Deceleration Fuel Shutoff (engine codes HT, RD, and PL only)
When decelerating, fuel flow to the injectors is shut off to improve fuel economy. At normal operating temperature, fuel flow is shut off when the throttle is closed at engine speeds above 1600 rpm, and fuel flow resumes when rpm drops to below 1300 rpm. Below normal operating temperature, these limits are higher. The closed throttle signal is provided to the control unit by the idle switch mounted underneath the throttle body.
To check the deceleration fuel shutoff function, disconnect the harness connector from the coolant temperature sensor and bridge the connector terminals with a jumper wire as described above under Full-throttle Enrichment. Start the engine and increase engine speed to about 3000 rpm, then release the throttle. The positive differential pressure regulator current should briefly change to a negative value (approximately -45 mA) and then return to its normal positive value.
If the current does not temporarily change to a negative value, check for a faulty or incorrectly adjusted idle switch or a faulty rpm signal from the ignition control unit as described below in Control Unit Inputs.
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