Xantia failed MOT on emissions - what now?

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samtronic
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Xantia failed MOT on emissions - what now?

Post by samtronic »

Hi,

I just had my Xantia (petrol 1.8i 8V 1993) to the bi-yearly MOT and it failed on emissions with a CO reading of 0.7% (the limit is 0.5%).

Is it most likely the catalytic converter or the lambda sensor (or connections), both or something else?

For some reason a catalytic converter would cost me DKK2050+moms (~£230) in Denmark while I can find them on the net for £50-100 in UK...

The car is otherwise running fine and not using any oil. But I guess oil usage could give elevated HC readings - not CO?


Regards,
Søren A.M.
'93 Xantia 1.8i 8V
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Post by CitroJim »

The CAT or the lambda is a likely candidate here. If the Engine Management light is off then it is more likely the CAT :( If it is the original then it will be very near the end of its life. A duff lambda will give itself away with a bit of rough running.

A quick (and very rough) check is that a CAT equipped car should run with a totally clean tailpipe. If it is sooty then the CAT will be prime suspect.

Before you go changing it, if you have not done so, give the engine a full service, including filters, and check the pipe to the MAP sensor. These can perish, leak air and cause high emissions. It is worth checking the whole inlet tract for air leaks as well. Air leaks are terrible for upsetting the fine balance of the engine management.

Are you able to have the emissions checked before you take it back for a full retest to see if all is OK?

High oil consumption would poison the CAT by covering its active surfaces with soot and by-products of the combustion of oil, some of which are harmful to a CAT. This would in turn up the CO and HC. If you cannot see visible smoke and you have no or negligible oil consumption then this is not the problem.
Jim

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samtronic
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Post by samtronic »

The engine manegement light is off and there was no error codes stored in the ECU.

I have just measured the signal from the lambda sensor after cleaning the connectors and tracing the connections to pin 10 and 28 in the ECU connector.

The signal is changing between 0.2 and 0.8 V and back in ca. 3 seconds and staying low or high for 0.8-1.5 second. This is at idle with a hot motor, when the motor is cold it is a bit slower.
If the info here is correct, it looks like the lambda sensor needs changing.

It does idle (and run) pretty smooth though.

The tailpipe is a bit sooty, so a new cat is probably also needed... And it is only 2 years ago I welded a new piece of pipe on...

I hope to get access to an emission tester before I try the MOT again - I hate to change things without knowing if it helps...

Regards,
Søren A.M.
'93 Xantia 1.8i 8V
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Post by CitroJim »

Søren,

That is an incredibly useful site. A good find!

I'd agree the lambda sensor is getting sluggish and of course, because it is working, even if not very quickly, the ECU thinks all is OK.
Jim

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Post by citronut »

i was told you can somtimes clean lambda sensors with carb cleaner,if you have welded to the cat this can damage then,also you should never use exhaust jointing paste at the front end of a cat,
regards malcolm
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Post by micitroen »

Still worth trying a change of oil and filter, I always do mine before an MOT.
Mike



1993 BX TXD EST mmm. nice. 1990 Bx 19TZD Auto Lhd (now lives in France) 1998 Xsara 1.9d lx.
samtronic
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Post by samtronic »

Thanks for the help and suggestions.

I have ordered a new lambda probe from eBay - Eur 59,- incl. shipping. Hopefully I get it before the weekend and hopefully I can find an emissions tester by then.

I think it sounds plausible that a slow lambda probe could lead to elevated CO emissions because when the mix is richer than normal, the cat can't do much due to the lack of available O (or NOx ), but when it is lean it works fine.
And when the lambda probe is slow the mix gets richer when it is rich.
But then again, I might be wrong. :)

I found the cat cheap (£46.49 + vat) on the web, but they won't ship it outside UK. :(

I intend to change the air filter (although it is not terribly dirty).
The oil (and filter) was changed a couple of months ago.

I can get an universal cat for 700-800 dkk (£65-75), but I have no idea if they work ok. And then I would have to weld it to the old pipes. And get it to fit.


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Søren A.M.
'93 Xantia 1.8i 8V
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Post by CitroJim »

samtronic wrote:I think it sounds plausible that a slow lambda probe could lead to elevated CO emissions because when the mix is richer than normal, the cat can't do much due to the lack of available O (or NOx ), but when it is lean it works fine.
And when the lambda probe is slow the mix gets richer when it is rich.
But then again, I might be wrong. :)
Sounds spot on to me Søren :D

The universal CAT should not present any problems. Someone who is handy with a welder should have very little problem in making up a set of adaptor flanges to take a universal CAT even if yours, like mine, is actually part of the front downpipe. A company that produces or fits custom performance exhausts and "Decat" pipes should be able to do this work.
Jim

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philhoward

Post by philhoward »

citronut wrote:i was told you can somtimes clean lambda sensors with carb cleaner,if you have welded to the cat this can damage then,also you should never use exhaust jointing paste at the front end of a cat,
regards malcolm
The one I heard was using a propane (NOT BUTANE) blowlamp to clean the deposits, and also to check it. Never tried it myself though..passed the info onto an ex-work colleague who was having Lambda issues. He then proceeded to remove the sensor to do the check and heard rattling bits. No need to test that one!
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Post by slim123 »

It's only a little high, I would run to about 1/4 tank of fuel and then add 2 x bottles of fuel treatment type stuff, good results I have had from Forte and Wurth, but I guess that it's all near enough the same.

I bet it will bring it down to limits :twisted:

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Post by citronut »

the diesel guy in the local LSUK diesel shop dose not recomend the fuel addatives as he said they are abbrasive and can cause more harm than good
regards malcolm
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Post by slim123 »

Sorry to disagree, but I can only recall good results both on Petrol and Deisel cars, I would like to know where the evidence comes from. (perhaps it's a ploy to stop diy!!!)

Regards
Slim.
samtronic
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Post by samtronic »

Hi,

just a follow-up:

The lambda probe I bought on Ebay was incorrectly wired (swapped wires on the sensor plug) and the plugs was very tight - I needed pliers to get them to mate. Next time I just buy an universal one and use the old connectors - like I ended up doing anyway. And universal types are much cheaper - like 30 Euros shipped.
But the probe works much better than the old one - in idle I can actually see the signal from each cylinder as dips or peaks in the overall signal, which changes from low to high and back to low in 1 sec.

I got an universal CAT and fitted it without any major problems - as the pipes was a bit smaller and the CAT a bit shorter I nedded to cut some more pieces of pipe to make it fit. I got one of my friends, who is a professional welder, to weld it and it took about 15 mins.

The core of old CAT was partly eroded and probably very dead.

And just to be on the safe side I changed the sparkplugs and the air filer.

It passed the MOT this time with a CO reading of something like 0.01% in idle. :D

Now I have lots of time to fix all the small things like the rear left ABS sensor...


Regards,
Søren A.M.
'93 Xantia 1.8i 8V
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