o2 sensors rich/lean

xr8AU2 · 28-12-2007, 02:33 PM

just put my ute into ford for a diagnostic on the problems im having with it....they have come back and told me that one of the o2 sensors is running very rich and the other is very lean, they did a compression test apparently and came back good.
but still cant find out what is causing the problem for the sensors to be like this.
Has anyone had this problem before that could maybe throw me a hint to whats causing this.
just replaced both o2 sensors
injectors
leads
ecu

ratter · 28-12-2007, 02:49 PM

All being well the O2's should be cycling rich and lean continuously. Did you use genuine sensors when you replaced them or cheapy ones?

xr8AU2 · 28-12-2007, 03:05 PM

purchased the bosh from repco.
apparently there supposed to only cycle between 1% rich /lean but 1 of mine are continuously rich and the other continuously lean ....why it running like a pig.

GOF · 28-12-2007, 03:28 PM

The fumes given off by silastic going through the motor can poison the coating on a EGO sensor and cause it to be very slow to read or even give up completly as can a coating of carbon from a dribbling injector or shot oil rings. Finally you can destroy the sensor by trying to measure it's resistance with a multi-meter. Jaycar have a kit which gives a LED bar graph readout of the voltage output from the sensor which can be left connected permanently which allows you to judge the health of the fuel system. When you floor it it should instantly go dead rich, back off, dead lean and crusing contantly flickering around the mid range. From memory the EGO output is zero voltage when cold (it needs to run at about 350 deg C) or rich and a miniscule voltage when lean. Perhaps the one reading rich is RS and fooling the ECU to run excessivly lean and the other one is telling the truth.