Mention fuel injection to the average hot rodder and his head immediately fills with visions of late-model Corvettes, tuned-port plenums, multiport injectors, and big bucks. If your brain works that way, it's time to reprogram your gray matter. You see, there's a low-dollar alternative to TPI fuel injection for Chevy small-blocks, one that provides the same improved driveability, fuel-economy, and performance at a fraction of the cost. Meet Mr. TBI, throttle-body injection, also known as the carburetor with a brain. TBI systems use a dual-plane aluminum intake manifold and a throttle body with two injectors that deliver fuel to the engine.
The Painless Wiring TBI fuel-injection harness has everything needed to connect your system. The instructions are comprehensive and include a complete list of all parts and the GM part numbers.
TBI has been standard equipment on millions of GM pickups and sport/utility vehicles since 1987, so the components are common, proven, and bulletproof. TBI also emphasizes low-end torque-good news for any street rat. And if you convert from carburetion to a TBI system, all the small-block's existing bracketry for the alternator, A/C compressor, and power-steering pump can be retained-not true for TPI systems.
We recently converted a '48 Ford sedan running a four-barrel-fed 327 small-block to TBI using stock GM parts and a wiring harness from Painless Wiring. While TBI components can be found at wrecking yards and swap meets, we opted for a ready-to-go package from Arizona TPI Specialists in Tempe, Arizona, which specializes in GM fuel-injection systems. Arizona TPI and Painless Wiring base their systems on TBI units from the '87-'90 GMC/Chevrolet pickup or Suburban. In fact, the Painless Wiring harness will work only with computers from these vehicles. This assembly retails for approximately $1,600. Careful boneyard scrounging could net all the major pieces for hundreds of dollars less.
On this throttle body, the injectors alternate so that each injector opens every other time a spark plug fires. Injectors can go a lifetime without needing to be rebuilt.
A TBI shopping list includes the following: a TBI throttle body and intake manifold, an electronic control module (ECM), a GM electronically controlled distributor, an electric fuel pump, a fuel filter and a pressure-safe post-pump filter, a fuel return line to the tank, a manifold absolute pressure (MAP) sensor, an electric-spark control module, fuel pump relay, coolant temperature sensor, knock sensor, oxygen sensor, an oil-pressure switch, a vehicle-speed sensor, and a wiring harness.
The conversion is very straightforward. You swap intake manifolds and distributors, install all sensors, mount the fuel pump and fuel lines, route and connect the wiring harness and computer, and turn the key. Still, there are a few caveats...
Every fuel-injected GM small-block uses a feedback distributor, as do some mid-'80s Camaros and Firebirds with computer-controlled carburetors. Later models mount the coils separate from the cap. Note the four-pin connector. Boneyard price: $40 to $100.
In stock configuration, GM locates the fuel pump inside the tank. But the pump-a high-speed vane-type that spins at 3,500 rpm-can also be mounted outside the fuel tank. Since TBI systems run at a low pressure, between 9 and 12 psi (compared to 35 psi for TPI systems), a "soft" fuel return line can be used. To plumb the return line to the tank, we installed a trick fuel-gauge sending unit from Classic Instruments that uses a return tube as the float mechanism's mounting stanchion. It simply slips into the mounting hole for the stock tank sending unit.
The heart of any fuel-injection system is the wiring harness. The Painless Wiring harness pre-connects all TBI sensor connectors-each is unique to the sensor it feeds. Routing the harness is time consuming and contingent upon where the computer is placed. We hid the '48's ECM under the dash between the A/C evaporator and the fuse panel, but the kick panels are a good spot, too.
The GM throttle body and manifold assembly looks a lot like a carb setup.
The Assembly Line Diagnostic Link (ALDL) connector deserves special mention. This small 12-pin connector is the window to the ECM's memory. Painless mounts the ALDL on a bracket fitted with a small "check engine" light. This light comes on when the ignition is turned on and goes out once the engine fires. If there is a problem in the system, it stays illuminated. If the problem is short lived, the light goes out, but the ECM stores the info in memory. To find out what happened, jump two terminals on the ALDL, and the check-engine light flashes the codes. Yes, TBI talks to you. Then you simply fix the problem. Try that with a carburetor.
On the road, the fat-fendered Ford we converted demonstrated crisp throttle response, strong acceleration, no flat spots, and zero cold-start stumble. To start a cold engine, simply turn the key: The engine fires immediately and idles smoothly. On the road, fuel demand is down, and driveability is up. And re-jetting for changes in altitude is a thing of the past; the computer adjusts the fuel mixture and ignition timing on the fly.
The ECM for a '87-'90 GM pickup truck or Suburban (PN 1227747) with a 5.7-liter (350ci) engine is the ONLY one that will work. Boneyard price: $75 to $100.
There you have it-a quick primer on TBI fuel injection. To completely describe all the nuances and technical background of fuel injection would take a book. Therefore, we recommend two such manuals: How to Tune & Modify Chevrolet Fuel Injection by Ben Watson and Hot Rod Wiring by Tim Remus and Dennis Olverholser. Both are available from Motorbooks International.
