I just recently purchased a 91 RS w/ a 305 TBI. I will be dropping in a carbureted 355 in a couple of months. I've already pulled out the old engine and I have some questions as to what luxuries I can keep. I would like to keep the A/C and cruise control. I'm 99% sure keeping the A/C won't be a problem however I'm not too sure on the cruise control. Since it'll be a carb engine with an HEI I won't need a whole lot of the old wires. Is it possible to keep the C.C. with a carbureted set up or would I be best to just take it out and sell it?

Rusty

 

You can use it. You will need the carb brackets and cables from an LG4 car. You may need an LG4 computer as well (circa 1987) to run everything properly. You need a computer to cycle the A/C properly, to run the cruise properly, and to lock up your torque converter. As far as not needing the old wires, I think you will still need all of the sensors for your accessories to run properly.

 

I've read how to bypass the ECU for the torque converter. Is there a way to bypass the ECU for the A/C? I can live without cruise since this is only a toy. Which accessories will require the ECU and factory sensors? I had planned on running mechanical temp, oil pressure, and volt gauges since I don't trust the factory electric ones.

 

If you don't care about cruise, none of the accessories rely on the ECM. The AC doesn't interface with the ECM on 3rd gens.

 

Most of my schematics show the A/C interfacing with the ECM on 86 and newer models, with my 91 Firebird (not Camaro) wiring schematic showing the TBI 305 running with ECM interference. It shows a light blue wire coming from pin B8 to the A/C compressor controls.

I'm no A/C expert and my schematics show differences with A/C wiring year to year and engine by engine. V6 engines tend to have at least two wires from the A/C system to the ECM and the V8 engines have at least one. Carbureted engines don't seem to interface at all.

 

I'll look into whether the ECU powers the A/C. I can't think off the top of my head why the ECU would need to interface with the A/C but then again ya never know. I mainly want to get rid of all the excess wires in the engine bay so that it looks nice and clean but I also want to keep some items that will make it more attractive down the road if I want to sell it. I should have my short block assembled by this weekend or so I hope.

 

Well I removed all the ECM wires and 75% of the wiring harness (with only a few cuts). I have found two things. One is big rubber/plastic ball in front of the drivers side fender that has a vac line attached to it. What is this for? A reserve tank for the cruise control maybe? Also there is a rubber hose and wiring tape together that ran from the cruise control into the cab and up under the dash. What is this and what can I do with it?


On another note I would like to keep my air bag for now. Has anyone kept their airbag after a swap to a carbureted engine? Is the air bag control by the ECM in any way?

 

The rubber hose is a vacuum line going to the brake switch. Part of the cruise control system.

Can't help you on the airbag question.