Help - Emissions!

I took the 'F for it's MOT this morning and it failed on emissions. I am now at a loss as to what to do next so could really do with some advice to get this car on the road!

I've already done quite a bit to the car as last time the tester couldn't even get a reading because it was so off the scale. This time the readings were:-

CO % VOL: should be 0.30, actual 4.79
HC ppm VOL: should be 200, actual 205
Lambda: should be 0.95 to 1.09, actual 0.88

Second go:

CO % VOL: should be 0.30, actual 4.87
HC ppm VOL: should be 200, actual 258
Lambda: should be 0.95 to 1.09, actual 0.88


I've already replaced the lambda sensor with a new bosch unit, new cat, rear box, fitted a standard airbox and filter and checked the vacuum hose into the ECU.

The car runs beautifully, idles as it should, temperature is rock solid, no apparent head gasket issues, no smoke when warmed up, and it goes like a rocket.

You can smell that its running rich though.

So, what do people think? As I said, I'm at a loss what to do next?

Thanks in advance...

Not an expert on ECU etc, but from a chemistry point if view the high monoxide reading is indicative of incomplete combustion. The hydrocarbon is not too far out, which I would take as not too serious over richness, unless there is physically too much fuel for the available oxygen to efficiently combine with.
I may be falling into the trap of applying science to the MG, which regularly defies the laws of physics Cap'n!

Sorry not much help......just thinking aloud.
One of the sensor gurus will be along soon with some more helpful advice.

Some good points there John.

What your saying could be indicative of the timing being out. It had new belts not long before I got it as well...

Steve could your cat have collapsed during the fitting of new exhaust bits?

Paul, It shouldn't have as it was all fitted at the same time. I also know that the old, knackered cat rattled because the matrix was in bits. No sign of that now.

stevecrx wrote: Some good points there John.

What your saying could be indicative of the timing being out. It had new belts not long before I got it as well...

A good point, though you say that it ticks over well. Not sure how tolerant the K is to timing etc being out: too many teeth out would result in internal mechanical distress!

That's what stumped me - saying that it runs well and goes like a rocket. Timing can't be out.:shrug:

My first thought looking at that very high Co was Engine temp sensor.

Running rich as it is I would not expect it to go like a rocket.:nonod: So maybe only running rich at low revs, which again points to the engine temp sensor as if the ecu thinks the engine is cold it will inject more fuel.

Well, I have only ever driven mine and so have nothing to compare it to but it feels to me as it should.

Temp sensor seems like a starting point. Might go and see what its putting out with the multimeter.

It's the green one under the manifold isn't it?

Could it be that with the weather out side being very cold that it has cooled down to much and giving false readings with a cold engine, I would take it for a run of 20 miles to get it hot and clean everything out then ask them to do another reading on it.

Well it was snowing when I bled the coolant system and brakes earlier so I guess it is quite cold. :lol:

I did have it idling for 45 minutes to check for air in the system and the mot place is about 8 miles away so I should have warmed it up properly.

Just looked through the emissions sheet again and I missed this:-

Natural Idle Test
CO % VOL: should be 0.50, actual 0.90.

Not so bad at idle. Hmmm

Does it have a after market ss exhaust or a standard one as there was talk a while ago about having to cover one of the exhaust out lets to get the emissions down maybe David can post the thread