Can someone fill in the blanks here for me for ECT failure- I'm trying to trace down no fast idle on cold start and a slightly rich mixture, but with good power, driveability.
Scenerio 1:
ECT has a broken wire and so reads 0 volts (means engine hot) so no fast idle on cold start, computer compensates by leaning out mixture, O2 sensor indicates more fuel required so computer compensates by enriching mixture. Where am I too rich or too lean?
Scenerio 2:
ETC has a bad ground and so reads 12? volts (means engine cold) so fast idle on cold start, computer compensates by enriching mixture, O2 sensor indicates less fuel required so computer compensates by leaning out mixture. Where am I too rich or too lean?

Ron
87 745 260000km
near Brantford, On,Can

An open circuit to the the coolant temp sensor will tell the computer that the car is stone cold, you would then get the normal richer mixture and increased idle when engine is actually cold, upon warm up it will run like crap with an over rich mixture.

The sensor actually decreases its resistance as it heats up.

How do you know there is a rich mixture?

Have you checked the idle air motor for proper operation?
--
David Hunter

What's ECT?

FI ECU uses resistance not voltage to determine temp and consequently the related FI.

FAQ gives resitance values to check at the FI ECU input (remove cover and with key off check resistance). If I recall it's pin 3 but don't quote me.

Buy the way, FI ECU temp sensor is shared with the ignition ECU.

I got the nomenclature from the FAQ - the ECT is the temperature sensor used by the FI ECU. I guess I got the units wrong - the sensor reads resistance which is converted to voltage by the ECU. I'm still interested in the relationship between the conflicting enrich/lean out provided by a malfunctioning ECT and a properly functioning O2 sensor. Thanks for the response though.

Ron

The FI ECU compares the resistance value recieved from the ECU Temp sensor to values hardcoded into memory and then provides the appropriate pulses (not static voltage)to the IAC to increase RPM as well as increasing the pulse to the fuel injectors to enrichen the fuel/air mixture.Also note that the ignition ECU adjusts the timing for cold vs hot temperature from the same sensor.
I don't believe that the ECU uses the O2 sensor to very the fuel injection when cold since they are inoperable until they are at temperature.

Hope this will help in your quest for understanding.
Joe