Tricks Of The Trade

Tuned Port Fuel Injection Retrofit

    TPI is today's most efficient fuel delivery system. Increased horse power, low fuel consumption, and low emissions result from the continuous adjustment of the fuel/air mixture and volume controlled by a computer throughout all engine temperature ranges and power demands. This process is achieved by a closed loop system made up of sensors continually responding to changing engine conditions. The sensors contain materials that react to a given task, ie., air temp, water temp, exhaust oxygen, and plenum vacuum. The reaction creates an amount of voltage resistance. With twelve volts going into a sensor, the resulting voltage return is monitored by the computer which dictates the amount of fuel flow. The oxygen sensor, located in the exhaust, (ill. 5), contains materials that create voltage instead of resistance, when reacting to heat and oxygen. The entire process or circuitry loop repeats in a fraction of a second.

Items needed: We deal with the folks at Street & Performance for all of our TPI needs. We new nothing about the history of our first TPI unit other than year built, so we sent it to them and asked for all upgrades, complete refurbish, the best new nozzles appropriate for our engine, and all necessary harness and parts for installation. Our first engine was a new 345 HO ZZ3 motor from Chevy. Street & Performance upgraded computer, etc to 1990 Corvette specs. Our upgrade included eliminating the 9th injector, (ill. 2) and replaced the air mass flow sensor with a MAP sensor, (ill. 6), on our early model TPI. Total Cost was about $2500.00. We knew a lot about our second unit and was told about $1100.00 would do it. It was well kept and mileage was under 100,000 miles.
    Early TPI's 1985-1986 will fit older Chevy engines. Chevy changed the angle of intake bolts from 1987 on. With some machine work to the bolt holes newer intakes will also work. Only GM gaskets should be used throughout. A constant 45-48 pound fuel pressure is required. Pumps are usually submirged in the tank, but external should also work. A fuel return line to the tank is also required. All fuel related connections must be done with flare or compression fittings. We used aircraft grade AN fittings combined with steel braided flex lines from Street & Performance to connect TPI to the Corvette steel lines mounted at the frame.

Begin by installing gas tank and fuel pump system, as mentioned above, two line system, 3/8 feed, 5/16 return and high pressure pump. The existing lines on our 1980 Corvette host car worked fine. Install the Street & Performance wiring harness, computer, diagnostic plug, etc. We mounted our computer behind the seat where Chevy did on '81 and '82 Corvettes, (ill. 4). Every connector on the Street & Performance harness is clearly labeled as to its placement. A wire labeled "12 volt while cranking" was eventually hooked up to the power side of the distributor, (ill. 2). Engine side of harness is led through the firewall and sealed with a boot.

TPI components are assembled to the engine piece by piece. When removing the old distributor be sure and make a chalk mark on the firewall where the rotor was pointing. If pointing forward keep turning engine until rotor points at the firewall. Install TPI intake manifold, (ill. 3), using GM gaskets, GM torque specs, and proper lubes and antifreeze sealant on the bolts as engine material type dictates, ie., aluminum heads require the use of sealant on intake bolt threads. Stick a long screw driver into the distributor hole and turn the oil pump shaft 1/8 turn clockwise. This returns the oil pump shaft alignment to where it was before the distributor was remove. Install the distributor, all the way down to the intake manifold. Fuel rails and regulator are then installed. Connect fuel feed and return lines. Fuel feed line connects to fitting next to Shrader valve, (looks like a tire inflate stem). Runners or air tubes, (ill. 2), are then installed. Important, Two runner bolts are accessed from the opposite side, (ill. 2), unlike all the others. Run nozzle, temp sensors, and idle air control motor wiring under fuel rail tubes. Secure these wires to fuel rail tubes keeping them up from resting on manifold. Nozzle wires are lead longest to front with green nozzle wires on left side. The air temp sensor wire is pluged into air temp sensor located at the bottom of the plenum, (ill. 2), while the plenum is being installed.

The MAP sensor, (Manifold Absolute Pressure), is installed on the right side of the plenum, (ill. 6), and is connected to the forwardmost of the two small fittings at the rear of the plenum. It is very important that its hose be no longer than eight inches from its source and not shared with any other device. Connect all other harness plugs occording to their labels. The speed sensor unit is joined to the speedo cable. Oxygen sensor, (ill. 5), is installed as close to engine as possible.

Start engine, check for fuel leaks. If engine doesn't start check fuel pump operation and pressure. Check distributor for spark and initial timing. Make sure that number one cylinder is firing on time. Number one cylinder is driver side forwardmost cylinder. To check for number one firing on time, remove left valve cover, (driver side), The rocker arm closest to the exhaust manifold chamber is the exhaust valve. The one next to it is the intake valve. Turn engine over and watch for the intake to go down then up. When it is totally up and the exhaust valve has not yet moved, the distributor has just fired number one cylinder. Lift distributor cap and make sure rotor is pointing to number one spark plug wire. If any doubt, trace spark plug wire to number one cylinder.

Set throttle position return voltage as per included instructions using a digital voltmeter and stabbing the wires with pins, (ill. 6). This setting needs to be precise, thats why analog multi-tester ohm meters are insufficient.

1. Completed TPI Unit

2. TPI Break Down

3. TPI Intake manifold

4. TPI Computer Installation

5. Oxygen Sensor Placement

6. MAP & Throttle Position Sensors

Work In Progress
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