the sensor is going high Z momentarily - Saab 9000 Bulletin Board - Saabnet.com
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the sensor is going high Z momentarily
Posted by Ken Fisher [Email] (more from Ken Fisher) on Thu, 19 Apr 2012 19:28:18
In Reply to: Why replace NTC coolant temp sensor?, Bill Homer [Profile/Gallery]
, Thu, 19 Apr 2012 10:43:33
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The NTC temp sensor (negative temperature coefficient) is the input that moves the ECU program out of 'coldstart' state into 'normal run' state. In coldstart, the idle timing is fixed at 10 degrees BTDC and the pulse width to the injectors is wider to effect a rich mixture. When the engine is first started from cold, the ECU will open the IAC to achieve a high idle, most often 1300-1500 rpm, then adjust the IAC aperture after reading the DIC ionization data. When the coolant sensor reaches 65 maybe 70 degrees C, the idle timing is no longer static, and the pulses to the injectors narrow.
The NTC coolant sensor resembles a thermocouple; a twisted pair junction of dissimilar metals. I think that it is going high impedance and pushing the ECU back into coldstart state. As the engine temperature increases, the junction appears to be intact and its impedance drops into a normal range.
Last time I looked, eeuro sold that part for $14. RockAuto has one from Airtex for $12.
posted by 67.188.19...
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