mot fail today on emissions, anybody on here able to give me any suggestions for possible causes etc
The car is turbod, trd panel filter and put wynns clean burn in the fuel but still no joy.

Sports cat?  They need to get pretty hot to work properly.

That was our thought so after the 1st failed test I took it on the motorway for a spin but still failed.

O2 reading is high, maybe a leak on the manifold

Ideally find a "more helpful" mot tester who maybe able to over look the problem  s;) s;)

Quote from: "rbuckingham"O2 reading is high, maybe a leak on the manifold

It also is making a rasping noise, very much like the heat shield rattle, but theres no heatshields s could it be manifold gasket ?

Quote from: "s12vea"Ideally find a "more helpful" mot tester who maybe able to over look the problem  s;) s;)

ha he was a good bloke to be fair, gave me 3 separate attempts at it, the 3rd one after a blast down the m42

Also was pointed out to me that id only done around 1000 miles since last mot, maybe needs some help like cataclean to aid cat efficiency. Any one tried this?
I have some readings from o2 sensors too,what should they be operating at as mine fluctuate wildly.

I've got a 200 Cel sports cat and it caused no problems at my last MOT.
Do a few more miles than you though.

I've had no end of trouble with exhaust manifold and turbo gaskets sucking in air and causing fueling issues.  Mine had a tiny leak between the turbo and manifold which over time caused the long term fuel trims to adjust incorrectly.   Disconnecting the battery resets the fuel trims until they have been relearnt.  The only way to fix it permantly is the fix the exhaust leak then reset the fuel trims.

Fuel trims if anyone can decipher them for me, car was at 3000 rpm

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Well it needs sorting one way or another   s:evil: :evil: s:evil:  ive just tightened the manifold to engine, but as ive no mot I cant get out and test it.

Been doing some amateur sleuthing on this and it looks quite odd. First fast idle suggests a lean mixture (lambda >1), but the second suggest it is rich (high CO)!

You say you had 3 tests, we're the results all consistent with the above in terms of how it failed?

Quote from: "lamcote"Been doing some amateur sleuthing on this and it looks quite odd. First fast idle suggests a lean mixture (lambda >1), but the second suggest it is rich (high CO)!

You say you had 3 tests, we're the results all consistent with the above in terms of how it failed?

Yep all the same, the tester thought it was odd too.

It's the long term fuel trims you need to look at.

Quote from: "Davegtst"It's the long term fuel trims you need to look at.

There you go. They are idling at 1200 then rev to 2500 rpm.

Quote from: "wotugonado"

Quote from: "rbuckingham"O2 reading is high, maybe a leak on the manifold

It also is making a rasping noise, very much like the heat shield rattle, but theres no heatshields s could it be manifold gasket ?

Quote from: "s12vea"Ideally find a "more helpful" mot tester who maybe able to over look the problem  s;) s;)

ha he was a good bloke to be fair, gave me 3 separate attempts at it, the 3rd one after a blast down the m42

Also was pointed out to me that id only done around 1000 miles since last mot, maybe needs some help like cataclean to aid cat efficiency. Any one tried this?
I have some readings from o2 sensors too,what should they be operating at as mine fluctuate wildly.

I would say it's leaking then, most likely at the turbo, that where my leak was.

One point I have realised in my research is that fuel trims and emissions tests are affected by very different things even though at first glance I didn't realise it:

Fuel trims are influenced only by the car's O2 sensors which are before the cat, there are no CO sensors or HC sensors for the engine to react to and the exhaust gasses haven't been through the cat.

The emissions test is looking at all these things, and after cat treatment,  so I wonder how relevant fuel trims are to helping find emissions problems detected in the mot?

The odd thing for me is the fact that it is both lean and rich in consecutive tests. A leak after the O2 sensors and or cat would certainly give a lean reading for the mot test without affecting fuel trims but wouldn't explain the failure for high CO which is a rich issue (I assume).

Thanks for that lamcote.
ive a feeling its an accumulation of things. So im going to do an oil change, run some cataclean through, work my way along the intake checking for leaks.Im going to heat wrap the cat to help get it warmer quicker And change the turbo manifold gasket as its all 2nd hand I cant say if its any good or not. I will also check the 3 amigos and the donut rings as I remember me and my mechanic having fun doing those up. Also after some researching on dual exit exhausts when the probe is put in the one exit block the other up with a damp cloth,
as according to another forum it contributed towards giving a false reading.
All that within the next 10 days .........

Can anybody give me an idea if those fuel trim readings are normal ?

I'm not sure there is an answer to that. The fuel trims are simply adjustments made to whatever Base map the engine is running, based on the readings taken from the O2 sensors.  I assume your engine management runs in closed loop using the O2 sensors to initiate the fuel trims but I believe this can be switched off by whoever mapped the engine. There are lots of YouTube videos which explain all this but as I say fuel trims may not help. I have certainly seen comments about people getting false lean results from testers using the equipment wrongly and getting air trapped in the exhaust pipe next to the probe so air might be getting into your exhaust system via the second outlet, this may explain how you are getting the both lean and rich fails,  which otherwise seems unusual.

I will continue with my web searching and report back if anything looks helpful.

Edit, having said that there is no answer, it seems that fuel trims at less than 10% are pretty normal and suggest the car is not trying to massively compensate for something. Levels of 25% seem to be a typical maximum.

What management system are you using and have you had it mapped on a rolling road?

This is quite a good read which supports what has already been said.

 m http://www.obd-codes.com/faq/fuel-trims.php m

Cheers guys for the help, good link mrzwei thanks.
Its a tte turbo so it has a chip that you cant alter.

Having thought about it a bit more there's more logic to it than I realised,  I told you I am an amateur.....

The first run shows the mixture is too lean (lambda 1.2) and the CO is a pass. In the second test the mixture has got richer (lambda has decreased) and this has caused the CO to increase and fail (too rich). That would actually seem entirely logical. This presumably means that at any given point the engine is running rich relative to the exhaust measurements. That may be supported by the fact that the long term fuel trims all seem to be negative ie taking fuel away to make the mixture more lean.

That suggests that the exhaust has too much air relative to the mixture so the leak theory looks plausible.

Hope my ramblings are not too confusing...

No keep em coming   s:D s:D  i was already confused.
Think I may have an o2 sensor operating slightly out of maximum range too, not much so i dont know if it woud cause an issue.

I suppose having clean and properly functioning MAF and O2 sensors is essential to pass any MOT.

What makes you think the O2 sensor is out of range?

I think operating range should 0.2 to 0.8 volts  mine is sometimes closer to 0 and maximum 0.96
dont know if this is enough to be an issue though.

MR2.com says:

Testing O2 sensors on the workbench.

Use a high impedence DC voltmeter as above. Clamp the sensor in a vice, or use a plier or vice-grip to hold it. Clamp your negative voltmeter lead to the case, and the positive to the output wire. Use a propane torch set to high and the inner blue flame tip to heat the fluted or perforated area of the sensor. You should see a DC voltage of at least 0.6 within 20 seconds. If not, most likely cause is open circuit internally or lead fouling. If OK so far, remove from flame. You should see a drop to under 0.1 volt within 4 seconds. If not likely silicone fouled. If still OK, heat for two full minutes and watch for drops in voltage. Sometimes, the internal connections will open up under heat. This is the same a loose wire and is a failure. If the sensor is OK at this point, and will switch from high to low quickly as you move the flame, the sensor is good. Bear in mind that good or bad is relative, with port fuel injection needing faster information than carbureted systems. ANY O2 sensor that will generate 0.9 volts or more when heated, show 0.1 volts or less within one second of flame removal, AND pass the two minute heat test is good regardless of age.

Interestingly in the same article it also says if the car thinks the O2 sensor is faulty it will not switch to closed loop operation and will therefore run rich in open loop on the Base map, but wouldn't you get an error code if an O2 sensor was not working properly?

Interesting. Yeah if it was a complete duffer it would give a code. But reading up it maybe just sluggish and may not throw a code.
So im gonna swap them round and see if the readings follow the 02 sensor. Cheers for all the info, appreciate it   s:D s:D