Help failed MOT

[J@mes]

I had a split in the exhaust manifold on my M3. It draws air in through the split, so the exhaust gases passing the lambda are 'diluted' compared to what is actually leaving the combustion chamber. The lambda reads this as running lean, and so dumps more fuel in to compensate. So now, the mixture is too rich, not all the fuel is burnt and it gets dumped straight down the tube. Sadly when an MOT man is at the other end, its leads to glum faces all round.

oh right!

i would have thought a split exhaust would make the exhaust gases escape out of the split (and thus not allow any outside air to come in, and if outside air did come in i would have thought that would make the exhaust gases "cleaner" so to speak lol.. i guess it depends where the split is re the lambda probes too!)



but obviously not! lol

 

[Reg]

You're basically right James - the air going in does make the gasses cleaner (i.e. more dilute) inbetween the split and leaving the exhaust. Sadly, the lambda reads that as 'too lean' and chucks more fuel in.

A bit of gas will escape, hence why you can often smell petrol inside the car. Its all to do with pulses. I couldn't really hear a difference when the split first happened, it got gradually worse. First was the already bad mpg getting worse, then I could smell it, then when I really listened for it I could hear a sort of woofling noise.

If the split had been after the lambda, it wouldn't have been a problem.

 

[CUPRACAR]

I took the car to Awesome this morning and they carried out numerous tests to establish the reason for the high emissions, the stage 2 map was fine with no over fuelling issues, MAF and sensors OK.
Awesome’s diagnosis, fooked cat. Many thanks to Dean who kindly rang Blue Flame trying to get them to change it FOC, but they said the best they could do was to give me trade discount.
On arrival at BF they still claimed that they have never had a failure on the 100-cell cat and the problem was probably over fuelling. I told them to change it anyway. After removing the cat the fitter brought it to reception and said in his opinion there was nothing wrong the cat, suspected my map was at fault, at this point I noticed that the cat was 200-cell, not the 100-cell I requested. Told him to fit a new 100-cell and I would get Awesome to check the emissions again.
Back at Awesome everything checked out fine.
Sailed through the MOT, retest emissions super low at 0.01%.
I had this system fitted at BF 13 months ago and it threw up fault codes within 2 days after fitting, I got used to cancelling it every week, so it looks like its been fooked all the time.
Thanks to everyone for your help and yes Mark, your diagnosis was spot on.
BF said they would send the cat back to the manufactures and if it was a manufacturing fault I will get a refund, lets hope they do.

 

[J@mes]

that is bad that they fitted a 200cell cat to ur car when u requested a 100 cell!

makes me think!...


glad u got it sorted tho m8!


edit: how much did u have to pay out in total because of BF **** up? (including extra costs from Awesomes, plus fuel to BF and back!) id be tempted to call trading standards is nigel doesnt cough up!

 

[m0rk]

Thanks to everyone for your help and yes Mark, your diagnosis was spot on.

I became a bit of an expert on emissions and how to get it right when my 1.4 was unable to pass emissions 6 fails........ then it failled on something else lol

 

[J@mes]

I became a bit of an expert on emissions and how to get it right when my 1.4 was unable to pass emissions 6 fails........ then it failled on something else lol

we only learn the hard way!