Air Temperature Sensor And Head Temperature Sensor Test - Mercury 225 EFI Service Manual

3.0 litre work, electronic fuel injection

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Air Temperature Sensor and Head Temperature Sensor Test

Purpose: This test eliminates possibilities of improper fuel delivery related to air/head temperature sensors.

NOTE: Air/Head Temperature Sensor functioning can be monitored using the Digital Diag-

nostic Terminal (DDT). The Air Temperature sensor should indicate ambient air tempera-

ture. The Head Temperature sensor should indicate cylinder head water temperature. The

ECM will revert to a default temperature of 32 F (0 C) if it should lose either air or head

temperature sensor signal. The sensors can also be tested using a DMT2000 Digital Multi-

meter 91-854009A1.

Air Temperature Sensor

Disconnect temperature sensor harness and check continuity with digital or analog ohm-

meter test leads between both connector pins. With engine at temperature (F ) indicated,

ohm readings should be as indicated 10%. There should be no continuity between each

connector pin and ground.

1. Disconnect and remove temperature sensors from engine.

2. Connect DMT (91-854009A1) to leads of sensor.

3. Place sensor in ice water while monitoring meter reading. Use chart (below) for refer-

Results: Resistance does not change inversely with temperature change. Replace defective temperature

sensor. Resistance changes inversely with temperature change. Temperature sensor OK.

OCTOBER 2001

Temperature Sensor Specifications

Head Temperature Sensor

FUEL INJECTION

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