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Frankp2112

Emissions Issue

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Hi,

Unfortunately just failed the MOT on emissions specifically the Lambda readings all a tiny bit high.

The tester suggested a pin hole leak in the exhaust could cause it but could not find anything obvious.

Any suggestions on trouble shooting would be gratefully received.

Thanks

Frank

 

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Did you take the car for a good old blast before the MOT? The cats need to be red hot before the MOT and I always ask the tester to do emissions first. 

Maybe some redex? 

I've read about people covering the exhaust with tissues or a cloth to get the emissions low. 

Or get a friendly tester 😂

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2 hours ago, usman10316 said:

Did you take the car for a good old blast before the MOT? The cats need to be red hot before the MOT and I always ask the tester to do emissions first. 

Maybe some redex? 

I've read about people covering the exhaust with tissues or a cloth to get the emissions low. 

Or get a friendly tester 😂

It’s a lambda failure not a CO problem so it’s a leak or a lambda sensor problem. 
 

Mark

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Hi

stuck a load of redex in it and when for a 30 mile blast.

Its just the Lambda thats high - could it be a tiny leak somewhere?

 

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I would suggest reading the live data off the DME to check the HEGO sensors are moving through the voltage ranges correctly (if one side is reading 0V or is fixed, then there is a problem with the sensor). As our cars are fitted with narrowband, they should oscillate between rich/lean continuously. If it's a RoW car then there is a single sensor per bank. It is also worth checking the fuel trims to see if the car is enrichening or leaning out on a particular bank, this may help to scope the problem if the issue is pre O2 sensor

This can be done with a basic handheld scanner and does not require durametric etc

Most likely cause for high lambda is a leak in the exhaust system, anything intake should be picked up by the vehicles HEGO sensors and corrected when running in Closed loop control (ie steady state and idle) assuming they are operating correctly and that the leak isn't so big the DME can't correct any further. I'm sure you'd notice running/driveability issues if this was the case.

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My Cayman had similar. After changing the exhaust it passed emissions and has been fine ever since. 

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Have you checked the clamps where the C bends join the back box on each side. Mine were very rotten and causing a small leak.

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Hi,

Thanks for the suggestions - clamps are new last year - the MOT tester said he could not see any obvious leak.

Will check the sensors - may cars has 4 sensors 2 on each side.

If I need to get a new back box any suggestions that don't sound terrible.

Thanks

Frank

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Hi,

I have checked the codes and they are all OK

I have found a really small leak from one of the sleeves that joins the elbow - I have used orginal Porsche parts here - what is the best way to join the sleeve I have used quite a lot of exhaust paste.

Any advice welcome

Frank

 

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If the sleeve makes no difference, have a look at your oxygen sensors.  Had two come loose on the 986 when I had that which resulted in a high reading. 

A dab of loctite and tightened them up and readings were much lower.

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Have the same issue, it's borderline fail. The garage is kind enough to keep testing it until it's in the pass range, but I've recently discovered that the backbox may be blowing on the seals.

Was also told that bad O2 sensors (pre-cat, nearest the engine, not the rear bumper) can also be the culprit. I had a failed AOS which coated the sensors in oil and this, mixed with a blowing back box, is most likely definitely the cause.

You can get a garage to weld your sleeves so that it solves the blow. Legally you're allowed to drive a car with a failed MOT to and from a garage for repairs for said MOT.

So yeah, I mirror what everyone else is saying. Fix/weld the sleeves, and if not, change the pre-cat sensors!

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