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General Motors introduced TBI—throttle body fuel injection—in the mid-1980s. This story shows how to adapt TBI fuel injection to any small-block Chevy. While fuel injection scares many shade-tree mechanics, it shouldn't. It's not as complex as you think, and the benefits are surely worth the trouble to figure it all out. To prove our point, we recently converted a '48 Ford sedan running a 4-barrel-fed 327 small-block to TBI using stock GM parts and a wiring harness from Painless Performance. A brave new world beckons.

What's TBI?
TBI uses a standard-appearing intake manifold and a "throttle body" with two injectors that squirt fuel into the manifold. Think of it as a carburetor with brains. While tuned-port fuel injection (TPI) gets all the press, TBI delivers the same improved driveability and fuel-economy benefits. TBI systems have been standard equipment on millions of GM pickups and sport-utility vehicles since 1987; the components are proven and bulletproof. TBI also emphasizes low-end torque—good news for any old-truck owner or hot rodder. And if you convert from a carb to TBI, all existing bracketry for the alternator and A/C compressor can be retained.

How EFI Works
Electronic fuel injection (EFI) is simple in concept: Sensors send information on various engine functions—vacuum, throttle position, exhaust, vehicle speed, coolant temperature—to a computer. The computer kicks all this data around its circuit board for a millisecond or so, then tells the fuel injectors and distributor how much fuel and timing to deliver. The result is an engine that receives exactly what it needs when it needs it, thus performing as efficiently as possible.

What's TPI?
These days, quite a few small-block Chevy-powered conversions run GM tuned-port (TPI) fuel injection, yanked off a Camaro or Corvette. TPI uses an individual fuel injector for each cylinder and a swoopy air plenum and runner. TPI is a logical, costly option for rodders seeking high-rpm power and an engine bay that looks like the business end of the space shuttle.

Conversion List
A TBI fuel injection system requires the following components: A TBI throttle body and intake manifold, a computer (a.k.a. ECM; electronic control module), a GM electronically controlled distributor, an electric fuel pump, a fuel filter, one pressure-safe post-pump filter, and a fuel return line to tank. Also required is a MAP (manifold absolute pressure) sensor, an electric spark control module, fuel pump relay coolant, a temperature sensor, a knock sensor, one oxygen sensor, an oil pressure switch, a vehicle speed sensor, and wiring harness.

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Photo Guide

Painless Wiring supplies a threaded oxygen-sensor boss to be welded into the exhaust system. It must be mounted within 12 inches of the exhaust port for the sensor to work correctly.

The vehicle speed sensor attaches between the transmission and speedometer cable. It tells the computer (ECM) the relative speed of the car.

The Painless Wiring TBI fuel injection harness includes everything you need to connect your system. The comprehensive instruction manual includes a complete list of all parts required, with GM part numbers.

This is the ALDL connector and Check Engine light. It's where you tap into your computer's diagnostic power. The computer stores trouble codes in memory, which are communicated via flashes by the light.

Painless Wiring identifies every wiring circuit and connector with small plastic flags. Do NOT remove these tags until you're finished!

The brains of the outfit: the ECM or computer. ONLY use the ECM for a 1987-90 GM pickup truck or Suburban with a 5.7L (350ci) engine. Required part number is 1227747. Wrecking yard price: $75-$100.

GM fuel injection systems require a compatible, electronically controlled distributor. Every fuel injected small-block uses this distributor, as well as some mid-'80s Camaros and Firebirds with computer-controlled carburetors. Later models mount the coils separate from the cap. Note the absence of a vacuum advance can and the addition of a 4-pin connector. Wrecking yard price: $40-$100.

The oxygen sensor reads the content of exhaust oxygen, thus measuring the leaness or richness of fuel mixture?keeping the engine running with a 14.7:1 air-fuel ratio.

On the left is the all-important MAP sensor (manifold absolute pressure), which reads manifold pressure, thus engine load. It should be mounted within 12 inches of the throttle body, above the vacuum source. On the right is the Electronic Spark Control, which feeds the distributor key data.

The GM throttle body and manifold assembly looks a lot like a carb setup.

This GM throttle body has two "bottom-feed" fuel injectors. On two-injector applications, injectors alternate so that each injector opens every other time a spark plug fires. Injectors can go a lifetime without needing to be rebuilt.

Arizona TPI supplied this fuel pump/filter/mounting kit. A pre-pump filter MUST be used?any small piece of grit or hose can damage the pump. The post-pump filter MUST be designed for fuel-injection systems, as it is under constant pressure. The pump is wrapped with foam to keep its vibration from being heard inside the vehicle.

When using a TBI intake manifold on early-style small-block cylinder heads, the center bolt holes must be machined/elongated because they go into the head at a different angle. Arizona TPI supplies manifolds already machined, ready to go.

For leak-proof fuel line plumbing, we used Aeroquip Versil-Flare flareless tube fittings and Aeroquip AQP Socketless hose and fittings. AQP hose and fittings are good for 250 psi?yet don't require any hose clamps.

Fuel return-line plumbing was made easy with a Classic Instruments fuel sender (p/n SN33), which uses tubing to mount the float/sender mechanism. We added a 90-degree fitting so the fuel line would fit between tank and trunk floor.

Mounting the vehicle speed sensor to the Turbo 350 tranny was complicated by lack of clearance inside X-member. The solution: a short, 4" cable extension that positioned the VSS outside the X-member.

The throttle-cable and transmission kickdown cables are from Lokar Performance Products. Mounting is a bit tricky because TBI doesn't use the standard carb-pattern 4-bolt mounting. We fabricated a bracket/riser that bolted to an extra threaded manifold boss.


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