G40 Failed MOT emissions test

[stuG40]

G40 failed on Mot emissions test on Saturday, car is running very rich.

I previously set the co pot at 550 ohms using a multimeter but emissions still way of the chart.

I connected to the digifant using the snap on solus machine via the k line in the car, and was getting a reading of -17 degrees at idle.

question is, is it worth spending 150 euros on an after market co pot before i put the car on a gas analyser?

thanks

[Andy]

Which part of the emissions test did it fail? Has it got a catalyst on it?

If it's rich (i.e. it failed on lambda reading), then you need to investigate why it's not going into closed-loop lambda control - could be the probe, could be a plethora of other things.

[stuG40]

Thanks for the reply Andy,

I will post the emissions stats later,

the car has recently been turbo converted, so there is no cat (although went through every year without) as for the lambda probe i checked it and seems to be working fine,

However, a single BLACK wire from the lambda back to the ECU has been snipped by someone in the past (intentionally )  , but I when i checked autodata the black wire was for the lambda pre heater, do you think that would effect fuelling?

I was more concerned that the co pot was reading -17 degrees. ps all sensors, leads, plugs ect are all new.

[hayesey]

inlet air temp always gives crazy readings on diagnostics things I've found, such as VAGCOM, usually reads something like -20deg.  I just don't think they are converting the reading correctly for polo digifant.  so I wouldn't worry about that.

What do you mean when you say you've tested the lambda probe?  How did you test it?

Pre-heater shouldn't really cause a problem as long as the exhaust is hot (do the emissions change much if you hold the engine at high revs for 30 seconds and then do the test again?).  To me, it does seem to be a sign that someone else has been having the same problem and has been messing about.  If the probe is an unknown then I'd just change it for a new one, it'll pay for itself in better MPG over time anyway.

[Andy]

I'd put a new lambda on and re-instate the cut wire. The pre-heater on the probe is there to get the probe up to operating temperature quickly and evaporate any moisture - the latter can quickly damage the probe.

[stuG40]

Finally getting back round to this after I got side tracked with starting problems.

Does anyone know if the BLACK wire shown the photo should be going into the terminal block at the ecu? The black wire should be an earth.

[hayesey]

I assume that cable with the purple & black wires in is coming directly from the lambda probe.  It doesn't look like a normal lambda to me, there is normally a cable like that coming from the probe to a connector mounted to the bracket on the inlet manifold.  They normally have 3 wires in, a 12v & ground (for the probe heater) and a single purple wire which goes to the ECU.  So this makes me suspicious of the probe you have on your engine, whether it's the correct one and whether it's wired up correctly.