The Stovebolt Site Forums The Shop Area Engine Shop 235 carb to TBI swap

I've been running a TBI setup on my 54 GMC with a 302 for about 5 years now. I took a complete 4.3 system from a 90 Astro Van and adapted it.I used a 4BBL manifold from Patrick's and made an adapter for the TB using a piece of 1/2" steel plate. I took the wiring harness apart and used only the wiring needed for the computer, TBI,ignition etc. The hardest part was modifying the 4.3 distrobutor to fit the 302. I already had an old style HEI, but needed the electronics for the TBI system. The old style HEIs are easy to modify to fit a 235, 261, or GMC 6. I know within reason that if you used one of them and used the 7 prong module from a 81-86 GM car with the computer controlled carb you could make it work if you knew how to hook up the wiring for the HEI to work with the TBI. I just haven't found that information. This would be a much easier way than modifying a V6 distributor.
There is a frame mounted fuel pump that will work with the TBI. I will have to find that information on brand and part number. It is listed as a replacement TBI pump.
I mounted the knock sensor in the water drain hole on the side of the block just like it was on the 4.3. I drilled and tapped an extra hole in the thermostat housing below the thermostat. All the sensors, wiring, plug-ins, distributor, are all original factory off the astro van. The only after market items I used were the fuel pump and an electronic speed sensor I ordered somewhere.
The only problem was that the 4.3 TB injectors were too small. I replaced the TB with one from a 350 and it has worder much better, however I still get a lean backfire occasionally. Still needs more apparently. On the whole, I am very satisfied with the system. The 4bbl manifold, the fenton dual manifolds,the fuel pump,the speed sensor, and various steel fuel lines etc. was the only money I spent. The whole astro van cost me nothing. I would have put the manifolds on sooner or later anyway so I cant really count their cost. All it takes is a lot of time, patience, and a good wiring diagram. Hope this helps. Joe Dial
P.S. I didn't notice a real difference in power or mileage between the 2BBL carb and the TBI, but the easy starting, the smoothness, and most of all, the cool factor is what counts.