Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - TBI to carb conversion wiring?
View Single Post
  #2 (permalink)  
Old 06-02-2012, 08:22 PM
Pre-Tuner Pre-Tuner is offline
406cu.in. of tire smokin' fun
 

Last journal entry: 406 Build Thread
Last photo:
Join Date: Jun 2008
Location: Tacoma, WA
Posts: 232
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
Right now the ECM turns on the fuel pump. You will need to wire it so that it comes on with the ignition. The ECM sends a negative signal to the relay now, so you need to cut the wire and ground it. This will make the relay stay on all of the time, so you need to cut the hot side and wire that side to the ignition. Actually, the signal from the ECM goes through the oil pressure sending unit to the relay. This is incase you lose oil pressure it would shut off the fuel pump to save the engine. I doubt it matters much with a carb because there is enough fuel in the float bowls that the engine will already be toast by the time you run out. Obviously with fuel injection once the fuel pressure stops the engine will immediately die.

You will need a new distributor. The one you have is computer controlled, and obviously you won't be using the computer anymore. Just a standard HEI will work just fine. I went with a Mallory because it is billet and far cheaper than a billet MSD. Take a look around on the internet. The MSD HEI distributors are identical to several other brands anyway except they say MSD. I didn't quite believe it until I saw with my own eyes. I'm sure their boxes are nice, but don't waste your money for the MSD name on an HEI distributor.

When I converted mine, I disassembled the whole ECM harness and traced all of the sensor and actuator wires from their connectors to the ECM. This told me what I didn't need anymore and I knew it was safe to cut them. There are two connectors at the ECM. Almost every wire you will get rid of but there are a few than you will keep or at least need to know what it goes to, like the fuel pump relay. There wasn't many, but I think I also had to rewire something for the A/C.

You will need to run an igntion wire for the new distributor, and your carb choke. DO NOT use the same wire for both. You will lose the temp sensor on the passenger side because that is the ECM temp sensor. The one for your gauge is on the drivers side and you won't have to do anything at all to keep it working. I belive the only other wires I kept for the engine was for the alternator and the A/C clutch.

You will also need to regulate your fuel pressure. The pump you have is regulated through the TBI and without the TBI it is capable of pressures well beyond what your carb will need. I already had an Aeromotive bypass regulator so that is what I used. I think there are cheaper methods out there that will work like a dead head regulator but you might want to do some research just to be sure. Cut the fuel lines just after the fuel filter and loose the connecting pipes that used to go to the TBI. They get in the way of the distributor. Run the lines to the inner fender and then a line over the engine to the carb.

I think I have some pics of what mine looks like on this forum somewhere. Just do a search. My project was (and still is) a '91 C1500 truck.
Reply With Quote