Our Jazz just passed (of course!) its 6yr MOT.
I noticed the HC reading on the emissions increased from 6 last year to 95 this year. Other reading were perfect - 0 for CO and 1 for lambda.
Limit for HC is 200 and I realise this is PPM, but the numbers mean nothing to me - can someone explain likely reason for the increase?
{Guessing the year is 2003 and not 20? }
Edited by Dynamic Dave on 11/09/2009 at 01:59
|
Could be something as simple as you bought some contaminated fuel with an extra dolop of water in it
im sure if the engine had been fully warmed up prior to the fast idle test your results would be minimal again
|
Thanks - it does always use Shell rather than supermarket stuff although I realise that's no guarantee.
The engine ought to have been pretty warm - it had a 10 mile run before it went in so wouldn't have taken much warming up even if they left it for a while.
I was wondering how easily the reading could increase by what seems like a big number? The same again would have it borderline for failing.
Edited by Bill Payer on 09/09/2009 at 15:28
|
Rightly, or wrongly, I'd always thought that the HC component of the MOT gas test was effectively an indication of increasing amounts of oil being burnt.
I.E. the engine is beginning to wear (a bit). - be it oil seals, bore wear, or whatever letting a bit of oil into the combustion chamber.
Another variable (may well be) the specific test machine, or its nozzle:
my Punto was MOT'd this morning, and the SUN test machine took some sorting out after the previous car (which failed on emissions) had effectively coked up the sensor nozzle.
(lots of cleaning and a re-boot or two, by all accounts).
All the above maybe nonsense - I am not a mechanic.
|
Rightly or wrongly I'd always thought that the HC component of the MOT gas test was effectively an indication of increasing amounts of oil being burnt.
What are you saying - a Honda Jazz burning oil!!! For the record, it never uses a drop between services.
Another variable (may well be) the specific test machine or its nozzle:
It was done in the same garage but I guess there are a lot of variables. Certainly a different tester, the engine may not have been run at the same speed (don't know if that's an issue). Perhaps they just do a rough test (engine not hot etc) and only worry about the details if it fails.
|
|
|
|
|
Every spark ignition engine misfires a certain amount. As the plugs fur up they might miss a little more:) Have they been changed on schedule? The rear 4 of the 8 in total are a little inaccessible, I believe.
|
Have they been changed on schedule?
Well, they were changed at 28K miles and the car has done 40K now. Schedule on this model is every 25K miles.
The HC reading 2 years ago, at 28K miles (but no idea if before or after plugs were changed) was 28. That MOT was done at a honda dealership.
|
Perhaps it's running a tad rich, any change in the fuel consumption. Has the air filter been changed lately, breather hose partially blocked....or whatever recirculates crap from the top of the engine back into the inlet.
Unlikely to be wear on something like a Jazz.
I doubt the plugs are causing a misfire, if they were you engine/emissions light would come on as any misfire fairly quickly damages the catalytic converter in the exhaust.
|
|
tinyurl.com/njy8me Look at page 9 which illustrates "combustion chaos" in a normal petrol engine. Obviously there are degrees of misfire. Every partial combustion event means fuel is unburned: it doesn't take much to raise ppm from 8 to 28:) As 1% is 10,000ppm, the issue here is probably more about testing repeatablity than an actual problem.
|
|
|
|
|
