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My MOT has, previously, been a sweat-free experience. Today, however, I failed the Lambda emissions....it was hovering at around 1.35 (1.30 is the pass mark).

On the retest, thanks to a change of tune & a tolerant tester who kept the machine cycling, it crept in at 1.29 - still not good.

Any ideas re causes? I have considered a gradually dying o2 sensor (but which!?). I'm throwing no codes. Also initially I was using the factory tune with a CAI (if that could affect it?), and I'd plated over my cut-out holes (though I suppose one may have an air gap - fairly sure I nipped them up though).
 

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Air Leak, CAT, Lambada Sensor, EGR Problem, MAF Sensor, Air Leak after MAF and not being detected as MAF or even an MOT testers machine out of calibration.

Exhaust should be easy to prove by the rag up the exhaust trick.

If you like me you would prefer it to be perfect, but, I would just run with it personally and see what its like next year.

I assume the Cold Air Intake could affect it, but don,t really know (Cold Air, More Volume, Weak mixture that may not be possible to be tuned out by the system ?).

Maybe the Oil on the CAI filter has fouled the MAF sensor ? Worth a clean ?
Even a MAP sensor giving a wrong reading can do it.



Jack
 

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Discussion Starter #3
Air Leak, CAT, Lambada Sensor, EGR Problem, MAF Sensor, Air Leak after MAF and not being detected as MAF or even an MOT testers machine out of calibration.

Exhaust should be easy to prove by the rag up the exhaust trick.

If you like me you would prefer it to be perfect, but, I would just run with it personally and see what its like next year.

I assume the Cold Air Intake could affect it, but don,t really know (Cold Air, More Volume, Weak mixture that may not be possible to be tuned out by the system ?).

Maybe the Oil on the CAI filter has fouled the MAF sensor ? Worth a clean ?

Jack

Lambada sensor? I have no rhythm!
 

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If there was a problem with the O2 sensors, it would throw a solid code, so I reckon both banks of O2's are fine.

Instead inspect the MAF. If you have a wet type air filter especially if it had been DIY cleaned, your MAF is probably contaminated. You could spray clean it and to help out return back to stock tune to get you through. Take care not to touch the MAF, its delicate.

Check all ducts are secure & clamped and although not too important, position the open ends of the MAF facing the flow of air :yup:
 

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Discussion Starter #6
Gents...these cars dont have a MAF, they have an Intake Air Temperature sensor on the intake pipe, so that idea bites the dust.

I've also just noticed that my MPG has dropped by 3-4 recently, previously its been rock solid (EVIC readings), so, given the LAMBDA, I'm a bit confused as the reading is too high, which I think means its too lean? ....if my fuel economy is worse, surely I should be running richer?

Could running a CAI with 95 RON instead of the tuned-for 97-99 RON be a cause, given that I've noticed I get better MPG off the better stuff?


More quiz questions may follow!
 

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Yes you prompted me to check mine, it has 2 wires going to it so its not a complete MAF unit as a MAF unit has about 5 wires, 2 of which belongs to the IAT. In our case we only have the thermistor part or referred to as IAT.

If either O2 or IAT were at fault, it would pop a code unless not picked up by vehicle or your scanner?

If you got a multimeter handy, you can check for voltage output from the thermistor. If its a good'en it will feed an output a little under 5 volts or more around 4.7 volts. As you blow warm air, this voltage will slowly drop down. If you see no change, then you need to renew it. Again, it would have popped up as a code, so I doubt you have a fault there.

Also try a battery disconnection/fuse 11, to see if it made a difference, check the connections to the O2 sensor plugs, a revised johan tune or improvement to MPG

Please keep updating :yup:
 

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It may be worth while checking the Intake Air Pressure Sensor (Barometric Pressure).
This basically changes the fuel/air ratio settings to compensate for running at different altitudes. The Intake Air Pressure Sensor should be a bout 14.7 psia (about 100kpa) at sea level.

Also: If the Intake Air Pressure Sensor is mounted in the intake ducting after the CAI filter this could affect the air flow past it and give a false ptessure reading. i.e. The Intake Air Pressure sensor is there solely to compensate for running at different altitudes and the pressure should be totally stable and only change as the altitude changes. If the sensor is in a flow of air, the pressure on the sensor will give a false reading and will no longer measure the actual barometric pressure. It may be that if you run with a CAI filter a better location may be needed for the Intake Air Pressure sensor so that its not affected when the engines running or the cars moving.

On cars that don't have a MAF meter (Yours: Lol) the Manifold Absolute Pressure is used to estimate the actual air flow by the PCM measuring MAP, IAT, and Throttle Body position so if the MAP sensor gives a wrong output the fuel/air ratio could be also set wrong by the PCM.

EDIT:
Only talking principles above. From my previous post it should be obvious I don't know your particular car.
Yours may not even have a seperate Barometeric Presure sensor. It may get the barometric pressure from the MAP sensor.
:bsflag:

Jack.
 

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Discussion Starter #9
as an experiment I accelerated up a 1 in 4 hill.....and got a loud buzzing/exhaust/vibe noise from the front end. Given the other symptoms I'm starting to think I may have an exhaust manifold (header) stud / gasket issue, or a bad seal on the cat pipe - comments?
 

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That sounds like a problem, did you impact your cutouts on a road hump since the last MOT? Possibly the header nuts may have become loose, hopefully hasn't caused some hidden damage further up?

When the engine is cold, worth checking both banks and the connections at the CAT's & re-torque them up as you go. Keep it posted :yup:
 

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I thought you had cut-outs??? could be them leaking,cos a reading of what you have is normally a leak in the exhaust system sucking air back in
 

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Discussion Starter #12
I thought you had cut-outs??? could be them leaking,cos a reading of what you have is normally a leak in the exhaust system sucking air back in
they were both removed & sealed with blanking plates....so I guess I need to follow the full length for holes / loose flanges / blowing gaskets or a bum manifold. Given the grumbly vibe / noise under load, I suspect the latter. I dont think theres anything obvious or the tester would have noticed
 

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I've just realised,you must have had your car repaired from the crash.....that was quick
 

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I was at the same repairers last Thursday and KB had already taken it back then.
 

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Discussion Starter #15
nope....it finally went in today (Easter closure at the body shop), estimated return date is 6th May. I have been given a 63 plate (2300 miles) BMW 530D M Sport to slum in until I get mine back. The MOT was a headache....I knew it was going for repair...if it'd failed the test it would have gone in with the remainder of its old MOT (because I wouldnt have had time to repair it), & come out without one!
 

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Post some after photos of the repair if you can.
 

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They told me it had been and gone....

Never trust a second hand car salesman...
 

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Discussion Starter #18
the new car is very sterile. Its reasonably prompt, comfortable etc.....but its definitely 'just transport'
 

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the new car is very sterile. Its reasonably prompt, comfortable etc.....but its definitely 'just transport'
Most are. They all "work" if you know what I mean but very few cars have any character
 
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