Fuel Injection TPI, SFI, TBI, SPFI, MPFI LT1
The term has changed a bit over the years in this industry, fuel injection has revolutionized the way consumers, auto racers and hot rodders devour there horsepower. In the prehistoric Neanderthal era of street rodding and drag racing, consumers had no choice but to run the, over lathed piece of aluminum called a carburetor. True, pressure on earth has a weight of 14.7 PSI @ sea level and the turn of a screw on the high and low side along with a guesstamated, more timing, more fuel solves the drivability problem. The benefits of fuel injection everyone knows, will allow precise metering of the Air / Fuel Ratio, proper fuel usage, more timing on the lower end retarding on the top and overall more horse power. GM engineering of fuel injection didn't start in production vehicles till late 1983 -1984.
Cross Fire Injection (CFI) 1983-1984 L83 Two years Vette C3-C4 / One year F-Body) 205 HPThe fuel injection system was called Cross Fire Injection, as many hot rodders know of Throttle Body Injection (TBI ) cross fire was the first form of throttle body fuel injection. The dual throttle bodies lined up on the intake ports, in a cross ending manner. There was nothing special about the firing order, coil / ignition system or distributor, everything down to the combustion chambers were Gen I, old school style racer heads. The transmission of the corvette came in two options 700R4 or the standard 4+3. For those of you smart enough to stay away of this creation, you would never of had the pleasure of witnessing a bad concept, that stuck around too long. If you like this trans, the reason must be because you are stuck with it, in your 1984-89 Corvette. Take my advice, convert your 4+3 to a 6 speed. If you want to get technical, the only gears you could actually drive in were 1 through 4 the click the button on the top of the shifter and you have over drive, 5th gear. Since I have had the pleasure of owning this marvel, I want to rename it, to the 4 + 1 -1 +1 -1 +1. As you can see, if you drive you 4+3 in any city, you end up pushing the bloody hell out of this button.
TBI 1985-1995 204 HP 329 ft-lb Throttle Body Injection CK Chevy and GMC truck. You will find a creation of fuel injection known as Throttle Body Injection. This injection system in many opinions, to be the most reliable and self sustain design ever. Lasting 10 years makes this the longest and most successful engine and fuel injection design, ever to come from GM. The variation of sizes range from 4.3 5.0 5.7 and 7.4 liter servings. Pick your poison of any, check you power to weight ration and enjoy a reliable engine in any size, from this genre. The timing of this unit is a large High Energy Ignition (HEI) distributor, with a top mounted coil on the cap. In 1992-95 a new distributor design, that moved the coil to an external side mounted location, the new distributor known as Energy Ignition (EI) dubbed “Small distributor” was introduced that allowed a cleaner throttle response. The fuel metering is controlled by a basic Speed Density operation. Consisting of RPM from the distributor, Intake Air Temp (IAT) sensor to calculate the mass amount of air and the Coolant Temperature Sensor (CTS). The system also has the capability of meter the vacuum through the Manifold Absolute Pressure (MAP) sensor. The MAP sensor will adjust timing and fuel depending on load conditions, based on internal vacuum, In some situation the MAP sensor will adjust accordingly to altitude. The TBI engine 1986-91 was equipped with two transmission option a 700R4 or 5 speed. In 1992 the 4L60E transmission was available as well as the big dog 4L80E transmission, only for the ¾ and 1 ton truck.
TPI 1986-1989 MAFS 199 to 250 HP 290 ft-lb of torque. Tuned Port Injection era otherwise know as TPI was 1986 to 1987 F body 5.0 Liter, in 1988-1989 the 5.7 liter engine was available. The Y Body Corvette always had the 5.7 GM fuel injected engine. Transmissions available are the 4L60(No E, Vette ) 700R4, 5 speed and 4+3 (Vette). The air and fuel ratio of this fuel injection system was controlled by a very slow (to today’s speed of computers) but effective computer. Controlled by the 24 blade prom (program read only memory) in charge of the vital system info. In this section of the computer you will find start up enrichment, pulse width of injector, timing, fuel basically anything and everything the computer and fuel injection system can't live or run without.
There is another storage container in the computer known as volatile ram, here you will find engine drivability codes, diagnostic trouble codes (DTC). These can be erased when the tech removes battery power to the computer. The other section is called non-volatile ram, this is used for information that must stay, no matter what. Tuned port injection / Induction received its name because of the runners, as the air enters the throttle body, through the upper plenum, it is driven down a series of 8 runners that are all equally tuned, by length and size. Down to the lower intake port, thus the name was born Tuned Port Injection / Induction.
The firing order of the common V8 TPI is the same with the TBI fuel injection / crossfire fuel injection which is 18436572 rotating clock wise on the distributor. On all Speed Scene Wiring fuel injection wire harnesses, the right side (passenger ) intake manifold injector bank 2, 4, 6, 8, evens will have a Green wire controlling the pulsed ground to the injector. The left side of the intake (driver) injector bank 1, 3, 5, 7 odds, will have a Blue wire controlling the pulsed grounding of the injector. In this form of fuel injection there are only two (2) drivers that fire the odds and evens.
Drivers are a technical term meaning, a computer controlled operation typically operating solenoids or relays. The two drivers Blue and Green are again batch fire and fire the fuel injection system in batch intervals left right left right, bank one bank two, so on so forth. The injection on all Multi Port Fuel Injection systems of this time, have one injector per intake port / valve. The timer of this system, the distributor, was the large High Energy Ignition (HEI) a simple Hall Effect sensor, producing a 4 times and an 8 times signal, low reference and High reference signal providing the ECM with true reference.
For all intensive purposes all you need to understand about Hall Effect sensors are, they are magnetically based sensor with a digital clocker. With a metal rotor, driven by the distributor shaft, rotating through a semiconductor wafer, once converted producing a cycling digital (Hz) signal. The veins on the rotor represent how many cylinders are in the engine.
The reason why these types of sensors are so accurate is, there digital. No peaks and valleys like alternating current, just 0 or 1, ON or OFF. Computers communicating need no buffering to accept the signal, the ON and OFF operation make this perfect for controlling ignition components. The last technical note is, the signal voltage does not vary with vehicle speed, so the computer or circuitry will never need to search for a trigger leveling of end voltage. The 1986-89 TPI fuel injection system could measure the mass (Mass Air Flow Sensor) amount of air coming in the engine as well as the temperature of the air via through the Intake air sensor (IAT) The coil on the large HEI was mounted on the top of the distributor cap. With the lack of a Manifold Absolute Pressure sensor (MAP) the engine had no way to calculate vacuum pressure. This sensor can calculate and move / monitor all the way from perfect vacuum (21KPA) down to total garbage-gobbler 8kpa, at that reading, your lucky if you can even move the vehicle.
TPI 1990-1991 Speed Density Tuned Port Injection systems of this year are dubbed with the name Speed Density. The transmission choices are 4L60 (No E, Vette) 700R4 (F-body) 6speed (Vette) 5 Speed (F-body) The distributor of this year was a small EI (Energy Ignition) system that sported an external coil. The meaning of the name Speed Density is composed of the simple truth. The metering air capabilities are based on speed from the EI distributor being RPM, temperature of the incoming air and temperature of the coolant. The IAT is left to modify mixture values. Along with a good base idle, the Idle Air control Valve (IACV) supplies a controlled vacuum leak, allowing the engine to idle smooth. In the older 1985-89 TPI computer, the fuel injection system could measure the mass amount of air coming in the engine as well as the temperature of the air. The speed density system is a solid performer, if left stock, a great performer in water / wet off road application simply because there is no Mass Air Flow sensor to short out.
CPI (Central Port Injection) 1991 to 1994 Chevy and GMC trucks, 175 to 195 HP / 260 Ft-lb of torque.. With the injector pack / Injector assembly centrally located in the fuel injection manifold, the runner tubes route into the intake ports, from a central location. Thus hitting the various intake ports, on the cylinder heads, the tuning valve regulates the air flow depending on rpm, Manifold Absolute Pressure (MAP) and Throttle Position Sensor (TPS) to open the valve to full flow. The first Central Port Injection fuel injection intakes 1992-93 had this valve controlling the full flow of the air in the fuel injection intake, excluding the Cyclone and Typhoon models. This type of injection is a batch fire, speed density, fuel Injection. Many may consider this the TPI fuel injection system for the V6, because of the fuel metering control and the runner configuration.
1992 LT1 (Corvette) 1993 (F-Body) Speed Density fuel injection system, was a great concept with 275 to 297 HP and 304 ft-lb of torque, made this the most powerful injected engine in GM small block production history. The operating system was Speed Density, meaning all metering of the fuel injection was based on the RPM, Manifold Absolute Pressure (MAP). Throttle Position Sensor (TPS) and Engine Coolant Sensor (ECT) and the Intake Air Temp (IAT) to play cleanup better, kept the AFR (Air Fuel Ratio) in check. The 8 Injectors are batch fire controlled, giving this 350 CID 5.7 liter injected engine optimal drive-ability. The fuel injection configuration on this engine was Multi Port Fuel Injection MPFI, with Bosche injectors that have a set range of 16 Ohm. The distributor is a Hall Effect style ignition system, which is located behind the water pump. The coil and module are located on the right side, passenger top right, Corvette engine. The coil on the F-Body is on the left, passenger side of engine. One of the unique visual dominating factors in determining if you have a Corvette engine or F-Body will be the brackets. The Corvette has all of the accessories (Alternator, A/C compressor) on the Left side driver. The F-Body will have the alternator on the right passenger, A/C on the passenger right and the electric air pump on the left. The fuel rail on the intake will not have a crossover tube in the front intake, behind the throttle body, the crossover and supply is located in the rear. The firing order on the LT1 1992-93 was 18436572 which are the same as the old school V8 TPI, TBI and crossfire. The distributor is non-vented, so keep this engine away from water.
1994-1997 LT1 MAFS ( 96 the last year for the Vette) F-Body last year was 1997 LT1 fuel Injection. With all of the above being the same, the addition of a faster Intel based, “Flash” computer processor and the Mass Air Flow Sensor (MAFS). The final adaptation of old theory was erased once the Multi Port Fuel Injection became Sequential Port Multi Fuel Injection (SPMFI). Throughout the next 3 to 4 years the distributor went from non-vented to vented in 1995, with three different timing cover designs and three different distributors from 1992-1997. Speed Scene Wiring can help you acquire the parts you need based on your info. In 1996-97, F-Body the LT1 fuel injection system gained another Hall Effect sensor, known as the Crank Shaft Sensor (CKP). This sensor would just make timing even more precise, which relates to more horse power and better fuel economy / controls. In 1996 the operating system went from ODBI (On Board Diagnostic One) to OBDII (On Board Diagnostic Two). These are the standards, before global organization and federal control for all manufacturers. And after total federal control, with standard of communicating language for all cars in the US. OBDIII soon to come will be big brother, this system will notify you with a set amount of time to fix the manufacturer related problem. If you are not compliant you may find your vehicle or yourself in violation of federal laws / code. The 1996-97 fuel injected LT1 went from 2 heated o2 sensor, to 4 heated O2 sensors, 2 pre heated and two posts heated sensors. In the 1994 Corvette the introduction of the 4L60E transmission was a success, this transmission is basically a 700R4/ 4L60) with an electronically controlled solenoid valve body.