Failed MOT on emissions

[cyclogenesis]

Any ideas?

850 T5 with BRC sequential conversion failed MOT on emissions today. Could the failure of the CAT push the levels above the limit in any way? This is what the garage thinks but I am a little surprised. Could a corrupted CAT be pushing out noxious gases that raise the levels and mask the low CO of the LPG. I have checked the codes on the Unleaded system and nothing found. Lambda and MAF fine. Car runs fine on both systems and LPG filters changed only this last weekend.

A bit stumped as I though the LPG would always give a low reading to pass.

Before you ask, yes the tester did do as he should and tested on LPG but it failed.

Any ideas?

[cyclogenesis]

sussed it. One of the vacuum hoses had come off the inlet manifold. I had white smoke before, now it has gone. Fingers crossed for re-test

[dingov70]

Hello there , when you presented your car for test was it running on LPG or petrol ?? . The reason I ask is that you test " as presented" BUT you have different values allowed when running on Lpg

Limits for LPG are CO Under 3.5% HC under 1200 ppm . If the gas analyser was set to test for petrol you will fail the test even with a fully functional cat .

Another good thing is to drive at speed in a lower gear & get the revs higher than normal , this raises the exhaust gas temp & will burn off or reduce any crud on your cats matrix , which should help it work more effectively .

ring test station & ensure tester had gas analyser set for LPG , if they cannot confirm it was set correctly , ask politely if they will do a gas reading with the car running on Lpg .

Hope this helps you

[cyclogenesis]

Thank Dingov,

Yes they had done it correctly. I have the readout it was up at 4%. In an effort to get it to pass they even tried doing an unleaded only test which failed also, that's what led them to think it was the CAT.

I drove it and noticed a lot of white smoke coming from the exhaust. I had a similar issue some years ago with a diesel A4, pumping out black smoke on acceleration and noticed that an intake hose was split, allowing in un-metered air. I did some driving tests in the 850 and could hear some whistling, so checked under the bonnet and the vacuum hose that goes to the inlet manifold was off. (must have knocked it when I cleaned the idle valve). Drove again and no smoke so its booked in again for Friday and I hope it passes.

Cheersnow

[dingov70]

Nice one , lets just hope the free fix cures & you get a pass certificate

I would definately give it a fast run in a lower gear simply to raise gas temps & burn off any deposits that might also be hindering the cats functionality .

Had a few that respond very well to a yob tune , leave Blackpool on M55 in third drive to Preston & return in 4th gear . Bingo readings plummet

Was once stopped by Plod on M55 as they wanted to know why the car was "racing " , i explained & they left me to it

[CNGBiFuel]

If that hose is giving you issues, I've a fiver that says your PCV is not far behind. Do the glove test on your oil filler cap. Google this, PCV can be a killer.

[cyclogenesis]

All sorted. There were two hoses off. One going to the manifold and one that goes to the bottom of the intake pipe just before the turbo. Fixed both in place and it passed with flying colours.