11051 Wye Street
San Antonio, TX 78217


Website: http://www.InetWareTechnolgoy.com

Fuel Injection Specialties™ 2012

Fuel Injection Specialties

Telephone: 210.654.0774

Fax: 210.654.1444

GM Port Injection


The following information on GM Port Injection and GM Tuned Port Injection Systems has been compiled from GM published material and as a result of discussions with our technicians who have installed these systems on a variety of vehicles. It is to the best of our knowledge accurate.


The first production TUNED PORT INJECTION (TPI) appeared on General Motors vehicles in 1985. The GM vehicles built with these systems were Corvette, Pontiac Firebird & Trans AM, and the Chevrolet Camaro. These systems according to the manufacturer rendered up to 30 % improvement in Horsepower, torque and economy over carbureted systems, Independent laboratories conducted numerous tests on the TPI systems and indicated these claims were conservative and that increases of up to 35% in these three areas are attainable.

The 350/5.7L engines from the factory went from 205 HP (1984 Corvette/ crossfire injection) to 245 HP with the addition of TPI. The only differences were the addition of the TPI (1985) and improvements in the valve train (1987). Note that this is a 20% improvement over another proven form of fuel injection.

Several modifications have been made to the TPI system introduced in 1985. The 1985 system used a GM Part #1226870 ECM and had a Mass Air Flow (MAF) sensor and a MAFS module to control the power and burn off functions for the MAFS. In 1986 two relays replaced the MAFS module and the Electronic Control Module (ECM) was changed to a GM part #1227165. In 1989 the cold start injector was deleted from the system. The primary injectors were used for cold starts via a fuel enrichment program in the newer EPROM calibrators. In 1990 GM introduced the speed density system. In essence the MAFS was replaced with a Manifold Air Pressure (MAP) Sensor. This system uses an ECM GM Part #1227727 for the Corvette.

Another fuel system was introduced in 1992 called Central Port Injection (CPI) and appeared first on the 4.3L (W) L35 Engine. This system is the equivalent of TPI for the V6 and will increase horsepower and torque by a factor of 20% over TBI. A 30 % increase in horsepower, torque and fuel economy is seen over carburetion.

The LT1 was also introduced in 92, as the basic engine in the Corvette. It appeared in the Firebird, Z28 (F Body Cars), Caprice, Buick and Cadillac in 93. 1993 was the last year for EPROM's in these cars. Opti-Spark also made its entry on the LT1 engine in 92.

In 94, OBDII or EEPROM, computers were first used in the Corvette and F Body Cars. This was the 1st year for Sequential port Injection in these cars.

In 96 the LT4 appeared in the manual trans Corvette, it is rated at 330 HP and 340 lb ft torque. It looks the same as the LT1, however the heads and valve train have been modified. The valves are larger 2.00 Int / 1.55 Exh from 1.94/1.50. Air passages are larger to enhance volumetric efficiency, hollow valve stems, aluminum roller rocker arms and stronger valve springs have also been added. The camshaft has more lift and a slight overlap at the end of the combustion cycle eliminating the need for EGR. The compression ratio is (Premium Gas Only) 10.8:1 compared to the 10.4:1 LT1. This engine makes 330HPat 5800 RPM and 330 lb ft Torque at 4500 RPM.

We flowed the heads on both the LT1 and LT4. LT1's flowed 195 CFM compared to 240 CFM for the LT4.

Ported LT1's also flow 240 CFM. Porting the LT4 will render 272 CFM.

For 96 all Chevrolet engines are Sequential Port and are equipped with On Board Diagnostics Phase II (OBDII) PCM's. Sequential Central Port Injection is a standard on the 4.3L/4300, 5.0L/5000 L30, 5.7L/5700L31, and 7.4L/7400 L29 engines. What's nice about all this? They will fit the old engines, but heads would also have to be changed on the 4300, 5000 and 5700 engines.

Retrofit kits are available from FIS. For Example, Sequential Tuned Port Injection or Sequential Central Port, both systems are available from FIS.

Other Technological mods include Cam Sensor / Crank Pos Sensors in lieu of distributors. EEPROM Computers, Vortec Heads, Mass Air Flow Sensor, Roller Cams / Roller hydraulic lifters come with all engines. Retrofit kits are now available, from FIS, for Sequential Port Injection which will fit the SB, BB and the 90 degree V6 GM Engines.

Electronic Control Module (ECM)

The ECM's provided with the original equipment MPFI systems are indicated below:

Y=Corvette F=Camaro, Firebird, Trans-AM CK=GMC, CHEV trks

Power train Control Module (PCM)

The PCM is a programmable computer and does not contain a EPROM or calibrator as did its predecessor. The PCM contains a Electronically Eraseable Programmable Read Only Memory (EEPROM). This unit must be programmed before being placed in service. These Units can be re- programmed for any engine / transmission combination. All of these units are Sequential Port Fuel Injection (SEFI).

While each of these ECM's/PCM's will provide excellent performance for the Port and TPI systems, they are not interchangeable. That is a 1227165 will not plug in to a 1226870 harness and operate. The wiring for these systems is not interchangeable, without modifying the wiring harness. The LT1 PCM is not compatible with the earlier ECM's due to significant changes in the distributors of these engines.

The CK truck engines use a crank shaft sensor and camshaft position sensor to provide timing information to the engine.


The calibrator is a Programmable Read Only Memory (PROM) Chip which is installed in the ECM. It is this device that provides specific information for the ECM and allows for different timing characteristics, and injector pulse width for the 5.0L / 5.7L engines. A Calpak, a separate chip on the Calibrator Modules, normally provides the information to the ECM for rear axle gear ratio on pre 90 models. Information for the vehicle Anti Theft system, auto / manual transmission, and emission control system, typically resides in the EPROM. To allow for the various Engines, transmission, gear ratio combinations and to meet national, international and state standards for emissions, a wide variety of these Calibrators are available from GM. After 1987 some calibrators incorporate a vehicle anti theft system (VATS). The ECM will not fire the injectors until it receives the proper signal from the VATS module. The 1985 TPI calibration is contained in an EPROM (Erasable Programmable Read Only Memory) and is a 32K chip. The 1986-89 ECM contains a 128K EPROM, 90-92 ECM's use a 256K EPROM. The 94 Plus EEPROM is even larger. The factory ECM/PCM has a Learning capability which allows it to make corrections for minor variations in the fuel system to improve performance and drivability. There are two learning features. The Integrator and Block Learn (I and BL) and Block Learn Memory (BLM) cell. The I and BL feature is normal with a value of around 128. If this value is higher than 128, it indicates that the ECM is adding fuel to the base fuel calculation because the system is running lean, a value lower than 128 indicates that the ECM is taking out fuel because the system is running rich. The integrator is a short term corrective action while the BLM is along term correction. The BLM value will change if the integrator has seen a condition which lasts for a longer period of time. There are from two to sixteen different cells which the ECM modifies, depending on RPM, airflow or manifold air pressure and other conditions such as AC "ON" or "OFF", etc. The ECM learns how much adjustment is required in each cell, retains it in memory, and applies these adjustments when the engine operates in that cell or RPM - Load Range. These features of the OEM ECM allow the system to adjust itself AUTOMATICALLY to your engine and assure peak performance for stock and other than stock engines. When the vehicle power is disconnected for repair or to clear diagnostic codes, the learning process has to begin all over again. To TEACH the ECM, drive the vehicle at operating temperature with moderate acceleration and idle conditions. Performance Calibrations typically change the parameters for fuel flow, fuel cut-off and spark advance-timing and will allow increased fuel flow and modify the spark advance curves during rapid acceleration.

WHAT THE ECM - PCM DOES: The 1985-1988 TPI system utilizes the following sensors and devices to control the engine: Mass Air Flow Sensor, Manifold Air Temperature, Coolant Temperature, Oxygen Sensor, Throttle Position Sensor, Cold Start Switch, Cold Start Injector Fuel Injectors, Idle Air Control Valve, Distributor Electric Spark Timing, (Module in distributor TPI) Electric Spark Control, Module and Knock Sensor.

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 Disclaimer: “Many parts we sell are not legal for use on emission controlled vehicles and do not carry a CARB exemption number. They are intended for off-road or racing use only. A civil penalty of $2,500.00 can be imposed on the owner of a vehicle for each violation of the Clean Air Act. The only information to use to determine a product's status is written statements by the manufacturer of the products. Fuel Injection Specialties is not responsible for products and services it provides for racing or off-road use vehicles that may be driven on the street.”

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