Generally speaking, if a water temp sensor is unplugged while an engine is running, what should happen? A Felicia 1.3 MPi is puzzling me in that there is no difference in running whatsoever, at any temp, if the sensor is plugged in or not. It's a 4-wire job and all that happens when it's unplugged is that the temp gauge stops working. It's had a new one but the results are exactly the same.
Si
With the engine running, generally nothing (with regard to fuelling) The ECU only uses the sensor to calculate the amount of fuel needed for starting. Once the engine is running, and has entered closed loop control (ie. it's relying on the lambda sensor to calculate fueling), the ECU doesn't need to know how hot the engine is to control fuelling.
The ECU may use the temp sensor for other purposes, such as to control the cooling fan, or to detect overheating, but it's not needed for fuelling calculations.
you sure your unplugging the right one ? sounds like its the guage one your unplugging.
Err but doesn't the ECU need to know the temp to ENTER (and remain in) closed loop?
The coolant temp sensor is a primary sensor unlike the lambda which is a trim
4 wire sensors are a VAG thing. Basically two sensors in one package, although you have to make sure you fit the correct coloured one...
That's an open question, it can derive the information to let it run in open loop from other variables.
Only in open loop.
On the crude EFI system on my SD1 it would tell the system to go to maximum rich for cold starting. When it warms up it would stall.
Depends on the ECU, but most modern ECUs will enter into and remain in closed loop mode quite quickly after starting.
Define primary sensor. A modern car will run better without knowing the coolant temp, than what it will without knowing the lambda.
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