Confusion regarding Emissions

Spud5467

My car failed the NCT twice on the emissions (toyota Corolla 1994)

Exhaust Emissions:

Engine/oil temperature - 87c

Low Idle (820rpm) - CO 0.39% vol% (PASS) - HC 391 ppm (NA)

High Idle (2980rpm) - Lambda 1.10 (FAIL) - CO 0.68 vol% (FAIL) - HC 240ppm (FAIL)

I have taken the car to two places and have pretty much just told me different things so I don't no what to think.

One place said manifold was leaking therefore pulling in air and sensors needed further analysis. Other place said hole in the exhaust, cat would properly need doing and because she is burning oil would have to rehaul the engine.

The oil goes down but quite slowly I'd say. No blue smoke so maybe its just a oil leak?

Be great if someone could suggest something because its really annoying me. Car drives 100% and has little miles on in (if the odometer if to be believed). I have no reason to suspect otherwise as I have driven the same car with more miles and it drove considerably worse.

Plug

First of all get the holes in the manifold sorted first then get some results and see whats left. The HC's seem quite high so you may need a cat. Lambda is wrong so it could be a dirty airfilter, faulty 02 sensor or airflow sensor.

crosshair1

If you have an exhaust leak(air entrained) at or before the lambda sensor (ie manifold), this will cause the lean lambda value that you have at the tailpipe and cause the ecu to increase fuelling causing elevated hc and co.
You may still need a cat after this is corrected.
Oil consumption will not be an issue unless your adding more than something like a litre every 500mls.

crosshair1

crosshair1 wrote: »

If you have an exhaust leak(air entrained) at or before the lambda sensor (ie manifold), this will cause the lean lambda value that you have at the tailpipe and cause the ecu to increase fuelling causing elevated hc and co.

That makes it sound like the "lambda sensor" is an actual physical thing....I always thought the lambda value was just a way of assesing co2 and hc emmissions on some sort of a curve??
Maybe I am totally wrong and have been neglecting to change my lambda sensor all this time....

crosshair1

The "lambda" sensor (technically its an oxygen sensor) generates a voltage proportional to the quantity of o2 in the exhaust.

Lambda itself is a ratio equation of air mass to fuel mass that is 1 at ideal combustion conditions, ie 14.7 air to 1 fuel.
It can also be calculated from the exhaust gas quantities of o2, co2, co and hc, this is what a gas analyser does.
If your car is from 2001 onwards it is reasonably well able to self diagnose a fault o2(lambda) sensor and most faults would result in and EML.