Service manual

90-898303 2-15

THROTTLE POSITION SENSOR (TPI)

The TPI transmits information to the ECM during low speed and mid range

operation, related to throttle angle under various load conditions. TPI

adjustment is a critical step in engine set up (Section 2C). Disconnecting the

TPI will increase fuel flow 40% at idle but does not effect WOT.

NOTE: The higher the resistance the richer the fuel flow. Refer to TPI

Adjustment.

Other Components Associated With ECM

12 VOLT BATTERY

The 12 volt battery provides power to the ECM even with the ignition switch in

the “OFF” position.

IMPORTANT: When disassembling EFI System DISCONNECT BATTERY

CABLES.

STARTER SOLENOID / KEY SWITCH

Provides 12 volt signal when key is in the “start” position. In the “start”

position, injector pulse widths are tripled when engine head temperature is

below 90° F (32.2° C) to provide adequate fuel for quick start up. When key is

returned to the run position or engine head temperature is above 90° F (32.2°

C), pulse widths return to normal value.

FUEL INJECTORS

A four wire harness connects the fuel injectors to the ECM. The red wire is at

12 volts and connects to all injectors. The blue, yellow and white wires each

go to a pair of injectors and are normally at 12 volts for a zero differential. To

fire the injectors this voltage is brought down to near ground creating a

potential across the injectors.

Notes

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