Am I right in thinking that the JECS ECU controls fuel mixture via the lambda sensor?

I assume that ECU reads the air/fuel ratio from the lambda sensor, and learns over a period of time whether the engine is running rich or lean, and then adjusts the fueling appropriately. Is this correct?

The reason I ask, is that I beleive that the misfire in my car maybe due to a faulty lambda sensor.

When started from cold the car misfires, and is accompanied by a smell of petrol, I beleive this to be caused because the engine is being flooded with fuel. The reason it starts fine from warm, is due to the heat from the engine assisting in the ignition of the 'over-rich' air/fuel mixture.

The car also pops and bangs a lot on the overun once warmed up, even though both CATS are still in place. I have also noticed that the tailpipe of the exhaust is coated heavily in black sut. Once again, this implies the car is running rich.

I can't think of any other reason why the car would run rich, apart from a faulty lambda sensor.

I have reset the ECU by connecting the two wires under the dash, as I understand this should force the ECU to check all the sensors... everything was fine.

When a lambda sensor fails, does it fail all at once, and stop working, or does it fail over a period of time, giving incorrect results? What is the best way of testing the mixture / lambda sensor?

Anyone have any ideas?

Thanks

SimonM


[This message has been edited by SimonM (edited 05 December 2000).]

 

What about the coolant temperature sensor ?

This acts on the water temperature and adds additional fuel in gradually smaller quantities as the car warms up (as I understand it). When the car is fully warmed up, it stops the "topping up" process.

Probably worth checking....

Thanks

Gavin

[This message has been edited by GavinP (edited 05 December 2000).]

 

Simon

There are a number of things which the ECU reads to determine fuelling. Lambda, engine water temp, intake air flow and atmospheric pressure are the main ones. Readings from the knock sensor are another.

I strongly suggest that you get your dealer to use a Select Monitor on the car. He will be able to read the output from all of the above. This will show up up erratic/erroneous readings on a sensor which has not yet completely failed.