MOT, high emissions

Post Reply
Message
Author
colin33
New member
Posts: 195
Joined: Mon Jan 31, 2011 8:48 pm

MOT, high emissions

#1 Post by colin33 » Wed Feb 06, 2019 3:02 pm

My V6 petrol vectra normally has a co level of 0.49, and hc ppm of 0122 at MOT time. However, just scraped through this time with co at 3.47, and hc at 0255. Anyone suggest why my co has jumped so high? I have re calibrated recently, could it be that it's running too rich at idle/low revs?

Brian_H
Intermediate Member
Posts: 1348
Joined: Mon Jan 23, 2012 12:21 pm
Location: Milton Keynes

Re: MOT, high emissions

#2 Post by Brian_H » Wed Feb 06, 2019 4:53 pm

I'd take a look at the lambda sensor readings - live data your best bet, compare them on petrol and gas. If they are the same it may be a dodgy probe (output should fluctuate, it may either be slow to react, or stuck at a certain level), if its different between the two it may be a tuning issue of some sort. Also do a scan whilst your there for any other errors just in case they give a clue whats going on.

If you can post that sort of info back here, someone should be able to advise you if your not sure its how it should be.

Was it tested on petrol or gas, and was the tester set to the fuel being used?

LPGC
Installer
Posts: 3504
Joined: Wed Sep 29, 2010 6:01 pm
Location: Yorkshire
Contact:

Re: MOT, high emissions

#3 Post by LPGC » Wed Feb 06, 2019 6:56 pm

Hi Colin, Is this the same car as in the melted iridium plugs thread https://www.lpgforum.co.uk/viewtopic.ph ... 16#p112216?
Linked to the other thread because it will help recap with a bit of background info. Brian_H question about what fuel it what tested on (and tested on in the past) is a good one.
One thing that can give high emissions is if some cylinders are getting rich mixture while others get lean mixture. Lambda readings are average for the cylinder bank (not quite true but a close enough description for intents and purposes), so lambda can seem correct even with different mixtures to different cylinders. So, individual rich cylinders can give high emissions readings... But the rich cylinders may not actually be the cause of such problem. If there's a cylinder running particularly lean it will cause a lambda probe to read lean mixture, so the mixture gets richened up, so then you still have the faulty cylinder running leaner than the other cylinders but the other cylinders will be running rich.
Full time LPG installer
Servicing / Diagnostics / Repairs to all systems / DIY conversion kits supplied with thorough tech support
Mid Yorkshire
2 miles A1, 8 miles M62,
http://www.Lpgc.co.uk
Twitter https://twitter.com/AutogasSimon
07816237240

colin33
New member
Posts: 195
Joined: Mon Jan 31, 2011 8:48 pm

Re: MOT, high emissions

#4 Post by colin33 » Fri Feb 08, 2019 10:08 pm

Hi, thanks for your replies. Yes, this is the same car with the melted plugs, and all the other various issues I've had during and after installation about 7 years ago :-) Not all the issues have been sorted (I still occasionally get a 'small explosion' when starting after the car's been left overnight for example) This particular problem is much better since renewing the injectors, but it hasn't gone away completely. I replaced the iridium plugs with 'ordinary' ones and re-calibrated, and will check their condition after a few more miles have been completed. As for the emissions, the car was presented on lpg, as always, but I'm wondering if the analyser they use needs telling it's running on gas? I presume it would not, as the emissions still get read in the same way surely? Actually, the guy who carried out the mot was not my usual tester, and I'm wondering whether he inadvertently had the car running on petrol at the time. I reckon the readings are consistent with an old v6 petrol missing the catalytic converter don't you think?

Brian_H
Intermediate Member
Posts: 1348
Joined: Mon Jan 23, 2012 12:21 pm
Location: Milton Keynes

Re: MOT, high emissions

#5 Post by Brian_H » Sat Feb 09, 2019 12:23 am

colin33 wrote:
Fri Feb 08, 2019 10:08 pm
Hi, thanks for your replies. Yes, this is the same car with the melted plugs, and all the other various issues I've had during and after installation about 7 years ago :-) Not all the issues have been sorted (I still occasionally get a 'small explosion' when starting after the car's been left overnight for example) This particular problem is much better since renewing the injectors, but it hasn't gone away completely. I replaced the iridium plugs with 'ordinary' ones and re-calibrated, and will check their condition after a few more miles have been completed. As for the emissions, the car was presented on lpg, as always, but I'm wondering if the analyser they use needs telling it's running on gas? I presume it would not, as the emissions still get read in the same way surely? Actually, the guy who carried out the mot was not my usual tester, and I'm wondering whether he inadvertently had the car running on petrol at the time. I reckon the readings are consistent with an old v6 petrol missing the catalytic converter don't you think?
No they will need to set the tester to the fuel as the test depending on fuel is slightly different, something to do with the HC needing to be calculated differently (Hexane rather than something else i can't remember means you'd have to divide the result for hc to get the correct value, I can't find exactly what now, but know thats what the MOT tester that used to be my neighbour said if the machine didn't do it automatically you had to do)

Typically you shouldn't have a lambda value shown if its set to gas on the emission test certificate, if you have it.

CO is still too high either way, but wouldn't be surprised if that was down to a leaky petrol injector as a possible cause (you wouldn't normally expect to see much CO from running on gas).

Your small explosion might be a sign that the inlet manifold is filling with gas when its switched off, suggesting its leaking somewhere - Given the other bits you mention, I'd have a look over your vapouriser and verify it isn't leaking gas through its vacuum connection if you haven't already ruled it out, Would hope that a new set of injectors wouldn't leak! Suppose the same is also possible if a petrol injector is leaking though - best bet may be to let it sit overnight and then have a look past the throttle area and see if you can smell petrol or gas there (one or the other must be present to cause the explosion, and that might also be where you need to be looking for the high CO/HC readings as if its leaking when stopped, its likely leaking when running as well). That might also explain the melted plugs??

colin33
New member
Posts: 195
Joined: Mon Jan 31, 2011 8:48 pm

Re: MOT, high emissions

#6 Post by colin33 » Wed Feb 13, 2019 10:18 pm

Hi Brian, the test sheet says 'lpg' but I wonder whether the car was actually running on lpg when he did the emission test. Mine is set to switch over at 1600rpm and it's possible that this didn't happen (after the obligatory time delay)
We covered the explosion issue in another thread, and came to the conclusion a leaky injector was the most likely cause. However, new injectors, and it's still happening but far less frequently. I haven't looked at the possibility of a leaky vaporiser though, so maybe this should be my next step. It's a 'magic 3' ...

Brian_H
Intermediate Member
Posts: 1348
Joined: Mon Jan 23, 2012 12:21 pm
Location: Milton Keynes

Re: MOT, high emissions

#7 Post by Brian_H » Thu Feb 14, 2019 12:59 am

There is a fair chance your right there. You should be able to test vapouriser by disconnecting vacuum line and putting the end leading from the vapouriser into water, like your locate the leak in a bike inner tube. If it bubbles then its leaking might only be a very slow leak.

Post Reply