Nct-Lambda reading

MAYOMICK

I have a 1997 Toyota Starlet with 130000 miles and it will be going for nct shortly.The Lambda reading for the last four tests were as follows:
2012 1.00
2013 1.02
2014 1.02
2015 1.03 (Anything above this is a FAIL)

What can I do before the test to bring down reading.There does not appear to be any leak in the exhaust system.

CiniO

Do nothing. Most likely it will be OK.
Lambda reading is not something that would degrade with time.

mickdw

CiniO wrote: »

Do nothing. Most likely it will be OK.
Lambda reading is not something that would degrade with time.

Well the old results suggest that it is drifting to dangerous territory over time

blackbox

A high lambda reading implies there is surplus oxygen in the exhaust. Perhaps you have a small leak where air is getting in that is slowly getting worse.

Alternatively your lambda probe(s) may be gradually failing. They don't last forever.

In either case, there is probably not much point in taking action until it fails. (unless you have an exhaust leak that could allow fumes into the cabin!)

nd

Here's some interesting reading on lambda

http://www.austincc.edu/wkibbe/lambda.htm

It's seems your fuel mixture is getting a bit leaner than it should be, every year.

You could try cleaning your air flow meter.

*is a slow typer* Didn't see blackbox's reply before this post.

MAYOMICK

Thanks for replies.I'll get under it at the weekend and check it out thoroughly.

Ded_Zebra

blackbox wrote: »

A high lambda reading implies there is surplus oxygen in the exhaust. Perhaps you have a small leak where air is getting in that is slowly getting worse.

Alternatively your lambda probe(s) may be gradually failing. They don't last forever.

In either case, there is probably not much point in taking action until it fails. (unless you have an exhaust leak that could allow fumes into the cabin!)

Well if it is caused by bad probes causing a leaner than ideal running condition then performance will be effected as well as economy.

Personally I would investigate further into the cause.

Don't forget that the problem can also be at inlet side of things. Unmetered air can leak for example via bad inlet manifold gasket or a degraded pcv hose.

MAYOMICK

I checked the exhaust by blocking it with a rag and the is definitely no leak.The air filter hasnt been changed in a while,Would that make any difference.

jimgoose

MAYOMICK wrote: »

I checked the exhaust by blocking it with a rag and the is definitely no leak.The air filter hasnt been changed in a while,Would that make any difference.

A dirty/partially clogged air-filter would probably cause a low lambda, that is to say a rich mixture condition. The others have pretty much covered the scenario earlier in the thread - it is more than likely something quite simple. How are the other readings doing, that is CO and HC?

jimgoose

Ded_Zebra wrote: »

Well if it is caused by bad probes causing a leaner than ideal running condition then performance will be effected as well as economy...

Exactly. This kind of lean condition is a classic cause of a misfire.

MAYOMICK

jimgoose wrote: »

A dirty/partially clogged air-filter would probably cause a low lambda, that is to say a rich mixture condition. The others have pretty much covered the scenario earlier in the thread - it is more than likely something quite simple. How are the other readings doing, that is CO and HC?

In last Test Jan 2015 CO 0.02 vol%
HC 32 ppm

nd

Here's a good video on finding vacuum leaks

MAYOMICK

I changed the air filter and threw a shot of Lucas fuel treatment in the tank.It passed with the following readings
Lambda 1.00
CO 0.16%
HC 72ppm