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The TPI Story

Hilborn Conversions
Programmable ecm

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 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.

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, OBDI 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.

For 96 all Chevrolet engines are Sequential Port and are equipped with On Board Dianostics 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.

Electronic Control Module(ECM)

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

Y=Corvette F=Camaro ,Firebird, Trans-AM
ECMModel      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

Powertrain 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 programed before being placed in service. These Units can be re- programed for any engine / transmission combination.

Model   Year       GMpartNo   Engine
BFY     1994-1995  16188051   5.7L LT1
BFY     1996-1997  16214399   5.7L LT1/LT4

While each of these ECM's/PCM's will provide excellent performancefor 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 are not interchangeable, without modifyingthe wiring harness. The LT1 PCM is not compatible with the earlier ECM's due to significant changes in the distributors of these engines.


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 - 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) 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, in 94 the MAF returned with a 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 1990-94 TPI - LT1 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.

The PCM introduced in the 1994 Corvette, Camaro and Firebirds forthe LT1 engine accomplishes the same functions as the earlier models in much the same way, but there are some significant differences. The 94 and up LT1 is a sequential port fuel injection system. The injectors are fired in coordination with the opening of the intake valve. The distributor and electrical spark timing system, now referred to as "Opti-Spark Control", has an optical sensor which counts light pulses through a perforated disc in the distributor. There is NO timing adjustment for the LT1. The Mass Air flow sensor is back in 94 andi s one of the primary sensors for fuel control. The MAP sensoris a backup for the mass air flow sensor. 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.

The 96 OBDII engines all use EEPROM computers making Chip technology something from the past. These PCM's have the ability to determine a cylinder misfire and will even tell you which cylinder midfired. Opti-Spark is now the standard ignition system on 5.7L LT1-LT4 engines. For 96 a combination crankshaft position sensor and cam shaft position sensor perform the timing functions on all the 4.3L, 5.7L and the 7.4L engines. The LS1 is now the new small block appearing in the Corvette in 97 and the Camaro / Firebird in 98.


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.


All 85-86 systems used a GM HEI distributor. The connector for the distributor is keyed differently than previous model years. 87-92Camaro and +Pontiac 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.

As mentioned earlier the LT1/LT4 has an optical sensor and is significantly different than the HEI system. Distributors are not interchangeable for these different engines.

Fuel Pumps

The OEM fuel pump for TPI/LT1 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. We also offer a chassis mounted fuelpump which has an operating rating of 60 PSI and 30 GPH. This pump is also an AC DELCO unit. 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.

Painless or Painfull, try our Harness

Here we will compare Apples for,Apples or will we?. A Painless harness is Not finished, Not wrapped, Not loomed and Not soldered and start at around $295. Our Custom harnesses are fully soldered(every connection) and wrapped in GM ,gray stripe loom, and then dry vinyl wrapped for $295 for the basic TPI Speed D harness. PAINLESS prom is $195 and still has VATS in it!Then for another $50 they will wipe vats with a high failure rate external device that can leave you stranded. Our Proms are VATS FREE for $149 as well as early Fan ON, No egr if requested No VSS if requested,and we also offer a 4 k square wave input for a single drac speed signal to be inputted when needed.ALSO, since we install what we make we offer tech support and are familiar with the problems you encounter and can diagnose and take care of problems over the phone if needed unlike some companies that do not even understand what they are selling.Do the research, ask all the questions, and decide for yourself.A product will sell itself every time.Also we finalize each order based on your needs like: HEI dist or small dist with remote coil, 1 wire or 3 wire heated O2, air temp sensor type and location, 4x4 or 4x2 so vss wiring will reach a transfer case or not.This is done so you do not have to have a one fits all"universal" harness with some circuits too long or connectors that do not mate to your equipment.We also convert harnesses if you are a Throttle body truck or Camaro and want the totally factory looking harness when the job is done rather than adding in another harness.

Special Application Harnesses

We have custom TPI harness for specific applications like C3 Vettes and 81 and up G body cars. Our G harness is made to replace an exsisting feedback carb harness and enter car through factory hole near pass door hinge as well as plug in to the 15 way IP(instrument panel)plug found under pass side dash.The G harness lays on RH inner fender and feeds the TPI from pass front just like the factory carb harness did.It positions a MAP plug and fuel pump relay on the RH inner fender well.It allows the use of the factory ALDL and Service light and has provisions for egr, can purge and diverter valves as well as 700/200 control. Our C3 Vette harness is a harness designed for a easy installation and No need to pass thru fire wall other than for service light, and brake signal(if 700) . It uses a 1227727 (90-91 ) Vette ecm which mounts to LH frame just under steering .