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post #1 of 54 (permalink) Old May 2nd, 2007, 08:11 AM Thread Starter
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Emission Light/ o2 sensors/Fault codes & Mots

Hi Guys, as this is quite a talked about topic, I thought I'd try and combine all the info on one thread for you, togetther with all the misconceptions that seem to occur.
EMISSION LIGHT This can come on for a number of reasons, either from a signal from the pre -cat O2 sensor OR the post cat O2 sensor. Often the signal is from the Pre-cat sensor ,and although putting the light on (symbol of an engine ,NOT TO BE CONFUSED with the EML light), usually no fault code will be present. It will remain on for a number of drive cycles (usually 2 or 3 days) even if the the over rich mixture is not detected again within that period. On a modded MCS under load the richer mixture is desirable ,therefore for me I WANT the light on! At idle and gentle cruise there is no richening of the mixture over stock so no MOT worries there. It is under WOT conditions that normally triggers the light. Also using 95 Ron fuel and /or giving it beans whilst still warming up ,will make the light more likely to come on. Remember It is only a 'flag'. Its not reducing power or changing the way the car performs.
Ok as I said earlier, the light can also be triggered from the post cat sensor. This sensor has one job and one job only- To compare the outputs of the 2 sensors to monitor cat efficiency. If it detects that the gasses have not been cleaned up enough by the cat ,the Emission light will be triggered BUT this time you get a code ...usually P0420. This is fairly common with a sports cat, which is freeer flowing (bigger holes) for max performance, but in certain driving conditions may not clean up the gas enough to prevent the light BUT will usually be more than adequate to pass the MOT. -That to most people is the important thing.

O2 SENSORS The car uses 2 pretty bog standard narrow band heated 02 Sensors. And Im guessing 95% of the sensors changed under warranty by BMW , (because a light came on) were actually perfectly OK!
Do you need the sensors atall? The upstream one ,yes definatly. The Downstream one, no you dont! Whether you have a cat or not the sensor is not required either for correct running of the car nor for the MOT. My car hasnt had the second sensor fitted for 3 years!! You need to fit a bung in place of it AND disconnect it (remove from car). Does this make the light come on? No it doesnt. All you get is P0036 code in the ecu. The first sensor and the light work as normal. As the sensors are expensive, you can keep the removed one as a spare for the upstream one
FAULT CODES Always get the dealer to list the codes before he clears them. A fault code doesnt necessarily point to the correct faulty item. An air leak is a classic one. The codes point to faulty TB or Map sensor and its a split in the intercooler bellows.!
MOT (UK) this consists of fast idle and natural idle tests (ie no WOT or the like). HC (hydrocarbons) and CO (carbon monoxide) levels are checked. You do not have to have a cat on the car to pass the MOT even if it has one as standard. Obviously the emissions will be higher and if they are above the limit, you fail and driving the car with excess emissions would be illegal. I'm going to try our new R56 MCS (when it comes) to see if it actually needs a cat to pass the mot /be legal. If it doesnt its coming off for good. Cats do rob power, the more power/boost you run the more the restriction. So no cat is a good thing if you dont 'have' to have it.
Best Regards Roland GTT
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post #2 of 54 (permalink) Old May 2nd, 2007, 09:02 AM
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All very interesting Roland.

I was under the impression that after '97 a car had to be fitted with a cat to pass the MOT, regardless of emissions.

Nice to know you don't need it, although if caught on the road you could still be charged with driving an unroadworthy vehicle right?

It was acceptable in the 80's
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post #3 of 54 (permalink) Old May 2nd, 2007, 09:10 AM Thread Starter
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Hi, its the emission output that determine whether the car is will pass an mot, not the fitting/not fitting of a cat. Most cars will need the cat to be within the emission threshold, though the new R56 MCS with its direct injection ,efficient engine & turbo may?? may get through without. one..... -Can't wait to try it.
Best Regards Roland GTT
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post #4 of 54 (permalink) Old May 2nd, 2007, 09:14 AM
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Arrow MOT / Emissions / No CAT

That is very interesting, and clear.

I'm due for my MOT in November for my GTT260 supercharged car. I'll be coming to Dorset for that , and I would like to see what emissions are being released with a straight through pipe, even if they are too high, but still out of pure necessity to feed curiosity.

I'm still totally amazed at the very VERY low emissions seen on the new 300bhp Turbo.

Cheers,
K.


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post #5 of 54 (permalink) Old May 2nd, 2007, 09:25 AM
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Hi there Roland,

My emmisions light is on and has been since my performance Manifold was put on. Although the car seems to be running perfectly normaly the light is still on but, its happend twice now where i will notice the emmisions light has gone off on its own, but then will re illuminate after a day or so, why would it be doing this?

Also after i fitted an enlarged throttle body it revs up and down on tick over, would this put the emmisions light on?

Oh and its a Mini One i drive.

Best Regards

Alex

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post #6 of 54 (permalink) Old May 2nd, 2007, 09:35 AM
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Dude, read it again

"EMISSION LIGHT This can come on for a number of reasons, either from a signal from the pre -cat O2 sensor OR the post cat O2 sensor."

Your sensors are not reading OEM typical values due to a free flowing manifold, hence your Emissions Light is lit. The fact it goes out after a few drive cylces proves nothing is actually faulty and that you have probably exceeded a threshold in emissions for a split second or two.

Cheers,
K.


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post #7 of 54 (permalink) Old May 2nd, 2007, 09:53 AM Thread Starter
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Hi, yes if it goes out its almost certainly a signal from the pre cat sensor ,with no code.
Enlarged Thottle body shouldnt cause any additional fluctuation at idle.
Best Regards Roland GTT
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post #8 of 54 (permalink) Old May 3rd, 2007, 07:06 AM
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no orange light on gtt220 until i added bigger intercooler, ok for a few weeks then added gtt snoot boots, pretty soon after that got my 1st emissions light up
now almost a weekly occurrence, logic suggests that more cooler/denser air would lead to a leaner mix? is my ecu over compensating,
i think i can smell fuel when car comes out of garage in morning, never noticed before, also seem to be getting less mpg [ that also could be down to new 215/40/17 rubber]
or have i got the wrong end of the stick here, i appreciate that the light is a good thing, but dont feel i am driving the car any harder than pre intercooler mod, would a re-flash or new map help?

wonders out loud if jcw injectors would help prevent orange light, by more efficient fuel delivery
or am i barking up wrong tree here as well?

carefree
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post #9 of 54 (permalink) Old May 3rd, 2007, 07:21 AM
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...you could have an air leak in your snoot boots if you fitted them incorrectly.


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post #10 of 54 (permalink) Old May 3rd, 2007, 08:31 AM
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Quote:
Originally Posted by GTT 260 View Post
...you could have an air leak in your snoot boots if you fitted them incorrectly.
I was just thinking the same.

It was acceptable in the 80's
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post #11 of 54 (permalink) Old May 7th, 2007, 08:47 AM
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double checked boots, tight as a ducks, boost is good, i know what happens with loose boots
and its not good, thats why i bought the gtt ones, any other ideas?

carefree
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post #12 of 54 (permalink) Old May 7th, 2007, 10:54 AM
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Correct checking...

Quote:
Originally Posted by alski View Post
double checked boots, tight as a ducks, boost is good, i know what happens with loose boots
and its not good, thats why i bought the gtt ones, any other ideas?
How did you check them - just visually?

Cheers,
K.


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post #13 of 54 (permalink) Old May 7th, 2007, 11:32 AM
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visual and wet digit, not sure if i would feel any breeze, but don't smoke,
clamps look tight, square, evenly spaced etc
and my dials show between 4 and 5 bar most of the time
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post #14 of 54 (permalink) Old May 7th, 2007, 11:34 AM
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Roland, if my pre cat sencer is b**g**d, can i take it out and clean it or do i have to get a new one? If so how much are they if you know?

Alex

(i tryd claiming from tesco coz i only use their 99 octain fuel, and i have all the proof of purchaces slips but they still havnt done anything about sortign my car out, if its cheep enough i may just get on with the repair myself.

Alex

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post #15 of 54 (permalink) Old May 7th, 2007, 04:48 PM
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WHat about the when a modded Mini S is given a good thrashing & both the emmisions light & traction light come on? DOes that mean your ASC/DSC are now switched off
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