My Scoob had its first MOT today and failed on the fast idle emissions test. It is a MY99 Turbo and the only modifications are a Magnex bacbbox, Magnex centre section and a panel filter. Since it still has a catalyst in the downpipe I was under the impression that it should pass. The fast idle emissions were as follows:

CO 2.43 max of 0.3 required to pass
Lambda 0.937 pass is 0.97-1.03

On Power Engineering's rolling road last November the CO was <0.1. Given that it is failing on the lambda readings, which I assume would be unaffected by the removal of the rear catalyst, I am wondering if something else is wrong.

The MOT tester thought the engine didn't sound right, although he wasn't familiar with Scoobs, and commented that it didn't pick up well when he was manoeuvring it. He may have a point since when I was driving yesterday it hesitated a couple of times on light throttle around 2500-3000 rpm, although it may have been my imagination. Also when I accelerated up a slip M-way road it wouldn't gain at all on a Honda Accord Type-R, which is about a second slower from 30-70 mph.

Could someone give me some advice on whether or not anything is wrong with my Scoob or if I should have it retested with the rear cat back on.

Alan

Plugs and plug gaps? Lambda sensor dodgy? Car nicely warmed (ie thrash the nuts of it) before test? I am not an expert just a few ideas.

Am I correct in thinking that the absense of a rear cat should not affect lambda readings, and since it also failed on these, there is probably something wrong with the lambda sensor or something else wrong?

What does lambda sensor do anyway?

Alan

Lambda is the measurement of oxygen. Needed to get the mixture right for the catalyst.
So, yup, if the lambda sensor isn't working properly, the engine won't be getting the right mixture & the catalyst can't do its job.
That's a bit basic, but, well, there you go!

Wifes Polo failed emissions for Lambda reading due to cracked weld around backbox.
Just a thought but could your lambda reading be due to poor seal between downpipe and centre section or centre and backbox?

Mike

Johns right, with only the cat in the downpipe you have to get it real hot before testing.

Good excuse for a blast around the block!

Jmca

I spoke to someone at Power Engineering on the phone today about my problem. He said the rear cat is the secondary one and thought it should pass without it. Therefore, with regard to your question it would be worse without a downpipe cat and with a rear cat.

With regard to my problem I can't see how the absence of the rear cat would affect the lambda readings, so there must be something else wrong, possibly the lambda probe. That would could richen the mixture and increase the CO. Then again I could be talking rubbish!

Alan

Lambda should pulse approx every 2 seconds with a reading of 600-700mv at idle.
If it's reading say 300mV the ECU will try to richen things up.
If it's not pulsing at idle then it's fit for the bin.

If the heater element within the Lambda has gone open circuit then the Lambda may not be getting hot enough during the MOT session to work efficiently.

Mine failed Fast idle due to O/C heater element.

If you had a John Banks special AFR, or a Dawes AFR this would confirm things.
Alternatively measure the Lambda input to the ECU with a Multimeter.

Sounds obvious ...but most grey import specialists who do MOT's will be very used to emission fails and often have more ideas in making adjustments to enable compliance. I hope you can read between the lines here.....

Best try one of them

Julian

Scott and Julian

Thanks for the suggestions. I have booked my Scoob in at my dealer next week for them to have a look at it. I would hope they should be able to diagnose any problems with the lambda sensor, but at least I am now armed with better information on which to query them. I have just extended the waranty so hopefully this should cover the repairs.

I have just been reading the Haynes manual for my previous car, a 1992 Nissan Primera eGT, which is fitted with a single cat. It states that the CO emissions should be much less than 1%. Well if my 1999 Scoob with one cat is giving 2.3% there must be something wrong with the Lambda or the main cat.

Alan

Alan,

Interesting what PE said. Regarding the Lambda! I tried mine with a DVM & could only get around 300 - 400 mV generally at idle. I also tried the heater wires by connecting an ohmmeter between them & could get nothing. So I'm assuming there's a fault or a breakdown in the element maybe.

Regards

Johny.

Alan - coincidence you post that!

I am wondering the same thing about the lambda. Had the emissions checked there & the Lamda reading was just under 1.

However the voltage reading of the sensor was about 300mV, which to me sounds as if it was lean - causing the ECU to richen the mixture. Would it not cause the Lambda emissions reading to go higher.

Is there any relation or what might be the relation of the ouput voltage to the emissions tester reading?


How would it do with just the centre cat & without the downpipe one.

Is the dowpipe really hard to change? If anyone has any pointers for changing it - it'd be really appreciated.

Regards

Johny

Edited - just read the post on changing the downpipe! Opened my mouth to soon.

[Edited by jmca - 3/12/2002 1:17:48 PM]