The C4 Corvette era was from 1984 to 1996, and they were known collectively as the "Scientific Corvettes," according to automotive website edmunds.com. They were fuelled with the Crossfire Throttle Body fuel injection in 1984, but in 1985, fuel delivery changed to a Tuned Port Injected (TPI) system.
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Crossfire Throttle Body Injection (CFI)
The Crossfire Throttle Body Injection was introduced on the 1982 Corvette as the new fuel delivery system. It can be described as a cross between a carburettor and fuel injection. The first-edition C4 corvette in 1984 continued to use this fuel delivery system. The fuel pump was located in the tank. The GM specifications for fuel pressure was 9 to 13 psi; however, the recommendation was increased to 14 psi to eliminate occasional stumbling or if the engine wasn't getting enough fuel at about 4,000rpm.
Tuned Port Injection (TPI)
The 1985 C4 Corvette marked the introduction of the new Tuned Port Injection (TPI) fuel delivery system. The new, more-efficient induction fuel delivery raised performance to 230 horsepower with a better torque curve. The stock fuel pressure for 1985 to 1987 C4 engines with TPI was 36 to 39 psi with the fuel pressure regulator vacuum hose connected, and 47 to 48 psi with the vacuum hose disconnected. For the 1988 to 1996 C4 corvettes, the stock fuel pressure is 40 to 42 psi with vacuum hose connected and 47 to 48 psi with the vacuum hose disconnected.
Fuel Pressure Adjustment
The fuel pressure adjustment on both the CFI and TPI fuel delivery systems was crucial to maintain performance for the corvette. The electronic control module (ECM) computer was designed to deliver the correct amount of fuel based on the fuel pressure. If the pressure is too high, too much fuel will be delivered, and performance and economy will suffer. If the fuel pressure is too low, the car will be fuel starved, causing it to stumble and stall. Fuel pressure can be measured at the Schrader valve on the fuel rail with a fuel pressure gauge. Many of the original stock fuel pressure regulators were not adjustable. If fuel pressure is not within specifications, check the fuel filter, fuel pump and regulator in that order.
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