checking lambda sensor

[Seight-v8]

so been down for an MOT test at my local garage today....and failed on idle & fast idle readings.....

I have 1.00 set in my table at the 750rpm & 2500rpm areas....but car is still reading high....

Is my sensor reading incorrectly....as i've got to presume the garages readings are right....

Any other way to test my lambda sensors readings.....

cheers

scott

[rob@vems.co.uk]

Just on O2 or on other gasses too?

[Seight-v8]

well here's the story....

Went for MOT...and when we came to emissions the readings on the MOT tester where rich and it failed.

So i changed the target lambda around 2500rpm to 1.04 lambda and re did the test....my lcd shows 1.04 lambda at 2500rpm....yet the MOT tester is showing 0.94-0.95 lambda...so still rich....

Now i am lost.....i am thinking my lambda probe is not telling me the correct mixture anymore....and how can i test it.

I did the free to air calibration over 18 months ago, but can i test it again after this much use.

I need to know if my readings are corrent before i try for a retest., otherwise i might be wasting my time

cheers

scott

[rob@vems.co.uk]

Mmmm, it sounds like the calibration is off - but you cannot reasonably expect to get a decent free air calibration from a used sensor.

You might benefit from pulling the sensor from the exhaust, turn the heater on, and leaving it to burn off any soot and contamination.
I've been lucky enough to find people with 6gas testers that allow me to mess around.  Knowing Lambda is only part of the story, it would be handy to know your HC and CO to make sure that your injectors are indexed with the engine correctly, strange things can happen with part burned charges.

[Seight-v8]

cheers rob,

I am away from home all this week, so cant do anything on my car, got and issue with my MOT tester checking the emissions when looks like i only need a visual check, so this should sort one problem.

But i am now worried that my lambda readings aren't good, i did pull the sensor late last night and it was very black/sooty on the outside......

I did check the free to air calibration again and it was the same (178) when the sensor was unused......so left the settings the same.....maybe it just needs to burn the soot off.

Will do more this next weekend when i am back.

cheers

scott

[rob@vems.co.uk]

Trouble is that if you're setting up fuelling, breaking in a new engine or any number of things where the engine never sees any load, then you're sitting at the lowest VE of the engine with relatively low exhaust gas temperatures and speeds.  A good hard 15 minute blast may change the state of the sensor's soot contamination.  My MOT station always insisted that cars come to them after at least 10mins normal running, so the engine would be as clean as it could be.

[Seight-v8]

cheers rob, i have fitted a new plenum over the winter and a new set of injectors just last week before the mot test....i knew the table needed some work, as i recon that the plenum alone had altered the fuel table by up to -20% across the table....

i proberly had not driven it enough to get the table to as near as it should have been......again i am still learning about my vems....

i need to drive it to get the fuel table better....and i needed an mot to do this.....

hopefully if i can get it moted when i cant get back and i can do some proper road tuning/logging and get some road miles to get it bedded in better....only did 400miles last year on rebuilt engine.

ultimately i wanted 1k miles on it before subjecting it to any rolling road tuning, and i think this is my best option to get the car running right, as i just dont have the knowledge to do so myself.

scott

[boostd audi]

ultimately i wanted 1k miles on it before subjecting it to any rolling road tuning, and i think this is my best option to get the car running right, as i just dont have the knowledge to do so myself.

i dont understand why you are waiting to map your VE.  breaking in a motor with a config that is untuned is not a wise decision..

to b break in a motor just KEEP TIMING LOW, and map your VE..  then do your 1k miles..  then add some timing back in when you feel the motor is ready and broken in. but driving around on untuned VE table is not helping you.

[rob@vems.co.uk]

Catch 22,  you need the car mapped - well. To pass an MOT.  But an MOT to map the car.
Trouble is that road tunes are not always particularly good (inability to hold a steady state or get repeatable transients), and you're likely to get a chance to explain yourself to a court of law if the Police take exception to you mapping on the road (which they do).

What you need is either a private runway or a rolling road.  A mate of mine is taking his car to Bruntingthorpe for something like 180quid for the day.

[mattias]

to b break in a motor just KEEP TIMING LOW, and map your VE..  then do your 1k miles..  then add some timing back in when you feel the motor is ready and broken in. but driving around on untuned VE table is not helping you.

This.