Thanks for highlighting the pitfalls. Didn't think about the tank, pump, lines or intake design changes.
It's a 76 Chevy C30 with a 1970 400 small block usually hauling 3 tons. Figuring per ton mileage isn't bad. The odometer's not working so mileage is a guess anyway.
If I go TBI, I'll need to buy a mid 80's roached donor truck.:rolleyes:

I don't think they ever fuel injected the C30 on that body. I know when I was the vehicle officer at the rescue squad we had an old 1989 Chevrolet K30 ambulance with a 454 in it for driving in the winter, because so few of our roads were actually plowed. That truck had a carb in it, no fuel injection. Because of that I don't think they switched to FI on the 1 tons until they switched the 1 ton to the new body (90 or 91 I think) I'm not sure how a FI system designed for a 350 and a 1/2 ton truck will do with a 400 and a 1 ton chassis/load. I'd do more research on it first, and maybe do one of the Holley FI retrofit systems designed to replace carbs, at least you will be able to tweak the settings with a laptop so it will run right if necessary.

-Jay

I drive a 1988 model CBS (73-87 pickup body style) 3/4 ton Suburban with a 454 TBI. The model 700 TBI unit in that is the same body as the 350 (5.7) and 305 (5.0) V8's, and even the 4.3 and 2.8 V6's. The 2.8 has the smallest bore, 4.3/5.0/5.7 have the medium size, and the 454 is the largest. Injectors match bore size for each. So a 4.3 TBI unit is the same as a 5.7 TBI unit. That means Astros, S-10 Blazers, pickups, vans, and Suburbans all have the same unit and are interchangeable. TPS sensors changed mid-year in 1989 so get the harness from the truck you pull it from to make sure it's right. All this info comes from here:

https://s-series.org/component/option...,26/task,item/

The directions to change a small TBI for a large one will be similar to changing out carb for TBI. Of course you'll want the throttle cable, all the sensors and vacuum hoses, and the computer and wiring harness, unless you go aftermarket (MegaSquirt, others).

As far as C30 CBS trucks getting TBI, I know the 1987 models were still carbureted. Look at the 8th digit of the VIN code. R means it's a 350 TBI. K, L, or M means a 350 4bbl Q-jet. F and G are a 305 with a carb. H is a 305 no matter what, but can be carb or TBI. Z is the 4.3L V6. They made CBS trucks through 1989 for sure. CBS Suburbans through 1991 but Suburbans were TBI from 1987 on (for the most part).

IIRC Suburban fuel tanks fit real nice where the spare is on a 73-87 pickup. 40 more gallons of range. (OR 26 or 34 depending on the tank you grab, most were 40 though)

TMI yet?

believe it or not, occupant, the 4.3L and 5.7L have the same bore and stroke.