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

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 an 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 interchangeable 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 Air Pressure 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 for the 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 and is one of the primary sensors for fuel control. The MAP sensor is 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 and VCM's have the ability to determine a cylinder misfire and will even tell you which cylinder misfired. 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, 5.0L 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 LS1 does not have a distributor. The PCM uses the information from the crank and camshaft position sensors to calculate timing and fires the individual ignition coils.

One thing is CLEAR, Innovation is alive at GM.


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 drilling 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.

LT1 Throttlebodies

The 93 Throttlebody on the LT1 engine is similar to the TPI, but does not have an EGR port. The throttle linkage lever is also slightly different. The 93 throttlebody does have a stud for the trans TVS cable. The 94 and up units do not. If you are using a 700R4 / Turbo 350 transmission, a stud will have to be mounted for the TVS cable.


Stamped - F=Camaro, Pontiac Y=Corvette

TPI Fuel Rails

The TPI 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.

LT1 / LT4 Fuel Rails

The 93 Fuel rails do not have a crossover tube at the front of the intake, nor does the intake have provisions for the crossover. The crossover setup is on all 94-97 LT1 engines. The fuel supply and return lines are on the left side of Camaro, Caprice, Cadillac and Buick engines. The Corvette has both the fuel lines on the right hand side.

LS1 Fuel Rails

The 97 LS1 has provisions for a supply and return line. The 98 and up fuel rails have a supply line only. The fuel system of the 98 LS1 has a regulator built in to the fuel pump return assembly the return line is from a "T" fitting between the fuel filter and the engine.

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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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