MOT Emissions Failure

Mr_Stroudley

Yes, you sum up the situation very well 5tide. I'd just had a major service done prior to the MOT and phoned the guy who did it (he does them all, well nearly all). He offered to do just that (ie check the emissions again) but was going away for 12 days holiday the very same day! So he's my long stop. The old MOT will expire very shortly after that though and I'm really looking for something positive in the meantime, ie that an MOT emissions failure printout should have something more than "0" against all the CO and HC readings! Any takers? Please....:)

mikey72

Lambda is a calculated figure, from the measured gases. I find it surprising they can calculate it if two of the figures are zero.

atrixblue.-MFR-.

fivetide wrote: »

I'd have expected a failed lambda to chuck up some sort of fault either the engine light or an exhaust one (if your car has it. Certianly on a 2003 Civic I'd expect the ecu to be checking things like that.

A good vote for the 'italian tune up' did you watch them do the test? was the car really hot when they did it? Things like that make a huge difference of course.

I'd be tempted to see if someone can check the emissions for you without actually doin the MOT test. If it proves to be good, then as you say, you can confront them with it and see what they say. If there are no faults showing up on the car, I'm not sure what difference plugging it into a laptop would do either, presumably it will not report a fault to them so the diagnostic seems a bit silly.

If the cat was blocked the car would not be running right I'm sure. The two times I've seen that it has been blockign the exhaust and stalling the car, bit like the old 'banana in the tailpipe' from Bevverly Hills Cop.

No harm in a second opinion really.

5t.

actually plugging in a propper odb2 fault code reader would be able to tell you what your lambda sensors are doing with a live reading, ive seen this test in action, and proved a faulty sensor eventhough EML problem hadnt arose on the dash in a 2006 golf gti (we all know how tempermental golfs get when something is amis).

Mr_Stroudley

Ah! That is interesting mikey72! If that is so then how could they generate such a printout? I've just realised that I didn't answer fivetide's question re observing the MOT. No, I didn't as I was told that the MOT would take one hour, and that there was an additional free "Safety Check" that would take 30 mins, and the car would be tested in about 20 mins time! So I wandered off around town returning about an hour and a half later to be told that the car had just failed the MOT (the free safety check was not carried out either). It may or may not be pertinent but the MOT was paid for with tokens issued by Tesco from Clubcard points, the chain in question has just changed hands and the branch had a new manager. I have used the previous incumbents on the same basis with no problems, but plus ca change.....!

PsiDOC

mikey72 wrote: »

Lambda is a calculated figure, from the measured gases. I find it surprising they can calculate it if two of the figures are zero.

Because the Lambda is measured from the oxygen content in the exhaust not the CO, CO2 or HC. Ideal is 1.0, or 1% in real money, and this what your car aims for as optimum mixture burn. Anything between 0.97% and 1.03% will pass MOT.

As a footnote: The lower the lambda - or oxygen content the richer the mixture.

Psi

mikey72

PsiDOC wrote: »

Because the Lambda is measured from the oxygen content in the exhaust not the CO, CO2 or HC. Ideal is 1.0, or 1% in real money, and this what your car aims for as optimum mixture burn. Anything between 0.97% and 1.03% will pass MOT.

As a footnote: The lower the lambda - or oxygen content the richer the mixture.

Psi

No, it's a complex calculation based on 4 gases.
Oxygen is just one of them.

Carbon monoxide
Hydrocarbons
Carbon dioxide
Oxygen

Mr_Stroudley

Is it possible then that the only way to record zero CO and HC and yet a high Lambda Number is to not push the probe into the exhaust, perhaps even holding it clear of it? Lots of air so a high Lambda reading but no detectable CO or HC? I'm not saying that this is what happened, merely trying to make sense of the printout.

mikey72

I suppose it could be possible.

What were the figures for the rest of the test?

Mr_Stroudley

Other than the appropriate limits being listed, there were none. Engine Temperature = Manual Check; Fast Idle Engine Speed (twice) = Manual Check; Natural Idle Test Engine Speed = Manual Check. Mind you, I had much the same on previous printouts at the same branch. The difference this year being CO and HC Fast Idle "0", and Natural Idle CO "0" as well as the two out of limits Lambda readings of course.

Mr_Stroudley

A quick update which is somewhat overdue, sorry! My car was given an independent diagnosis and all OK. Then put it in the same day for another MOT (at Just MOTs) and again OK. Contacted the HO of the original chain and after much haggling (Diagnosis and passed MOT costs plus free MOT; Costs, MOT and Interim Service), I finally accepted costs plus a Major Service for free. They didn't admit fault of course, but I did say I would never go to them for another MOT, free or Tesco vouchers notwithstanding.