lambda

[urquattro-island]

hello i am getting some mixed info on the lambda probe in 3B. Does it only read air/fuel when idling or also when running?? When running lets say with, exh.leak will it fuel more???

[Rusty]

It measures at part throttle but not at WOT. Not sure about idle either.

[urquattro-island]

ok

thanks mine is blowing black smoke.

[Rusty]

Could be MAF related too. How old is the Lambda? Mine was 12 years old when I replaced it!

[s2driveruk]

Bosch say 60k miles to replace them for optimum use but mine had no record of change until well over 100k miles.. Instant improvement when changed though!

[sheppardnias]

I thought that the lambda probe was used only to control fueling at idle. Once running I understood that the car ran on it's mapping. At idle the mixture is controlled by the probe and hence a faulty probe fails the emisson checks on the MOT, the readout should show emissions of HC's and CO and a lambda value of 1.0 +/- 0.02 iirc.

Once running above idle, I thought that the MAF told the ecu the air intake and that was used along with all other reding to decide which part of the map the engine needed to be fuelled for. This allows the engine to vary its fuel / air ratio depending upon what is needed ie acceleration, deceleration, steady speed.

If the exhaust leaks, it will affect the readings taken from the back due to air ingress and and gas escape where the leak is. The lamda is situated very close to the engine though and I doubt it is affected by the leaks further back. It's just the MOT man who gets upset.

Black smoke suggests over fuelling to me and I'd point a stick at the MAF for a start. See if you can try a quick swap with someone to prove the point.

Hope you get it sorted

Steve

[A80Avant]

i believe that the lamda is in the equation along with the maf when running at any part throttle to have the proper fueling.You can tell this if you have a bad lambda and accelerate in part throttle,that the car is not accelerating smoothly,rather roughly i might say.The same you get if you have a bad MAF as well.

[urquattro-island]

ok

well i ordered new lambda since its never been changed 255 000km and will check the maf,thanks guys..

[sheppardnias]

Would seem that the the Lambda sensor is used under part load circumstances as a closed loop system but when accelerating or under cold start circumstances, open loop control is used allowing the engine to run richer.

All you have to do to avoid problems is drive everywhere on full throttle and only let the car get into traffic when it's still cold....

Who needs a lamda sensor then?

[Rusty]

All you have to do to avoid problems is drive everywhere on full throttle...

[A80Avant]

so what you say is that if you have cold start problems with mixture,it is NOT lambda related?

[Flat on my back]

.

Yes and no, cold start problems can also be related to the coolant temp sensor.

[A80Avant]

right,the white sensor behind the block...