Here are some pics of my winter project. I am all thumbs with a carburetor. I do tinker with old IH trucks and such and have always converted them to throttle body fuel injection with Chevy parts from the late 80's-early 90's. My wife's 78 Spider ran ok, but wasn't perfect. The guy who tuned my other projects mentioned I should try to put TBI on the Spider.
So I set out to find a single barrel throttle body that was close to the 1.8L. My best option turned out to be a throttle body from an 89 Chevy S-10 with a 2.5L four banger. I grabbed the throttle body, engine wiring harness, PCM, and all sensors from the motor. I'm using an O2 sensor, coolant temp sensor, MAP sensor, the GM coil and ignition module. I ended up not using the S-10 PCM due to it not being a widely supported PCM for tuning. I am using a V-8 ecm from a Chevy 1500 pickup. The conversion wasn't as scary as you might think. There is plenty of info on converting carb'ed vehicles over, with wiring diagrams and such.
The site that I use(almost daily) is BinderPlanet.com. There is an "Injection Forum" there moderated by a FI guru named Bill Hamilton(Hamilton Fuel Injection).
For ignition, I modified a Fiat electronic distributor. I disabled the mechanical and vacuum advance, so the ECM controls all the timing. No more points. That's what makes this system so neat is that the computer controls timing too, not just fuel.
I was able to get the Spider to run with the V8 programming, but the since there was only one injector to fire, it ran really lean. It would idle all day long, but it couldn't pull itself. Bill Hamilton has done similar 4cyl conversions using V8 ECM's and had a "base" tune for me to try. After some testing and driving, we arrived at a very nice tune for the Fiat. This car now starts, accelerates, and idles like a modern vehicle. Obviously, I'm not a Fiat purist, nor am I one to totally hack something up. I was just looking for something different. As a side benefit, this system is super reliable and parts are cheap and readily available.
The other "custom" part aside from the modded distributor is the adapter plate. I used a 1" thick piece of aluminum plate. With some careful measuring and a drill press, I was able to build a decent plate. Believe it or not, there was room for the air cleaner under the hood even with a 1" spacer. The only tricky part of the adapter plate was creating a vacuum port in it for the Idle Air Control Valve. This valve basically opens and closes to create a vacuum leak to raise or lower idle.
So far, my wife has put 100 miles or so on this system. The ecm is capable of a +/-10% "learning" curve, it can adjust that much. She really likes the smooth acceleration, easy starts, and the possible economy gains(we'll see on that one
)What do you all think?
Lynn(Ian)