my passenger side O2 sensor had packed up (according to the Techtom) and the evidence was supported by running rich on that bank of cylinders. Got it replaced and that doesn't seem to have fixed it. It seems to work whilst the engine is cold-ish, but then fails lean (hence the rich running) when it warms up. Symtoms are identical with both the old and the new. I have definitely replaced the correct one (LOL) and connecting up the old one outside the engine I have verified that the heater at least works. so the connection or part of it is good. As I also get sensible-ish readings when cold then I assume the rest of the wiring is good too (the plugs are not full of green fungus).

 

So, I need inspiration, what to look for next ? Only thing I can think of is checking continuity between the harness and the ECU, but that would appear to be good, given that I get some readings. Unless of course I got a brand new faulty sensor !!!!!!

 

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As it seems that the two sensors are very similar (if not identical), could you just swap them over and see if the problem moves to the other side?

Yep Spot on Dave,Andy if that dont work it could be a dodgy injector .

 

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Question Andy, does the actual 02 sensor actually go lean when warm or does the ecu interperate the signal as lean when in fact it has not,could it be another associated circuit fault (not the wiring) or possibly a malfunctioning ecu.

I think it unlikely you have a faulty new sensor and as the fault is identical I do believe you need to rethink the search, having had to fix all kinds of electrical / electronic type faults (not cars) in my work often the fault hides itself or can be disguised by an adjacent piece of hardware that gives the same problems.I find that in these situations you some times have to look outside the area that is giving the fault, hope this make sense, see my service engineer background coming out then. Good luck mate.

 

Jeff TT

Jeff is correct - just because the O2 sensor is giving a different reading doesn't mean the sensor is faulty - the engine could actually be running under the conditions the O2 says it is!!! I'd say you have a fuelling problem on your left bank - like ian says probably the injector connector...

 

Hope this helps...

 

CheerZ,

 

Andy

Been racking my brains over this and still don't know what to do. The O2 sensor when warms up consistently reports lean, i.e. below 0.5v. However, looking at the exhaust the car appears to be running rich. Therefore, I am beginning to think that I could have a problem with one injector, perhaps running lean, which leads to the O2 sensor reporting lean, the ECU compensates by over fuelling on the other two cylinders. BUT, how come with two cylinders running rich the O2 sensor still reports lean (Riddle me this, riddle me that!) ? And why does it only do it when warm ?

 

Good suggestion though, easy stuff first - I will double check the injector connections tonight.

I suggest you use a 4 gas anyliser to check the o2/co2/hc/co reading are factual so you know what the exact fueling you are having , this would tell if you correct lambda for optimum AFR which is 14.7 to 1. the colour of the exhaust is not an ideal reading for telling if its runing rich unless you have done a 70 odd mile down the motorway.

juts my two penny's worth

That will have to be my next step. I'll also be at SE on Thursday, so we'll see whether they have any inspiration. (Of course it could be a duff O2 sensor!)

A quick sanity check here gents - do you have an exhaust leak prior or near to the the Hego? (It doesn't have to be very near, or very big, from experience by the way - the hego is extremely sensitive) If you did the heat expansion would open the leak which would bleed in oxegen rich air, the management would see it and richen up that bank accordingly...

 

just a thought.

To further deepen the mystery, according to the Techtom that bank of injectors tend to show a fractionally smaller opening time .... Now I'm really bloody confused - might try changing ECU maps !

 

Can the ECU really run each bank of cylinders differently ? Seems bloody unlikely, unless something is causing it to read a different part of the map ????

Would you adam and eve it, the things started working correctly now !!!!! Do O2 sensors need running in ? - they live in a pretty hostile environment. So approx 200 miles after changing the sensor and it seems to have got better - hurrah ! (something else has broken to compensate though - more later)