I knew GM had installed two forms of fuel injection on the 2.8 V6. First was the TBI (throttle body) unit used on S-10, S-15, Blazer, and Jimmy. The second was MPI used on all 2.8 V6 cars, such as the Camaro, Cavalier, Celebrity, Fiero, and others I'm probably forgetting. This unit would net me the most power (Dad's 1986 Z-24 Cavalier ran strong) but would be the hardest to find, most complicated, and most expensive. Also, for the throttle body on the MPI to face the front of the truck would require a manifold from a Camaro (or possibly Celebrity, but I am not sure) which would be difficult to find. I wasn't sure if I could turn a FWD upper plenum around to fit if I had to go that route for MPI, and wtih the combined uncertainty and increased risk associated with a non-stock swap I decided to investigate TBI instead.
I called some local junkyards and found a 2.8 V6 throttle body, and that made me get serious. I went to the local bookstore and bought a book on GM fuel injection, which included a pinout of the computer. I had repaired fuelies before, and understood how they worked and what sensors were needed, so I made a list of all the sensors, parts and such I thought I'd need, and visited the junkyard.
The junkyard owner was skeptical about my idea, but didn't mind selling me stuff, so I got the throttle body, intake, EGR controller, distributor, engine-mounted fuel lines and filter bracket, and knock sensor for $100. I took the intake (at first I had hoped I wouldn't need it) because the bolt-pattern on a throttle-body is different than that of a carburetor. The distributor was for computer control of the timing (mine was vacuum advance), and my only real concern was that the bolt-pattern at the head-to-intake junction was different. I knew GM changed V8's when the went to center-bolt valve covers, but I didn't know if they ever changed the 2.8 V6.
I then acquired a MAP sensor for free, and a computer for $75 (including stock chip). I got the in-tank fuel pump assembly out of an S-10 of unknown engine size (including the pump itself) for $15. Additionally, my original charcoal canister had a half-dozen fittings, so I acquired one off of an '82 Camaro, which had only an "in" and "out" like TBI S-10s. For some unknown reason, GM ran a fuel and a return line on the carbureted 2.8 V6 trucks, so I didn't have to do any additional plumbing. I opened up my ASAP catalog and ordered a 10" AC Delco air cleaner, and a Painless Wiring TBI harness. I knew the TBI I had would take a 5" air cleaner (just like a V8) and since my original air cleaner wouldn't work, that seemed like a reasonable purchase. I was going to fabricate a harness, but couldn't find enough of a factory harness to get all the correct connectors.
The harness was for a V8 TBI system, but I was hoping that the famous GM interchangeability would save the day. I got the harness in, and opened my fuel injection book to the 2.8 V6 computer pinout. With my trusty multimeter I checked each pin in the harness against the book. To my surprise, almost every pin was right! The 2.8 V6 had three extra wires not found in the V8. The 2.8 V6 had an Elapsed Timer Module connected to one pin (fortunately I got this module when I got the computer), and two extra pins for EGR position information, which isn't used on the V8.
All that was left was the oxygen sensor. I spoke with a local exhaust shop, and followed his (excellent) suggestion. I took a spark-plug non-fouler and cut off almost all the external threads. He then welded this into my exhaust pipe. The O2 sensor (bought new from my GM dealer for $25) has a spark-plug thread, so this was great. The fitting, including installation, was $12.
After acquiring a fuel-pump relay, fuel filter, and gaskets, I was ready to start. Dad and I removed the carburetor, intake, distributor, AIR pump, fuel pump, and all emissions gadgets, and set them aside. A thorough cleaning later, we set the new intake in place, and hoped. It fit!!! Not long afterwards, we had the rest of the parts installed (including pipe plugs in the exhaust where the AIR system once resided). The harness was easy to install, and everything went well. The whole conversion took a weekend. We ran into only two problems.
The first problem was minor. It wouldn't start. We checked our connections, and everything looked right. The computer had no codes set, and the injectors were spraying fuel. So, I got under the truck so we could get a close look at the timing. I saw the timing mark go by, then another one. . . GM scribed three timing marks into the balancer, each 60 degrees apart. No problem, just reinstall the distributor and try again. This time, it ran great.
I took it for a test drive, and loved it. It felt like it had much more bottom-end, and a softer throttle spring made shifting smoother (that was probably in my head, but I did like it). After driving for a couple of days, though, my gas mileage was waaay off. Like 12 mpg. Sometimes, the truck would go way rich, too. When I started killing large spots of grass with leaking gasoline, I figured something was bad wrong. There weren't any fuel line leaks, though. After some investigation, I found that GM seems to have switched the canister and fuel-pump return lines between carbureted and FI trucks. I had connected the lines just like it was when the carburetor was on it, and assumed that the three lines were in the same order on the FI in-tank assembly as it was on my old one. Since the canister and return lines are the same size, it was an easy mistake. The fuel return line drops way down in the tank, and the vent for the canister sits at the top of the tank, with a shield over it so fuel doesn't go directly in. I was returning fuel to the top of the tank, and venting from the bottom! After switching the two lines, everything worked fine.
I now get 24-25 MPG on average, with much more bottom-end power, more overall power, and better drivability. The torque curve feels much flatter, facilitating smooth shifting. It is easier to start, especially if the truck has not been started in a while. The cold-weather drivability problems have almost completely disappeared.
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