Emissions failure (MOT)
 

On the BiFuel I see there are 3 Lambda sensors. 2 normal ones and 1 specifically for the LPG system?
On MOT test, running on petrol, idle lambda and gas emissions were steady but at 3000rpm everything was fluctuating and this produced a fail.
I didnt get the chance to test on LPG.
I remember on the previous test the Inspector getting agitated with the readings BUT he passed the car, may even have over ridden the machine.
Now that was with a new front pipe and CAT fitted. The other I took off because it was rattling inside. I still have that pipe in my scrap pile.
I see there such things as 200cell CATs but they only seem to have 1 sensor point.
Any opinions please?
Gazzer

Hello there , If you are having issues with emission issues when running on petrol , pop into your MOT place ( if you can ) and ask them nicely to perform a free reading test , just to show you exactly what is being recorded by the machine .

If you still appear to have problems , send your car for test RUNNING ON LPG & inform the tester it is running on LPG . There is a different criteria for LPG emission readings , I get this sometimes on petrol , fails & always pass when tested on LPG .

With regards to number of Lambda sensors , simply buy as many additional bosses as you need , drill & weld onto pipes to match original set up making sure there are NO leaks as this will affect lambda readings, so you can happily use a 200 cell Cat . Also take your car for a good thrash before presenting for test, we get many that fail emissions testing as they drive very short journeys / never get hot /bimble around at 9 MPH & the cat is unable to obtain working temp , becoming unable to function correctly . A "drive it like you stole it " journey should generate sufficient heat to allow the Cat to begin functioning

Good Luck :)

dingov70: Thanks for coming back.
The test is taken in Spain. The only difference is I take the car through under the instruction of the tester (same as HGV in the UK). The tester sits in the car to do the emissions part of the test.
I watch the screen for results. The idle speed is fine. At the 3000rpm test, the figures constantly fluctuate (just like the primary lambda sensor does) but as I said, this was on petrol. Im not sure what my rights are to insist on LPG test. IF the petrol lambda sensor is wonky (lazy as they can get) then the LPG lambda sensor (which is the one on the down pipe I assume) is different to the other two.
Although I was not exuberant driving the 45km to the test centre I did run the engine for at least 15 mins prior to going in for test. The engine should have been at working temp. HOWEVER, there was moisture coming out of the tailpipe (it was a cold day).
It's the fluctuation that confuses me...and the tester!
Ive been lucky, just like many others, there are NO tests at the moment...but not for ever! It failed at the beginning of March!

UM ! , I would ask very nicely if they can point you to the ITV test manual , so you can read that . This is a freely available on line manual in the UK .

I would find someone with a diagnostic machine & perform a live data read , all the better if driven on the road , you can actually see the values the lambda sensors are returning & which one is dying / faulty .

You may could also simply ask the ITV examiner about testing on LPG , they might well be happy to do so

Just found this , it may help you

https://itv.com.es/

I drove it like I stole it before the test and then sat for 45 mins before I got called in!
On the emissions side, rev to 2500 rpm and it settles on 0.04% contaminantes and 1.010 lambda. It was a bit fluctuating before hand but the tester was happy at the figures given.

The SRS was fine.

Passed! thank you all.