Engine 850: B5254S/2.4/20v: MOT Lambda Problem?

[myshed]

Vehicle just SAILED through Mot - apart from Lambda results - and advisories that brake pads are wearing a bit thin - at minimum 5mm, and NO warning lights!

It's the Lambda issue that's worrying me.

Have checked back over last 4 MoTs, and reading has deteriorated from about 1.02 to todays' at 1.041 (same last year's reading), covering a distance of some 36k. HC and CO readings have reduced over this period to 0% and 6ppm. Fuel economy good. Serviced about a year ago (inc new plugs & air filter which still appears new).

This lambda reading is just outside MoT limit of 1.03 - so vehicle has failed, and I need to get it back on road without too much delay.

Any suggestions? Don't really want to spend £couple of hundred a time swapping out sensors!

Thanks

[Chris_Rogers]

I'd suggest that you have a careful look at the exhaust for a small leak, probably near the tail pipe.

Readings greater than 1 indicate a weak mixture (excess oxygen), this may not be the engine at all but air (oxygen) entering the exhaust system.

[ewanc0]

I just did my own lambda sensor. Sensor was £79 and took me about half hour to fit. Not a difficult job.
Out of interest is your lambda light on? and have you had the codes read?

[myshed]

Fascia "lambda" light is ON - was before last MoT (year ago), but test reading then was just on limit (1.04), so MoT pass. Have the MOT changed limits to 1.03? vehicle test reading is identical to last year.

MoT examiner suggested the cause was probably an air leak downstream of the sensor, and this seems to concur with the "burbling" from the exhaust on over-run - but he could find nothing at all.

Not sure if I have one of those 850's which uses ODB socket just to highlight flash codes, or if it is fully compliant. Have tried using the "flash code reader for Dummies" featured on this site, but no flashes show. The LED lights up when connected for the 2-3 seconds but nothing after that. Does this suggest all is OK, or that vehicle is fully OBD compliant and that this code reader cannot work? 2.5/20v 1st registered 28 Jan 1997 - looks identical to that featured in "flash code reader for Dummies". If fully compliant, can anyone recommend an inexpensive reader?

Thanks in anticipation!

[Chris_Rogers]

Your car is OBDII compliant, this will work OK as a basic reader.

http://www.gendan.co.uk/product_GDEOBD.html

[myshed]

Well, Mot examiner could find no trace of an exhaust leak, neither during the test nor after when we "homed in" on likely causes of high oxygen.

Took car round to my local ATS; I was the only customer there at the time, so they gave the exhaust sytem a really thorough examination - absolutely no leaks, but could not explain the slight burble on the over-run. (They would not charge me a penny for their time, so a donation to Children in Need on its way!)

Could not locate a code reader very quickly (not until middle next week), so bit the bullet and took car to my local independent Volvo dealer, who were also extremely helpful. I did not see the code-reading, but they advise the cause of the problem is a "non-working air pump". Asked what this was, the mechanic advised that it drives the Secondary Air Injection System.

My Haynes manual is virtually completely silent on this, so any help advice information would be appreciated - can it be a fuse, or a blocked filter, can the pump be repaired, where is it, how much if I need a replacement - all that sort of stuff.

Thanks in anticipation

[Chris_Rogers]

http://volvospeed.com/Repair/airpump1.php

I doubt if the pump itself is the cause of you MOT failure but it may be useful to block off the SAS valve, if air is leaking in via the valve it would not be helping.

[Paul240480]

Going back to your exhaust:

They are very long lived on these models, one of the first things to 'go' is the baffles in the big silencer 'amidships'. Not an MOT fail (afaik), but does make the car sound a little more 'throaty' than is normal. Could this be the cause of the higher oxygen reading?

As for the O2 sensor itself, it is quite an easy replacement, as mentioned. I got mine from GSF for £39, it is an MTE Thompson make & made in Brazil! So far so good.

[myshed]

Originally Posted by Chris_Rogers

http://volvospeed.com/Repair/airpump1.php

I doubt if the pump itself is the cause of you MOT failure but it may be useful to block off the SAS valve, if air is leaking in via the valve it would not be helping.

Thanks, Chris - excellent link. I'll be playing with all this stuff over next few days as time permits, and will post outcome here

[The Hitcher]

Another link
http://www.matthewsvolvosite.com/200...utorial-volvo/