Failed MOT advice (Emissions)

[JamesV6CDX]

Very pleased with the MOT result. I expected a fail , and there were very few items in the list:

Exhaust has a major leak of exhaust gases (7.1.2) - expected

Exhaust emissions hydrocarbon content after 2nd fast idle excessive (7.3.D.3)

Nearside Front Lower Front suspension has excessive play in a lower suspension ball joint (2.5.B.1a) - Easy

Offside Front Tyre has a cut in excess of the requirements deep enough to reach the ply or cords (4.1.D.1a) - Easy


My question is - emissions?

Would the holed mid section in the exhaust cause this?

I thought with HC, it was usually unburnt fuel 

[aaronjb]

If the hole in the exhaust is before (or very close to) the primary O2 sensor then yes, as the O2 will read lean and the ECU will add ever more fuel (in reality making it run rich). If not then no, in fact it should make it look 'lean' on the emissions test (low lambda) but with normal HC & CO readings.

[JamesV6CDX]

The reading was literally just out of spec

Tester insists it's the exhaust

[b4ndit]

I would agree it is the exhaust had it many times doing mot's changed/fixed leak and straight through

[Kevin Wood]

I'd be surprised to see a HC failure due to a leak on an Omega unless the leak is pre-cat.

You never know, though.

[JamesV6CDX]

I'd be surprised to see a HC failure due to a leak on an Omega unless the leak is pre-cat.

You never know, though.

This was my instinct. Especially with the leak in the centre.

But he assured me with a new exhaust it will pass 

[Bigron]

James, if a new/repaired exhaust doesn't do the trick, I've had good results, emission-wise, with Cataclean, Shell V-Power and an Italian tune up!

Ron.

[Marks DTM Calib]

I'd be surprised to see a HC failure due to a leak on an Omega unless the leak is pre-cat.

You never know, though.

This was my instinct. Especially with the leak in the centre.

But he assured me with a new exhaust it will pass 

Cant see it, if it was Lambda it might.

I would be checking ECU coolant temp reading and breathers as a starter

[Automaticman]

My Frontera V6 only just passed the emissions with 30k genuine miles and a healthy exhaust, the boys at Vauxcare said they put Catclean in to squeeze it through 

[henryd]

I'd be surprised to see a HC failure due to a leak on an Omega unless the leak is pre-cat.

You never know, though.

This was my instinct. Especially with the leak in the centre.

But he assured me with a new exhaust it will pass 

Perhaps he ticked the wrong box at test and it did fail on Lambda,whats the printout for emissions look like ?

[Kevin Wood]

I'd be surprised to see a HC failure due to a leak on an Omega unless the leak is pre-cat.

You never know, though.

This was my instinct. Especially with the leak in the centre.

But he assured me with a new exhaust it will pass 

Perhaps he ticked the wrong box at test and it did fail on Lambda,whats the printout for emissions look like ?

Yep, always easier if you have the full story.

[dave-b]

My 3.0 elite failed on exactly the same thing back in 2010. A new part system from the cats back secured a pass without any further work. The old system was pin-holed quite badly allowing air to be drawn in, affecting the lamda readings.

[terry paget]

My 3.0 elite failed on exactly the same thing back in 2010. A new part system from the cats back secured a pass without any further work. The old system was pin-holed quite badly allowing air to be drawn in, affecting the lamda readings.

In Germany they use the second Lambda sensors in the facelift Omegas to analyse the exhaust gases in their MOT tests; these second sensors are in the main downpipe after the catalyst and give a good measure of the exhaust gases after catalyst. In the UK we ignore the second lambda sensors, instead we stick a probe up the exhaust pipe and analyse the gas there. That's fine if the exhaust system is air tight from catalyst back; if not, gases can leak out and get sucked in, putting the emerging gases out of spec and causing MOT emissions failure. So a new exhaust system may well cure your MOT emission failure.

[78bex]

I`m probably simplifying this, so if the warning light isn`t on; then all`s good is it not 

[terry paget]

I`m probably simplifying this, so if the warning light isn`t on; then all`s good is it not 

If you mean the engine warning light with a code (420?) referring to emission levels, I suppose so. My son Jonny's 2.2 petrol has that problem and will get a new cat section before its MOT in a month's time.