Xantia emissions failure, comments and help please

reffro · Post by **reffro** » 09 Jul 2003, 21:57

Hello all,
a short while back I was in a quandry about the emissions on my Xantia ('94 2.0 VSX 8v Auto). It had failed to pass its emissions on the MOT despite having had a catalyst replaced less than 16 months previously.
After following the suggestions of unplugging the battery to re-set the ECU, giving it a good run before the test, getting it nice and toasty, 90C Water temp, 95c Oil temp when I retested it it still failed. Since then I have had an oil change done even though the oil that was in was only 3 months and 3000miles old. I've had the ECU plugged into the diagnosis equipment, no fault codes, and the air mass and lambda sensors both seemed to working correctly, they were both varying their readings as the revs rised and fell.
The emissions themselves were all OK except the CO readings being slightly over the limit 0.34 v <.03, HC were 17ppm v <200pm and the lambda value was 0.987 v 0.97-1.03. Is there anything else that could cause the failure apart from the Cat. Its certainly not running rich with that low HC reading.
The only reason I ask is I'm about to get the Cat replaced before another re-test. Have I missed anything obvious here, before I get it done????

Post by **RichardW** » 10 Jul 2003, 02:00

High CO means not enough oxygen to convert everything to CO2, so it IS running rich (also given away by the lambda being <1). It's not much over, so it could be your cat (unlikely to be the temp sensor as it would be way out), but given it's only 16 months old, I don't think so. Try taking it to an injection specialist and getting them to test the lambda sensor with an oscilliscope, I think you might find this the cause of your troubles.
Richard

mbunting · Post by **mbunting** » 10 Jul 2003, 02:15

I presume you've changed the air filter, and checked that the inlet piping is leak-free ?

wheeler · Post by **wheeler** » 10 Jul 2003, 04:26

when you say the readings were varying as the revs raiesd & fell are you saying the signal voltage went up when the revs went up & down when the revs went down ? if the sensor is working correctly when the engine is warm and at idle the signal voltage should constantly fluctuate up & down between aproxx 100 - 800 milivolts (or 0.1-0.8 volts)

reffro · Post by **reffro** » 10 Jul 2003, 14:47

I don't remember the exact values but the variation between 100-800 mV seems correct, I certainly saw 200-650 appear on the technicians display. I am concerned about the cat though, as it may have been contaminated inadverantly. Little did I know but Citroen printed the wrong value in my manual for oil and filter change re-fill values. So I have been overfilling the car with 1 litre of extra oil in at least two seperate occassions. Not happy about that but that's what happened. The air and fuel filters are 8 months/9000 miles old, as are the spark plugs. I will get the injection checked though, as there is a lot of soot in the exhaust tail pipe, which suggest the car was running rich, but as the HC value was so low I didn't think that would be the case.

Sl4yer · Post by **Sl4yer** » 11 Jul 2003, 21:45

Did it fail on both natural idle and fast idle, or just one of the two?

Homer · Post by **Homer** » 11 Jul 2003, 22:51

My fathers Xsara failed on emissions due to a leak between the exhaust manifold and the exhaust. This was sucking in air so the lambda sensor was getting a (false) high oxygen reading so the engine management was compensating for it by running rich. (I think)
You <i>might</i> expect a leak at that point to blow out (I did) but the moving gas inside the pipe causes a bernoulli (sp) effect (the thing that makes planes fly) and sucks air in.

reffro · Post by **reffro** » 11 Jul 2003, 23:36

Originally it failed on the fast idle test only, the natural idle was ok.
Anyhow it passed today..........
I checked everything, used all the advice I had been given, and with the help of kind MOT tester who gave it a bit of helping hand on the emissions test, no cheating, but a bit of variable throttle pressure sorted it.
I had since the last test had the oil changed, and on the advice that a dirty air filter might cause trouble just took the thing out for the test. The readings where as follows, fast idle, CO 0.28, HC 11ppm and lambda 0.993, the slow idle was CO 0.45 v <0.50 limit.
So thank you one and all, just hope this isn't going to play out this way next year.

Sl4yer · Post by **Sl4yer** » 12 Jul 2003, 02:11

Good result, and keep at it. I'm guessing the problem can't lie in the cat if it has passed this time [8D]