Lambda sensor advice. X teg v70

[D5meister]

Not sure how a gragh of it would look, so couldnt say for certain.

I will take a look in bosh engineering handbook.

Hmm if working, the gragh jumps about in the endless search for the correct mixture.

With flatline either there is generous airleak in exhaust , but u would hear that..


Probably just dead senso
If you know u have leak can you do a temporary patch repair,, if the sensor then reads correctly then fix the exhaust.

If u bang a new sensor in and still flat, its the exhaust leaking

[Chris_Rogers]

You may find that the front lambda sensor won't produce a response on OBDII diagnostics as it's a wideband type.

I'd suggest you fix the exhaust leak first.

[KBB]

Wide band O2 sensors do not switch rich/lean like titanium or zirconia sensors. The best test for them to see if they react to excess air and rich fuel is to use a forced test method. With the scan tool running in live data with both STFT and O2 sensor remove the hose from the brake servo to create an air leak and look for a reaction on the graph the STFT should go into positive number if the sensor sees lean. To simulate a rich condition introduce LPG (plumbers torch) into the intake and again look at the graph and the STFT should go into negative numbers proving sensor reaction.

[Bigneil]

Thanks for all the great information guys.
Payday on Friday, I'll get the suspected leak looked at straight away as my first port of call, then if necessary move onto the sensor.
Logically, dealing with each in that order will either fix the issue or rule them out. Either way I will be happy that progress is being made.

[oragex]

Just a side note, when the front sensor goes bad, usually it affects city mileage because the sensor works mostly on acceleration. If city mpg is looking good, say around 23 the sensor might be working properly.

[KBB]

Vacuum leaks normally present them selves at idle. With scan tool in live data note the STFT at idle. With a leak present the STFT will go into positive numbers to counteract the lean condition. Raise engine speed to 2500rpm and hold, if the STFT was in positive territory under load the STFT will go negative this is because manifold pressure at idle is in negative pressure and under load moves toward atmospheric pressure where an air leak has little effect.

[Bigneil]

Originally Posted by KBB

Vacuum leaks normally present them selves at idle. With scan tool in live data note the STFT at idle. With a leak present the STFT will go into positive numbers to counteract the lean condition. Raise engine speed to 2500rpm and hold, if the STFT was in positive territory under load the STFT will go negative this is because manifold pressure at idle is in negative pressure and under load moves toward atmospheric pressure where an air leak has little effect.

Thanks for sharing your wisdom, much appreciated. However, I have no idea what an STFT is?

[4candles]

Short Term Fuel Trim,,,

[Bigneil]

I have some extra information: car runs rough when cold, rough idle and jumpy kangaroo when driving off.

I put it down as an innocent quirk of an old and high mileage engine (179000) and was content to give it 10 minutes to warm up before driving off because it runs nice when it has started to warm up a bit.

It occurred to me that this could be a dicky coolant temp' sensor issue...which in turn could cause a knock on effect on other systems such as fuel/air ratio or ignition timing.

[4candles]

Originally Posted by Bigneil

I have some extra information: car runs rough when cold, rough idle and jumpy kangaroo when driving off.

I put it down as an innocent quirk of an old and high mileage engine (179000) and was content to give it 10 minutes to warm up before driving off because it runs nice when it has started to warm up a bit.

It occurred to me that this could be a dicky coolant temp' sensor issue...which in turn could cause a knock on effect on other systems such as fuel/air ratio or ignition timing.

My V70 failed its Mot recently on emissions, very high emissions and i too thought the coolant sensor may be the culprit, but i have no time presently to look into it so i have SORN'd it and bought the XC. V70 was also a bit lumpy and jerky when cold, and also had extreme difficulty starting it on one occassion whereby it also took forever to settle down?
My reader declared the Lambda is at fault but i am of the opinion it is merely tainted by the over-fuelling...Hopefully i may get a chance to look into this before 2016!