Emissions

[Silentmonkey]

Just had the wifes Astra fail its MOT on emissions and was wondering if anyone here could shed some light on the possible cause.

The only thing that is wrong is high CO at fast Idle.

The Results

Description	Min	Max	Actual	Pass/Fail
Fast Idle Test				FAIL
RPM	2750	3250	------	Not Checked
CO %vol	----	0.300	0.455	Fail
HC ppm Vol	----	200	33	Pass
Lambda	0.970	1.030	1.010	Pass
Second Fast Idle Test				FAIL
RPM	2750	1050	------	Not Checked
CO %vol	----	0.300	0.355	Fail
HC ppm Vol	----	200	30	Pass
Lambda	0.970	1.030	0.999	Pass
Natural Idle Test				PASS
RPM	750	3250	------	Not Checked
CO %vol	----	0.500	0.237	Pass
Overall Result: Exhaust Emissions Test				FAIL

As the CO is just over (BTW the car was hot) and since Lambda and HC are well within spec's I'm guessing that fuelling is correct and that the CAT has failed but I'm open to cheaper suggestions!

Edited by Silentmonkey on Thursday 15th October 16:50

[syncro.]

I think you're right! Looks like the cats past its best, you could try getting it red hot before the test to eak it through 1 more MOT but it'll definitely fail the one after that!

[skid-mark]

you can see on the second fast idle test the reading is lower so it was going down, probably find cause it's the wifes car it just gets potted about, so if i was you i would give it a good run with lots of high revs and let it clear the cat out and make sure your car has had a good run before your retest so the cat is really warmed up.

[Silentmonkey]

The tester was giving it plenty of beans between the tests to get it warmer. So he was batting on my side. I was going to change oil and filters and give it an "Italian service" before the retest. Maybe some additives too. Anyone tried CataClean?

Edited by Silentmonkey on Thursday 15th October 22:48

[ridds]

I'll put money on the Cat not being hot enough.

There's giving it beans and giving beans correctly to get it though the test. Some older cats with failing cats can be tricky.

My old Audi Coupe sat up at 0.750 CO for ages then when the revs were let off a little it plumeted.

In all honesty I'd try another garage first 0.1% is not a lot and probably within the tolerances of the machines.

[Simon Says]

From my experience of cars failing the cat test is as follows,most cars with failed cats and everything else functioning correctly reach CO 0.4/0.55 approx its the Cat influence that tightens up that last bit and bring the readings down to <30 if you are getting readings of i.e 1.0> then you have other problems like failing/lazy Lambda/Oxygen probe/s this is a basic description but works most of the time,although i think the OP's problem was the cat was not up to temp far better to give the car a blow out on the road 1st than try and blow out on the ramp when you cant put the motor under load to get the temps right up,dont shut the motor down while your waiting to get on the MOT testers ramp either(keeps everything nice & hot)

[Silentmonkey]

I gave the car a service last weekend. New oil, oil and Air filters. I also cleaned the throttle body which had a blocked jet. Did the "Italian service" just before the re-test. Up and the A5D in third @ 5500 rpm fo 10 mins before and it Passed(just)!!!! CO now down to .255

I know it will fail again next year but we will have owned it 12 months in Dec so its off to the dealer early next year for a £2k trade in.

Thanks for all the advice.

[Shoot Blair]

Whack some ethanol in it to take the C:H ratio down enough to get it running cleaner. 50% ethanol, 20% celly thinners. Done