C4 Fuel Injection Overview

By Chris Petris

Speed density was the first fuel control system used on 1982-1984 Corvettes. It was also used on the 1990-1993 cars. Speed density uses a manifold absolute pressure sensor (MAP sensor) to calculate the necessary fuel load. The 1990-1991 cars have a MAP sensor bolted directly to the intake plenum. The 1992-1993 cars have the MAP sensor bolted to the intake manifold. The throttle position sensor, coolant temperature sensor, and intake air temperature sensor are also used to calculate fuel.

Mass-air flow fuel control was introduced in 1985 and used until 1989. It was reintroduced in 1994 along with sequential fuel injection. The 1985-1989 mass-air system had a few changes along the way.

1985 cars have a slower baud rate computer and use a mass-air sensor module to control burn-off and to power the mass-air sensor.

1985-1988 cars use a stand-alone cold-start system that requires intake manifold porting to allow cold start fuel flow. This porting hurts power output.

1989 cars had no cold-start system, along with intake manifold porting changes. The 1989 cold start event is handled by the PROM (chip). The fuel injector pulsewidth was increased. 1986-1989 computers were replaced with a faster baud rate unit.

1994 cars have an On Board Diagnostic (OBD) system (first generation). The OBD system was introduced to bring diagnostic uniformity to all makes and manufacturers. The 1994-1996 OBD computer system utilizes mass-air and MAP sensors to control fuel delivery. The 1994-1996 cars utilize sequential fuel injection, which means fuel is injected only when needed. These cars have better fuel control and respond better to high performance modifications.

The 1995-1996 cars have OBDII fuel control systems that follow more stringent fuel emission control standards. Catalytic converters have oxygen sensors checking their performance as well as controlling fuel in closed loop.


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C2, C3 & C4 A/C Retrofit

By Chris Petris

Basic System Operation

The compressor pressurizes the refrigerant then it enters the A/C condenser as a gas. The high temperature, high pressure gas is cooled as it goes through the condenser. This changes the gas to a liquid. Then the liquid goes to the evaporator through an expansion valve or metered orifice. This quickly depressurizes the liquid. This vaporizing liquid lowers its temperature rapidly. The vaporized refrigerant returns to the compressor (the compressor cannot handle any liquid).


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C2 & C3 Troubleshooting

By Chris Petris

The most important tool to use when troubleshooting is a good memory or notes. If necessary, write down as much information as possible. This will help compile a troubleshooting notebook. A factory service manual is an invaluable tool when diagnosing problems. A road test is very important and notes should be taken then also. When road testing I take notes about when a problem occurs: hot engine, cold engine, or possibly after a hot restart. In the shop I try to get as much information as possible about any previous repairs and parts that were replaced. A simple audio test of the engine’s performance is to listen to the engine cranking over and note any irregularities. A V-8 engine that has comparable compression on all cylinders has an even rhythm as it cranks over. If you hear what sounds like a rhythmic increase or uneven pulses during cranking, most likely a cylinder(s) has low compression, which may be caused by a burned valve or possibly a hole in a piston.

I would perform a crankcase pressure test. A crankcase pressure test consists of removing the PCV valve and breather tube on an engine that is at operating temperature. Watch for oil vapors coming out of the PCV valve port. If you have oil vapors coming out of the PCV valve port in pulses like a steam engine you have broken piston rings or possibly a broken piston. A light amount of smoke (blow by) without rhythmic pulses is normal on high mileage engines. If I find either excessive blow by or uneven cranking I do a compression test first, then a cylinder leakage test. The most important thing is to have good engine compression with minimal blow-by before proceeding.


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C4 Interior Overview


By Chris Petris

The C-4 interior is comprised mostly of plastic. The 1984-1989 dash carrier is made entirely of plastic. All of the plastic dash fascia can be damaged quite easily just by over-tightening the screws. I use a screwdriver or a clutch-operated power screwdriver. When using a clutch-operated screwdriver, be sure to use the lowest setting to avoid cracking the dash fascia. Then use a Phillip’s head screwdriver to check for tightness. A cordless drill with a Phillip’s head bit is a good idea for removal only; definitely use a screwdriver when tightening. Early cordless drills did not have any torque setting options. They require extreme care if used for any dash screw tightening.

The light switch area of the dash carrier typically cracks when this occurs a rattle or creaking noise will be heard that is difficult to locate. I repair these by fabricating a reinforcement plate using a piece of .020 gauge aluminum. The light switch stud nut and the dash carrier mounting 13mm stud nut must be removed to fabricate and install the reinforcement plate. The light switch shaft will have an outer nut holding the light switch to the dash, which will be referred to as the light switch stud nut. This can be removed with a special socket or a pair of snap ring pliers. A pair of needle nose pliers will work in a pinch. A paper file folder can be used to make a pattern- and save a lot of aluminum. A file folder is thicker than paper but cuts easily with scissors this will allow you to cut out the holes for the light switch stud nut and the dash carrier mounting stud. Make sure the reinforcement plate pattern covers the entire cracked area. Now transfer the pattern over to the aluminum plate. Then drill a 7/16” hole in the lower corner of the reinforcement plate for the light switch shaft. Next drill a 3/8” hole in the upper corner of the reinforcement plate for the dash mounting stud. I use a good quality epoxy to bond the reinforcement plate to the dash carrier. The reinforcement plate and dash carrier must be cleaned carefully and free of all oil. Isopropyl alcohol or automotive brake cleaner spray will remove any oily residue. After applying epoxy to the reinforcement plate I install it over the light switch shaft and dash carrier mounting stud. Tighten the dash carrier mounting nut. Install the light switch stud nut into the light switch. Then I like to put two 1/8” rivets in the reinforcement plate to keep it tight until the epoxy sets up avoid riveting in the cracked area. I have only seen one, possibly two cars that did not have a badly broken dash carrier, so look for this during a dash restoration.


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Corvette Glossary of Terms

For your convenience, the following is a glossary of terms commonly used in the Corvette community.
Anti-lock Braking System.  Sensors monitor wheel rotation and prevent wheel lockup during braking by modulating hydraulic pressure.

Acceleration Slip Regulation

The post section between the door glass and the windshield.

The pillar between the door glass and the rear window.

Big Block
Large displacement engines (396, 427 and 454 cubic engines), produced at the Tonawanda, NY engine plant.  Optional in Corvettes from 1965 through 1974.

Bloomington Gold
A major Corvette show and gathering held annually since 1973.  This popular annual Corvette show is known for its certification judging system based on factory originality.  Held in Bloomington, Illinois from 1973-92, then in Springfield, Illinois since 1993.

Blue Flame
The name of 235ci 6-cylinder engines between 1953 and 1955.

Bowling Green
Home of GM’s Corvette assembly plant and the National Corvette Museum.

C1 thru C6
Terms used to classify Corvette generations based on body styling.
C1: First generation of Corvette (1953-1962).
C2: Second generation of Corvette (1963-1967).
C3: Third generation of Corvette (1968-1982).
C4: Fourth generation of Corvette (1984-1996).
C5: Fifth generation of Corvette (1997-2004)
C6: Sixth generation of Corvette (2005-current)

Performance tuning company based in Old Lyme, CT.  THeir highly modified C4 models are often called “Callaway Twin Turbos”.   Available through Chevrolet dealers since 1987.

Annual Corvette show in Carlisle, PA.

Cubic inches.  To determine, multiply the volume of the space through which the piston head moves in the full length of its stroke by the number of cylinders in the engine. The result is given in cubic inches.

A Corvette with a fold-down soft top. Term “roadster” was used for the 1953-1955 Corvette.

Annual Corvette show at Cypress Gardens, FL.

Duntov Award
The highest award of the National Corvette Restorers Society (NCRS), named for Zora Arkus-Duntov Legendary chief engineer, called “father” of the Corvette.

Factory Optional Accessory.

The fuel-injected Corvettes of 1957 through 1965.

4 + 3
Four-speed manual transmission with 3 overdrive gears available from 1984-88.

Gold Certificate
Top Bloomington award for factory originality.

Gold Line Tires
Tires with gold striped sidewalls optional in 1965 & 1966.

Independent Rear Suspension.  In the Corvette, the conventional live-axle suspension system was superseded by IRS in 1963.

Knock Offs
Optional cast aluminum wheels available from 1963-66.

The base C3 350 cubic inch engine

The optional higher output C3 350cubic inch engine (1973 – 1980).

Engine used from 1986 until the LT-1 came out.

Limited Production Option

Designation of the second-generation small block Chevrolet V8 used in 1970-72 & 1991-96

The successor to the LT-1, used only in 1996

The overhead cam 32-valve ZR-1 engine, built by Mercury Marine.

Term used for the high performance 454 offered in C3 Corvettes, and later the high performance engine used in the C5 Z06 Corvette.

M20, M21
Muncie 4-speed transmissions used in early Corvettes.

Another Muncie 4-speed, known as the “Rock Crusher”.

Mid Year
Designation for the C2 generation of the Corvette (1963-67).

Multiport Tuned Injection.  Fuel injection system used from 1992 on.

New Old Stock, dated but un-used parts.

Pace Car
Limited edition replicas of the Indy 500 pace cars offered in 1978 and 1986.

Red Line Tires
Tires with red striped sidewalls optional in 1967 & 1969.

Corvette convertibles. Term “roadster” is used esoterically for 1953-55 Vettes.

Regular Production Option

Side Pipes
Optional side mounted exhaust pipes offered from 1965-67  and in 1969.

Silver Anniversary
Limited edition two-tone silver paint option offered in 1978 to commemorate the 25th anniversary of the Corvette.

Small Block
Engines produced with 265, 283, 305, 327 and 350 cubic inches.

Solid Axle/Striaght Axle
Solid axle Corvette produced from 1953-62.

Split Window
Term used to describe the 1963 Corvette hard top coupes because of the split rear window.

Sting Ray
Designation and logo of the 1963-67 Corvette.

Designation and logo of the 1969-76 Corvette.


A Borg-Warner 4-speed transmission used after the Muncies.

Split removable roof panels from 1968-1982.

TH400R, TH700R4

4-speed automatic transmissions (3-speed w/one overdrive gear).

TPI (Tuned Port Injection)
Fuel injection system used from 1985-91.

Turbo 350
3-speed automatic transmission used by GM.

Turbo 400
Three speed automatic transmission built with higher tolerances than the 350 and with different gear ratios.

Vehicle Identification Number.  Used to designate options and production sequences on all cars.

The area between the seats of 1953-1962 and 1997-1999 model years of Corvette
which cascades down from the rear deck and sports the Corvette emblem.

The term used by General Motors to designate the automotive platform upon which the Corvette sports car is built. The Corvette has been a “Y-Car” since it’s inception in 1953. Prior to 1953, the Y-car designation was used to denote experimental platforms and models. The most notable were the Buick Y-Car’s, which were inspired by Harley Earl.

Special 2001-04 performance Corvette featuring 385-405 horsepower and enhanced suspension and braking components.  Available only in the hardtop model.

The ZF-6 speed transmission used since 1989.

Special high-performance package optional from 1990-95 with special 32-valve overhead cam engine. Also, the LT1 Special Purpose Engine Package offered from 1970-72.

The LS6 Special Purpose Engine Package offered from 1970-72.

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