Technical overfueling/running rich???

[Steely]

right the stilos doing silly things at the moment, one being stupid fuel economy, and bogging down whni i accelerate,

if i accelerate from a standing start as soon as it hits 3 k it hesitates and splutters then picks up again,

its obvious its runnign rich as the exhaust is coked up, and its getting about 20 MPG at its best,

the obd is throwing the lambda pre cat sensor odd times too,

anyone got any ideas?? its had new plugs and coils about 2 months back?

what would cause it to over fuel? its not runnig cold or overeheating, just running rich,

 

[PNL]

Mmmmm pre cat lambda ..you checked it..

 

[Steely]

well its a new ona a few weeks back, but surely yhat wont cause it to overfuel? i thought it was there purely for emmissions and cat relative?

 

[PNL]

Read what is says here about lambda/oxygen sensors..

http://www.aa1car.com/library/1999/cm69910.htm

All ecu and sensor related no doubt..

 

[Deckchair5]

Your pre cat O2 sensor is vital for accurate fuelling and smooth running. It tells the ecu how to trim the fuel when the engine is at steady rpm i.e tickover and also when at a steady speed which is quite a lot of your drive (it's ignored when accelerating). Without it, your car will drink the fuel


I'd check the O2 sensor for two things at the O2 connector
heater wires-
both the same colour-usually white or grey- -engine off- check for low resistance of less than 20 ohms as it's a plain and simple heater. High resistance means it's broken, the most common failure of O2 sensors


Lambda sensing itself. (shown testing here on a Bravo)
Look in the Stilo guides on electrical component testing and test the lambda voltage output by back probing the connector on warm tickover (the other two wires -often black and red- and you're testing voltage -not resistance this time). It should oscillate between around 0.15v and 0.8v every few seconds
WARNING watch the leads if you're near the rad fan as it may switch on suddenly


Easier as shown with a set of test leads like these, available at Maplins


If the sensor is bad and you replace it then don't forget to reset the ecu afterwards as long term fuel trims will be wildly wrong