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Optional Systems

The following components/systems are not necessarily required for the operation of the TPI. They are included here in cases where emission laws, safety considerations, engineering requirements or personal preference dictates their inclusion.

Air Injection System

If current emission laws require the retention and use of this system, it is merely a matter of leaving it mounted to the motor and attaching the appropriate wiring connectors from the harness to the control valve. You will also have to provide the necessary connection points for the Air Injection Reaction (AIR) tubes to the exhaust system, or obtain a set of Rams Horn type manifolds with the proper threaded holes for the AIR plumbing. These were used on 75 through 81 Corvettes and are available from GM under #372243. If it is desired to remove this system, it also presents no particular problem with the installation as the ECM, while controlling the operation of the AIR systems control valves, does not monitor their operation, and therefore, would be unaware of the deletion of the system.

EGR System

Here again, your states emission laws will come into play. The entire Exhaust Gas Recirculation (EGR) system can be left on the motor to function normally as designed by merely making the proper harness connections and leaving all the components in their factory-installed positions. If it is desired to remove the EGR valve and its attendant electronically-controlled vacuum valve, it can be done, without affecting the electronics or diagnostics of the system, by making the proper connections within the harness.

Park/Nuetral Safety Start Switch

This switch, as its name indicates, is utilised to provide information to the ECM as to whether the transmission is in one of the drive gears or the park/neutral position. It does this by grounding a contact which, in the original GM application, is an integral part of the neutral safety/backup light switch which, when grounded, informs the ECM that the transmission is in park or neutral. As with the EGR system, if the proper connections are made within the harness, this unit can also be deleted.

Vehicle Speed Sensor

The Vehicle Speed Sensor (VSS) sends a pulsing voltage signal to the ECM which the ECM converts to a miles per hour reference. This sensor mainly controls the operation of the automatic transmissions Torque Converter Clutch (TCC) system and also provides an input for the GM electronic cruise control unit. On all Corvettes, and some of the later Camaros and Firebirds, this unit is mounted directly in the transmission extension housing, where the speedometer drive gear sleeve would have been and provides the VSS signal for the above inputs and also for the electronic speedometer. In vehicles that utilised a speedometer cable, the mechanism is a small unit mounted to the back of the instrument panel behind the speedometer and activated by the speedometer cable. In most Street Rod or similar installations this function is not required, unless you would be interested in having the TCC function totally as originally designed, or adapting a late GM electronic cruise control to the installation.

1990 - 1992 TPI engines use a 4-pulse VSS. The 1985 - 1989 uses a 2-pulse VSS

Check Engine/Service Engine Soon Indicator Light

The Check Engine/Service Engine Soon (SES) light is the ECMs method of alerting the driver to a problem in the electronics circuitry of the fuel injection system. In original GM applications, this light is usually contained in the indicator light cluster of the instrument panel. It is also possible to merely add an after-market indicator light, mounted anywhere it is convenient to serve this function. We HIGHLY RECOMMEND the inclusion of this light during your wiring process. Basically,if the ECM disagrees with a particular sensor input, it will turn on the Check Engine/Service Engine Soon light and, at the same time, set and store a trouble code in the ECMs memory, so that you can check the appropriate sensor and circuitry for possible problems.

Just because the light comes on, does not mean there is necessarily a part failure, but only that the ECM is reading inputs outside the normal pre-programmed parameters it expects to see. In a lot of cases, the Check Engine light will extinguish itself during continued operation if there is no serious problem, and, in many cases, will extinguish itself after the engine has been turned off and restarted. In both these cases, however, the ECM will store a trouble code for future diagnostic purposes.

If the light goes on, stays on and does not extinguish itself, especially after a restart, it usually indicates a problem with one of the sensors or the circuitry and should be checked, according to procedures outlined in the GM shop manual covering the SPECIFIC YEAR AND MODEL TPI system that you are using. While this manual is designed to supply you with all the necessary information you will need to properly install and wire the TPI system in your vehicle, without the need for a GM manual, we would be less than candid if we did not tell you the GM shop manuals offer the definitive source of information on diagnosing problems with the TPI system.

The proper year and model manual is especially helpful in troubleshooting problems because of its step-by-step diagnostic charts which are organised in reference to ECM trouble codes. Order forms for the appropriate manuals can usually be obtained from specialty shops. Should you prefer, you can also write for order forms to the Publisher of the manuals: Helm, Inc., P.O. Box 07130, Detroit, Ml 48207. Their information number is 313-883-1430. Helm Inc. also has a toll-free order line for credit card use only (800-782-4356).

Coolant Fan Control Relay

In the original GM installations, all TPI engines utilise an electric cooling fan. This fan is controlled by the ECM in response to temperature input from the Coolant Temperature Sensor and other sources. Unfortunately, in our opinion, G M has seen fit to activate this fan at a much higher temperature level than we like to use. For the most part, we use this circuit merely as a backup circuit for the electric fan, which is also required on most non-OEM TPI installations, because the location of the TPI air inlet ducting precludes the use of an engine driven fan in most installations. We prefer to operate the electric fan either on a full-time basis or wired through an after-market thermostat which turns it on at approximately 200F (93C) and off at approximately 185F (85C), as opposed to the factory turn-on point of from 220-234F (104-112C), depending upon the year and model of the vehicle from which the system originated.

If you are using an electric engine cooling fan in your installation, it should also be wired to run whenever the AC compressor clutch is engaged!

Coolant Fan

We have found that the electric fans, used on 84 and later Corvettes and 85-87 Camaros and Firebirds, are quite adequate for cooling any small block engine equipped with an adequate sized radiator. We recommend mounting this fan in a custom sheet metal shroud to best utilise its air-moving potential. If one of these fans cannot be obtained in a wrecking yard, it can be ordered from GM in 3 pieces as follows: Motor #22074968, Housing #22049527, and Fan #22067444. If this GM fan will not fit your application, because of clearance considerations, there are many different after-market units with more compact dimensions that can be used.

As the preceding information indicates, Chevrolets Tuned Port Electronic Fuel Injection System presents a new perspective for todays performance oriented automotive enthusiast. We hope you have found the foregoing helpful in understanding the system, its terminologies and the areas that require attention, both when obtaining a complete TPI engine or an individual TPI unit, and also when installing it in your Street Rod.

The information contained in the balance of this manual includes specific wiring details, broken down by colour codes, circuit numbers, enumeration of the circuits that must be included, those that may be deleted, and how to delete them without creating false trouble codes. In addition, there are short-cuts and installation hints included that have been utilised during in-shop installations.


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