In 1985 the first production TUNED PORT INJECTION (TPI) appeared on General Motors vehicles. 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 labratories conducted numerous test 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 burnoff 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 a ECM GM Part #1227727 for the Corvette and 1227730 for Camaro.
ECM - Electronic Control Module The ECM's provided with the original equipment TPI systems are indicated below:
Model Year GmpartNo Engine
F,Y 1985 1226870 5.0L/5.7L
F,Y 1986-1989 1227165 5.0L/5.7L
F 1990-1992 1227730/16198262 5.0L/5.7L
Y 1990-1991 1227727/16197128 5.7L
Y 1992 16159278 5.7L LT1
F 1993 16159278 5.7L LT1
Y=Corvette F=Camaro ,Firebird, Trans-AM
Chips/Proms The chip 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 a EPROM (Eraseable 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 driveability. 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, dependingon RPM, airflow or manifold air pressure and other conditions suchas 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 allows 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 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) Electric Spark Control, Module and Knock Sensor. When the starter is engaged and the coolant temperature is less than 100 deg F. The cold start injector provides a spray of fuel, of 8 seconds duration max, to each cylinder via a air distribution system built into the intake manifold. If the engine temperature is greater than 100 deg F, the cold start injector is disabled by the cold start switch. Upon startup the ECM utilizes information in the calibrator to establish the initial pulse rate for the injectors and the engine starts. At this time the engine is operating in open loop mode and will continue to do so until the engine warms up. After the warm up period the ECM scans the sensors, if all sensors are operating and within their proper range, the engine then goes into closed loop operation. This means that the sensors are dynamically controlling the engine. In the event the information received is higher or lower than the normal range, a code will set in the ECM, and the Check Engine or Service Engine Soon light will come "on". The ECM receives information on air flow, engine temperature, air temperature, exhaust gas oxygen content and throttle position. This information is used to calculate the proper pulse width for the injectors and fires the injectors for the calculated period. This procedure is repeated continuously in very rapid sequence to maintain the optimum fuel air ratio. The electronic spark control components provide maximum advance, if engine knock is detected the spark is automatically retarded. This too, is a continuous process. It should be noted that the following components are MATCHED for optimum performance; Distributor - EST module, ESC module, knock sensor and ECM calibrator. These components are not interchange able between 5.0L - 5.7L engines. 5.7L components referenced are recommended for 327 - 400 CID engines. 5.0L components are recommended for 265- 305 CID engines.
In 1989 the cold start injector was deleted. The calibrator provides a wider pulse width on startup to provide a richer mixture for a cold engine. All other features are the same.
In 1990 the MAF was replaced with the MAP sensor. The1990-92 TPI system still operates the same except that Manifold AirPressure is used to calculate injector pulse width as opposed to airflow. The 1990-92 TPI system also uses a more sophisticated VATS system to disable the injectors. A resistor is embedded in the ignition key. The resistance is read by a VATS module (Camaro, Firebird and Trans AM) or a Command Control Module (CCM) for the corvette. If the key is the right resistance a signal is sent to the ECM enabling the injector circuit. If the sequence or the resistance is not correct, the engine will not start. All other sensors are the same except that the TPS is no longer adjustable. The only adjustment is idle control, and this too is factory set.
Induction The 1985-86 intake manifolds will fit the older small block heads without modification. In 1987 and up, the heads were designed with vertical bolt taps for the two center bolts on both sides of the intake manifold. With a little drilling the newer manifolds will fit the older style heads. The intake manifolds are therefore interchangeable for all small engines. The plenum is interchangeable for all model years thru 1990. The 1990 and up have tapped holes for the mounting of a MAP sensor (right rear of plenum). The throttle body is different on 90 and later models, modifications can be made to the plenum to use the 90+ Throttle Body by drillling a hole in the front of the plenum. Intake tubes (runners) are interchangeable for all model years, however the left intake tube through 1988 has a mounting for the cold start injector, for 89 and up this mounting is deleted. NOTE: Throttlebodies 85-88 are the same and must be matched to plenums 85-88. To work properly on 90 and up plenums a hole (1/2") must be drilled, between the intake openings where the throttle body mounts, to allow for passage of idle air from the IACV to the plenum. 89 and up throttlebodies will work on earlier plenums without modifications. The fuel rails have a few differences. If the left side fuel rail has a fitting at the end close to the firewall it is from a 1985-88system. The fitting is for connection of the cold start injector fuel line. The left side fuel rail is stamped at the factory to identify same with the engine. The Fuel Rail Identification Table above will assist you in identifying your system as a 5.0L / 5.7L and the injectors furnished with those systems.
Distributors All 85-86 systems used a GM HEI distributor. The connector for the distributor is keyed differently than previous model years. 87-92 systems use a small diameter distributor with an external coil. 87-91 Corvette's still use the HEI distributor. Either distributor will work, however the connectors are different.We can furnish adapters to make them interchange. The HEI Distributor for the 85-86 5.0L engine has the number 1103679 stampedin the aluminum casting at the base of the distributor. The 85-91 5.7L HEI unit is stamped 1103680. The smaller diameter (72mm) distributor is stamped 1103479 on the metal plate beneath the distributor. The72mm Distributor was furnished with 5.0L/5.7L engines on the Camaro,and Pontiac engines 87-92.
Fuel Pumps The OEM fuel pump for TPI is an "in tank" fuel pump with an operating rating of 50 PSI and 24 GPH. This pump is recommended for all vehicles with in-tank pump mountings. It is important to note that Throttle Body Injection systems operate at 12 PSI. Almost all carbureted systems operate at low pressure utilizing a mechanical pump. An electric pump is definitely required as referenced above for all Port Injection systems. A return line is required to the fuel tank. A 3/8 or 5/16inch supply line is required. 3/8 is recommended. 5/16 inch is recommended for the return line. The fuel tank must be vented so as not to buildup pressure. Recommended location for the fuel pump is close to the fuel tank.
Fuel Injectors There are a number of Fuel Injectors on the market today. The following injectors have been furnished on GM OEM systems: Lucas Bosch, Rochestor and Multec. The prices vary considerably and performance differences are hard to detect. Basically they are sized for application. The 5.0L injector is sized to deliver approximately 4.05 milligrams of fuel with a 2.5 millisecond pulse or 18.13 lbs per hr at approximately 36 PSI. The 5.7L injector is sized to deliver approximately 4.83 milligrams of fuel with a 2.5 millisecond pulse or 23.92 lbs per hr at approximately 43.5 PSI. This information is typical for all manufacturers and flowrates will vary slightly even between identicle injectors. A wide variety of flow rates are available to include 19lb/hr, 24lb/hr,30lb/hr, 36 lb/hr. These are all 16.2 Ohms and will work well with all GM TPI's Rochestor injectors are presently furnished for the 90-92 GM 5.7L engine. It has an all metal nozzle and performs well. Bosch injectors an excellent choice at approx $37.00 to$50.00 each. While there are significant differences between the TPI and LT1 induction systems and computers, the injectors are essentially the same. Sequentialport injectors and batch fired injectors are sized in the same manner.
Wiring Harnesses The 1985 Engine Harness for all vehicles incorporates a MAF module which plugs into the harness in the vicinity of the ECM. If you are purchasing a system thru a salvage yard it it always a good idea to just buy the unit and upgrade the electronics to speed density 90-92.It is neater and simple to install and it performs like a 90 to 92. The 1986-89 Harness has three relays and the ESC module mounted in the engine compartment. The 89 harness does not incorporate connectors for the cold start system. Please note that a mass air flow sensors required on all systems thru 1989. Please note that while the connectors for the 85 ECM and the 86-89 ECM are the same, they are NOT interchangeable. The ECM's are different. The 90-92 systems are considerably different than their predecessors. The 90-92 systems use a Manifold Air Pressure (MAP) sensor in lieu of the Mass Air Flow Sensor. This system is referred to as a Speed Density System. The Electric Spark Control (ESC) module is also incorporated in the ECM. All hardware components remain the same ie., intake runners, fuel rails, throttle body, distributor and intake manifold. The EST module, in the distributor and knock sensors are different than the earlier models and must be matched. All hardware components are interchangeable with earlier models. While the 90-92 systems are cheaper to manufacture, it is questionable as to whether Speed density is better than the Mass Air Flow System, especially when GM brought the MAF back in the 94 LT1. But who are we to question GM engineering. All systems appear to perform very well indeed. The 90-94 system has a single relay for the fuel pump mounted in the engine compartment. There is no ESC module as previously discussed. These functions are performed by a module in the ECM/PCM. The ECM's for the 90- 92 Camaro and Pontiac are different than the 90/91 Corvette. The Pontiac and Camaro use a 1227730 ECM and the Corvette uses a 1227727 ECM. The difference between the two is in the ECM enclosure and ECM connectors. The Corvette enclosure is built for mounting in the engine compartment. Camaro/ Pontiac are built for mounting in the passenger compartment. Internally they are the same. Calibrators are interchangeable. It should also be noted that the Assembly Line Diagnostic Link (ALDL) connector IS NOT normally part of the Factory Engine Harness. It is normally part of the instrument panel harness. The factory engine harness also includes a number of connectors which are not required for "Off Road Use". These connectors are Air Management, Transmission, EGR, Electric Fan, Instrument Panel Oil Pressure Sender, Water Temperature sender, AC High Pressure Switch, VSS and VATS module to mention a few. From 94 and up its the PCM and no calibrators. The PCM for the LT1 is the same in the Corvette, Camaro, Firebird, Buick and Caprice. This unit is Programmable as previously discussed. These units are completely different than their predecessors. We can program these units for any LT1/engine transmission combination. Performance and special calibrations are also available.
VORTEC HEADS and TPI Since GM offered the new Vortec cylinder head many customers have ask if a TPI unit would bolt up. At a glance you can see that it will not due to the lack of bolt holes and the wrong bolt angle. A few companies offer a service to put the required holes in the Vortec cylinder heads so TPI will bolt up to these awsome heads.