Throttle Body Injection (TBI) for a pre-TBI 350

Why: After running my '65 Chevy pickup for a couple of years with the stock '83 drive train (350/700R4), I got tired of the constant battle I was having with the Quadra Jet. It never seemed to run as great as I thought it should and it was starting to do strange things (like flooding whenever it felt like it). I couldn't take it anymore and I couldn't find anybody who seemed to be knowledgeable enough to make it work. A new Q-Jet was in the $400 range so I figured why not try a TBI system. They are easy to find, relatively inexpensive and as bullet-proof as they get. So my search started for a GM TBI unit.

How: The first step was to do a little research. The internet proved to be a great source of information. It turned out that people are putting GM TBI units everything from Jeeps to Land Cruisers. I jumped on eBay and starting bidding. I ended up with a complete system from a '91 305 Camaro for about $140. It included the TBI unit, the intake manifold, the ECM (computer), the distributor, the wiring harness and most of the sensors. I downloaded several pinout charts and wiring diagrams and began studying every detail.

  I started with the harness and began by labeling every single connector, sensor and wire. I determined there were several things in the harness that I didn't need, such as the windshield wiper controls, power steering tuff, etc. Since I don't have to be concerned with emissions I decided to eliminate the EGR system. I removed all wiring that would not be used and ended with a harness that just runs the fuel system. Next I installed all the hardware on the '83 small block 350; the intake manifold, the distributor and the TBI unit. Once in place, I laid the wiring harness in and figured out where I wanted to mount the ESC unit, the MAP sensor and the fuel pump relay, as well as where to place the hole in the fire wall for the harness to get inside the cab where the ECM was to be mounted. Then I had to shorten several legs of the harness so that I wouldn't have big bundles of excess wiring laying all over the inside of the engine compartment. With everything mount and the wiring ready and in place, it was time to hook everything up and turn the key.

  The moment of truth was very disappointing. When I cranked the engine it just didn't want to play. If I dribbled a little gas into the throttle body, it would fire right up and run great for about three seconds! Back to the drawing board.... I got out the digital multimeter and started checking all the pins in the ECM. I soon discovered that I was totally missing the ground to all the sensors (IAC, MAP ETS and TPS). Once that was fixed I turn the key and the engine fired up great but as soon as the key went back the the "run" position the engine died instantly. I got out the meter again and checked everything twice. I found a couple of minor mistakes but no show stoppers. I got into a couple of different forums and asked some questions and got some great advise but nothing fixed the problem. Finally, a friend of mine loaned me an ECM for a try. I was sure it wouldn't make any difference. I mean, I did buy everything on eBay!!! I plugged the "new" ECM in and it ran like a brand new engine!! It turns out that the '91 Camaro ECM supports VATS (vehicle anti-theft system) and since it wasn't seeing the chip in the key it wouldn't dance.

The ECM is mounted underneath the dash on the firewall with a home-made bracket.

The ALDL connector is mounted under the lip of the instrument panel. The "service engine" light is a little plastic suface-mount LED I picked up at Radio Shack for $2. Too small to see in this photo, it's mounted next to the ALDL.

Here you can see where I mounted the ESC (electronic spark control) module. I came with a bracket that also holds the fuel pump relay. If you look closely under the bracket you will see the wiring for the knock sensor, which hasn't been installed yet.

I bought a throttle cable/TV cable bracket from my local Chevy dealer for a '91 Chevy pickup and it put the cable ends in the right place so I didn't have to modify either cable and their orientation to the throttle body was just right. You can see where I went through the firewall with the wiring just above the distributor. With  my factory air, I didn't have many other options. If you are installing a TBI system on a vehicle and are using a TH350 transmission, here's what you do for a kick-down cable.


If you have any questions about this installation, feel free to drop me a line. It's been an interesting project and it's not over.



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