Air Temperature Sensor And Head Temperature Sensor Test - Mercury 150 EFI Service Manual

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.
a - 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-
ence.
Results: Resistance does not change inversely with temperature change. Replace defective temperature
sensor. Resistance changes inversely with temperature change. Temperature sensor OK.
90-883728 JULY 2001
a
58898
Temperature Sensor Specifications
Fahrenheit
257
248
239
230
221
212
203
194
185
176
167
158
b
b - Head Temperature Sensor
Centigrade
125
120
115
110
105
100
95
90
85
80
75
70
FUEL INJECTION
b
58893
OHMS
340
390
450
517
592
680
787
915
1070
1255
1480
1752
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