A Timeline of Corvette Fuel Injection

Fuel Delivery Phases

Andy Bolig Jun 30, 2003 0 Comment(s)

The next step in the pursuit of fuel control arguably wouldn't be considered EFI, although it did open the door for electronics in fuel control. Beginning in the '80 production year, GM installed computer-controlled carburetors on those 305ci Corvettes bound for California. Earlier GM cars (non-Corvette) had the Computer Controlled Catalytic Converter (C-4) system that controlled only the air/fuel mixture by controlling the main metering rods inside the carburetor to allow better operation and efficiency of the catalytic converters.

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The '80 and '81 Computer Command Control system is an expansion of the C-4 system. The CCC system monitors up to 15 engine and/or vehicle operations for controlling up to 9 engine and emissions-control systems. In addition to regulating the air/fuel ratio, the CCC system controls spark timing, AIR management for optimum catalytic converter efficiency, and torque-converter lockup. Obviously, the Computer Command Control system was another step toward today's technology. The programming and computer hardware for the CCC system was nowhere near what is necessary for operation of today's Corvette, and the speed at which the processors operate in today's Corvette wasn't even dreamed about when the CCC system was first introduced. At that point, emissions concerns were the main reason for the evolution and reintroduction of fuel injection into the Corvette. The engineers at GM first had to learn how to keep the feds happy; only then could they devote their precious time to getting more power out of the engine. Lucky for us, performance and emissions are both part of the two-sided fuel-injection coin.

Squirters were back in '82, and this time they were electronically controlled. The tunability issues that plagued the earlier Ram Jets were being addressed by a computer. The Cross-Fire Injection (RPO L83) used two throttle bodies on top of the intake manifold. The computer to drive the system was based on a Cadillac DFI unit and worked with GM's Computer Command Control. CCC had been refined in '82 to the extent that it had the ability to make 80 adjustments per second, compared to the previous year's 10 adjustments per second. These advancements provided a mere 10 hp for Corvette, but it was the beginning of the upswing and it provided a quick means for getting fuel injection back into the Corvette until the Tuned Port Injection was ready for production.

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Cross-Fire Injection was carried over for the extended production year of 1984, and another 5 hp entered the engine compartment, topping off the Cross-Fire's engine horsepower rating at 205. History has proven that the Cross-Fire is a reliable design with the proper tuning and maintenance and, with some tweaking to the engine and fuel-delivery system, it can show a stock Tuned Port to the door. Due to its limited production, the Cross-Fire has a certain appeal for those who want more than "just another TPI Corvette." Whether you prefer the shark body style or the late-model (C4) body lines, you can get either with a Cross-Fire, since they were installed in the last sharks ('82) and the first late-models ('84). It may turn out to be the last engine that will ever have the privilege of spanning two generations of production.

Advancements in fuel delivery were coming fast. Within two production years, the Cross-Fire was shelved and replaced with Tuned Port Injection (TPI). The benefits of TPI were almost immediate. Horsepower increased to 230 at 4,000 rpm, and the torque numbers jumped to 330 lb-ft at 3,200 rpm. It was clear that GM was addressing performance and emissions concerns.

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Rather than rely on vacuum from the intake like the Ram Jet and Cross-Fire, GM began using MAF sensors on the '85 production models. This gives a better reading of exactly how much air is entering the engine and, in turn, how much fuel should be mixed with it. The '85-'89 TPI Corvettes use a MAF sensor to help regulate fuel, but in '90 they went back to using intake vacuum to regulate the amount of fuel the engine needed. Called "Speed Density," this new system calculated the engine load by sensing Manifold Absolute Pressure. The computer combines the MAP with the Intake Air Temperature and other engine parameters, such as volumetric efficiency and EGR rate, to calculate the mass of the intake air.

Another change that took place with '89 production was the elimination of the Cold Start Circuit that introduced additional fuel into the intake to richen the mixture under cold-starting situations.


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