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Iva Emissions


Guest mcramsay

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Guest mcramsay

I have an exhaust running down either side of my marlin, on iva when checking the emissions will they check both sides and average the results or only probe one exhaust bank?

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Guest mcramsay

So the car had an mot today to check emissions before iva. Both exhaust banks give similar readings and both failed on high co & lambda on the fast idle test I think the co was around 0.7%. Marlin think the cats are not man enough they were 200cpi specials off eBay. No fault codes or anything when I scanned the ecu last week. So high lambda & high co are a bit of a different combination... any thoughts?

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Odd combination. Carbon monoxide is a product of incomplete combustion, too much fuel or too little oxygen. No other source for the CO. There's effectively none in the air and nowhere else it can come from. So there is incomplete combustion going on (Fact) to produce a rise in CO emissions. ( You want them below 0.3 probably.) The CO reading is the boss reading here as it's almost impossible to have a false reading, apart from faulty measuring equipment. (Unlikely as all cars having MoT's at the garage would fail.)

A lambda sensor is really an oxygen sensor. Should be between engine and cat and if reading high is signalling unused oxygen present at the lambda sensor. So the ECU is being told excess oxygen present in exhaust gas, interpret this as being due to lean mixture so take action to increase fueling.

How to get excess oxygen at the lambda tip? If it's not a missfireing cylinder or two (one for each side? Unlikely) allowing unused oxygen through then oxygen (in fresh air) must be getting in to the exhaust. Favourite would be exhaust leak allowing oxygen to be drawn in upstream of the lambda. So points to leak at manifold-face gasket/exhaust joins/collectors.

 

Would be nice to know CO2 and HC figures. I would expect high HC and lowish CO2.

 

I wouldn't suspect brand new cats, even free flowing ones and IMO they are unlikely to reduce 0.7 CO below 0.3 in any case, even if you fitted more efficient ones.

 

I take it you are using a closed loop narrow band lambda? If you are not and are using after market ECU and no lambda then the above still applies. Running rich but with exhaust leaks. I think! :unsure:

 

Nigel

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Guest mcramsay

I agree that the combination of results are conflicting, and I think I have two issues. I'm taking my laptop over to Marlin tomorrow as I can see all the live data on the engine. If the lambda reading is spot on when reading from the ecu sensors then air must be getting into the exhaust after the lambda. I should be able to see from the short term trims what the ecu is having to do.

 

There def are no missfires as I would have a fault code on the misfiring cylinder. And the fact they both exhausts are giving the same issues when they run in 2 banks of 3 makes me think there is an air issue on the inlet. Possibly my air filter is too restrictive and the engine cannot get enough air and this has a richer mixture giving higher CO? Will do some testing tomorrow

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Inlet air leak will confuse the ECU as not all intake air is being metered, resulting in the ECU getting confused by the lambda reading. High lambda will make the ECU increase fueling and it may learn that from prolonged idle and this would result in raised CO levels. The proportion of unmetered to metered inlet air may/probably would vary at different revs and confuse the ECU even more. I don't think it will be air on the inlet side. High CO means an over-rich burn. Period.

What the ECU is reading (excess oxygen) it is failing to correct by richening the mixture. I still think air is entering the exhausts after the cylinder head.

Fascinated to hear what you discover tomorrow.

 

Nigel

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  • 4 weeks later...
Guest mcramsay

So just an update, new exhaust has been fitted to the car with the cat in the correct place, emissions were spot on and will fly through the IVA retest. Test is booked for next Friday so it looks like a guaranteed pass!

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Guest mcramsay

The cats were not getting warm enough to light off. The symptoms were higher than normal co & hc but lambda was correct. and the emission results were pretty much exactly what you would expect if not running cats. I completely overlooked the need for heat when making the exhaust. Other than that there were no running faults on the engine/ecu which to be honest is great news as it had been a really difficult transplant. BMW engines do not like being plucked out and put in another car, especially if you start taking parts off like the fuel evap system, secondary air pump and modifications on the inlet manifold! All these systems feed back to the ecu which then throws a wobbly when it can no longer detect them!

 

Bring on the retest! I might get one dry morning to get the car out on the road for my first drive before xmas!!

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