’m intimidated by wiring also, but it really wasn’t that hard. Everything is plug and play. Each system, including the dual tanks, have their own separate harness. It’s just tedious work getting all of the wiring out without breaking anything. Once you get it all out, you will have the fuse box and a bunch of separate harnesses for lights, windows etc that all plug into the fuse box. You will need the computer from the Suburban. The computer itself might be the same, but there is a different chip that plugs in for the 4.3 vs. 5.7. I have an old build thread on here somewhere from when I did my truck.