Emissions and Lambda

[ButtonIt]

Forgive all the questions, PH search is sh... ocking.

MOT has failed on emissions (should be 0.5 but it's reading 5.9 or something) and the garage have said the Lambda sensors aren't cycling as they should.

Anything I can test,or will I have to stump up for two new Lambda sensors?

Thanks guys, I'm almost there now!!

[blitzracing]

You needs some decent diagnostics- probes are expensive to replace if they are not faulty. The fact they are not cycling could be due to an over rich or lean mixture.

There is the Steve Heath ECU mate:

http://www.ecumate.com/

or Rover Gauge.

http://www.pistonheads.co.uk/gassing/topic.asp?h=0...

(Jump to page 8 you want some pictures of its readings)

Edited by blitzracing on Thursday 8th November 20:45

[ButtonIt]

I disconnected the ECU and gave the battery a good charge overnight. Started this mornign and on idle it starts OK, then as it warms up it begins to hunt and eventually just stops. This is sounding expensive...

[Pupp]

ButtonIt said:

I disconnected the ECU and gave the battery a good charge overnight. Started this mornign and on idle it starts OK, then as it warms up it begins to hunt and eventually just stops. This is sounding expensive...

Worth trying a new coolant temperature sender... they cause all sorts of mixture related issues when they fail/go out of spec and are not expensive (the ECU facing one, not the one feeding the gauge)

[blitzracing]

ButtonIt said:

I disconnected the ECU and gave the battery a good charge overnight. Started this mornign and on idle it starts OK, then as it warms up it begins to hunt and eventually just stops. This is sounding expensive...

Its only expensive if you simply throw parts at it to try and fix it- although I agree a temp sensor is nice and cheap and easy to change- an open circuit or high resistance one will cause it to over fuel and the probes will stop switching. Another common one is the AFM either fails, or the connections to the AFM fail, both cause chronic over fueling. Mind you it could be a lean mixture if it hunts and dies. This could be a big air leak in the plenum area or pipe somewhere- It depends what the probes have been doing- if they are stuck at 0 volts its over lean- if they are stuck a 1 volt or more its over rich. They require different diaganostic techniques. There some good info here:

http://www.g33.co.uk/images/PDFS/14cux%20faulot%20...

[ButtonIt]

Thanks guys, would this relate to the emissions at all? Would a lean mix make the emissions more?

[blitzracing]

Yes- lean means the mixture does not fully burn effectively so one type of pollutant goes up (NOx) and rich means the excess un-burnt fuel appears as Hydrocarbons and the Carbon Monoxide values shoot up due to lack of oxygen in the burn. If you have the gas report from the MOT it will tell you whats going on. The readings you quote could be a C0 (Carbon Monoxide) value, and a value of 5% is running too rich. This chart shows you all the pollutants- your car should run in the green band, but with 5% CO ( read in % from the scale on the right) it will be off in the red end to the left.

Edited by blitzracing on Friday 9th November 14:44

[ButtonIt]

Hmm it turns out that the relay that controls the fuel pump also controls the Lambda sensor heaters. The cheapo relay I fitted was cutting out the lambda heater sensors when the fuel pump was activated.