Cause of Lambda failure?

[huwp]

Sigma 125 engine. Just replaced the second lambda sensor at 12,000 miles. It was very sooted up. Mine is a '07 car and to be honest the mapping has never been great. Could this be why the sensors are failing?

 

Is it worth getting Caterham to update the map (being an early sigma car I presume Caterham would have evolved the mapping software)? That would at least be cheaper than a full rolling road re-map. It also seems no one has the ability to access the ECU other than the two Steves and I'd rather avoid the hassle and expense of travelling to them.

 

Thanks in anticipation.

 

Huw

[DJ.]

Mine has just failed at 20,000 miles on a 2011 car, so I doubt a newer Caterham map would help much.

[huwp]

Makes me wonder whether all that over-fuelling that gives the popping and banging is ultimately damaging the lambda sensor?

[lads ar]

 

 

My 150 Roadsport of 2010 vintage popped, banged and pinked from the off.  The Lambda failed in April 2014, a new one was fitted and then I paid a visit to the Two Steves.  I drove a different car back, it was like chalk and cheese.

[Damo V]

I have had one fail at 4k miles on duratec.

 

do you run a cat? My theory is without the cat it suffers more?

[Smiffy69]

How do you know if its failed? (probably another daft question from me!)

[Damo V]

Mine ran like a pig on light throttle and very rich on idle

[martyn]

A lambda sensor can fail in a couple of ways.  In most instances the sensor will continue to work, but report an incorrect lambda reading to the ECU.  This will cause the ECU to incorrectly adjust the mixture.  As Damo says, it will probably run very rough, use lots of fuel, pop & bang a lot etc.  The problem here is because the ECU doesn't realise there is a problem, you won’t see any error codes or faults if you examine the ECU with diagnostic software.  So you have to look for other clues - e.g. a high or low lambda reading that doesn't ever change much as the engine warms up.

Alternatively (and this happened to me) the lambda can fail internally in some way.  Connector degrading or the wiring breaking down.  When this happens, it is likely that the ECU will detect the wiring fault.  Once the fault is detected, the ECU will ignore the lambda and instead defer to a default map.  In my case (sigma 150) the car ran absolutely fine on the default map and I never knew there was a problem.  That was until I plugged in easimap and saw the error code and that the lambda wasn't oscillating.  The car even passed its MOT in this state!  I replaced the sensor and everything in the ECU went back to normal, but the car felt exactly the same and maybe used marginally less fuel.

I've done a lot of playing about with this and concluded that (for my car at least) the lambda sensor doesn't make much difference.  Either in emissions or how the car feels to drive.  It is narrow-band and oscillates too slowly (about 1.5 hz).  This means that half the time it is slightly too rich, and the other half it is too lean.  The net result there is that on average the fuelling is exactly the same.

 

[DJ.]

When my lambda failed, my Seven accelerated well and idled OK, but became almost undriveable at a steady speed popping and hesitating.

 

 

[Smiffy69]

Thanks Guys - I don't think i have a problem but given it's 5 years old, MOT time and these seem to have a high failure rate I think i'll stick the easymap on mine and just double check.

 

[lads ar]

As above, rough as a rough thing and used three tanks of fuel from Malvern to Lancashire  

[Damo V]

Mine was exactly the same as DJ

[huwp]

Interesting contributions. So is it the mapping that is causing these failures?

 

In 28 years of motoring I've never had one of these sensors fail on another car.

 

Huw

[ChrisC]

I think it could be possition,   They are normally tucked up in the engine bay, and not exposed to all the elements like they are in a seven.    I guess the possition could lead to wire breaks or maybe its the cooling while in operation from wind or water thats killing them.