Sensors and Actuators
The complete TPI System relies on data from various sensors (eg Oxygen Sensor) so that engine performance and efficiency is kept at a constant optimum. The system causes actuators (eg Fuel Injectors, IAC Motor etc) to react accordingly. For example, if the Oxygen Sensor, located in the exhaust manifold, senses an incorrect Oxygen level, an electrical signal is sent to the ECM. The ECM prcesses this information and sends a command to the Fuel Injection System to change the air/fuel mixture. This constant activityensures a predetermined, ideal air/fuel ration is maintained, no matter what the conditions.
The following table lists the TPI Systems Sensors and Actuators.
Table 2 - Sensors, Actuators Sensor Actuator Non ECM Devices Exhaust Oxygen Fuel Injector Crankase Vent (PCV) Throttle Position Idle Air Control Motor Engine Temp. Sensor (Overheat Gauge) Coolant Temperature Fuel Pump Relay Oil Pressure Sensor (Gauge) Vehicle Speed Trans. Converter Clutch Oil Pressure Switch (Fuel Pump) Detonation Electronic Spark Control module Cold Start Valve Mass Air Flow Engine Fan Cold Start Thermal Time Switch Manifold Air Temperature Air Control (divert) Solenoid A/C Pressure Cycling Switch A/C Pressure Air Switching (Cat. Conv.) solonoid Fan Override EGR Solonoid Fuel Vapour Canister Solenoid Manual Trans. Overdrive
Corvette and Camaro/Firebird TPI systems also differ in that the fuel line connections exit on different sides of the engine. The Corvette systems lines exit near the front of the right cylinder head and face forward (Figure 5 Page 10), whereas the Camaro/Firebird systems connections exit toward the front of the left cylinder head and face toward the left side of the engine (Figure 6 Page 10).
The Corvettes fuel line position is compatible with accessory mounting combinations which mount the alternator on the left side of the engine. The position of the Camaro/Firebird systems fuel lines work well with combinations which mount the alternator on the front of the right cylinder head, the power steering pump low on the left front corner of the block, the air-conditioning compressor on the left cylinder head and utilize individual V-belt drives for each accessory.
The Corvette system is normally used with a serpentine belt drive. 1988 and later Camaro/Firebird TPI systems also use a serpentine belt drive, but the accessories are positioned differently to the Corvette units.
Also, Corvette engines with aluminium cylinder heads have a unique Exhaust Gas Recirculation (EGR) plumbing arrangement because of the lack of exhaust crossover passages in the aluminium cylinder heads. The lack of these crossover passages require the routing of exhaust gases to the intake manifold via a tube that connects to the right hand exhaust manifold.
The TPI side runners or, as they are more commonly referred to, Ram Tubes, are interchangeable between different years and models, with the understanding that there are specific left and right side units and also, that 89 and later systems are not equipped for a cold start valve. Therefore, the left side ram tube assembly does not have the required mounting provision for the cold start valve assembly, and the 89 and later intake manifolds do not have the proper internal passages to allow the 86-88 cold start system to function properly.
All intake manifolds interchange to any Small Block Chevrolet but, as mentioned, 89 and later manifolds have no provision for a cold start valve assembly. Intake manifolds, used on 87 and later engines with cast iron heads, have the two center intake manifold bolt hold-down holes drilled at a different angle than earlier engines. These manifolds can be used on the early engines if the bolt holes in question are machined, or otherwise opened up, to allow the mounting bolts to be installed.
All of the fasteners used on the TPI system utilize metric threads and most of the bolts used to assemble the individual components of the TPI system use TORX type heads. The intake manifold is held to the cylinder heads with standard 3/8" 16 USS bolts. However, these too have a TORX type head. The intake manifold hold-down bolts require the use of a #T45 TORX driver and the bolts which hold the balance of the TPI system together utilize a #T40 TORX driver. In addition, some of the TPI assembly hardware occasionally utilize bolts with 10mm, 13mm and 15mm size hex heads.
All intake plenum assemblies are interchangeable. Corvettes use an aluminium plenum extension (GM #10108425), which extends over the distributor, that can be used to replace the easily broken, plastic unit used on the Camaro/Firebird systems.
All the throttle body assemblies are interchangeable. However the 89 units use a different attachment point for the throttle cable, which can create additional problems with the throttle linkage hook-up in most non-OEM applications.
If your prior knowledge of TPI systems is limited to some quick looks under the hoods of various Corvettes and Camaros, the names and acronyms of the following parts may seem foreign, and unusual, to you but their functions are really quite familiar. Whether an engine is equipped with a carburetor or fuel injection, it still needs the correct mixture of air and fuel to run. The functions of most of the following components allows them to work together to accomplish this end. For example, a carburetor has a choke mechanism to enrich the fuel mixture when starting a cold engine. Chevrolets TPI uses a 9th injector and an engine temperature sensor to perform the same function. In the following paragraphs, we will attempt to explain the various functions of the major components of the TPI system and, where appropriate, how to accommodate them to a non-OEM application.
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