lambda sensors

[lefty007]

i have a z4 on a 55 plate it has failed mot due to lambda sensor. i had a diagnostic test done and only picked two sensors which were ok. i am now told it has four so how do i know which one is at fault?.

[ph001]

It will be the pre-cat sensors.

[lefty007]

Hanged all sensors and still failing emissions could it be a failed vacuum pipe?

[lefty007]

Had all sensors changed still failing emissions could a failed vacuum pipe be the problem?.

[BumpyZ4]

What are the codes? Are you having any issues with how the engine is running?

[lefty007]

No codes what so ever car drives well but idle not steady

[BumpyZ4]

You need to look at live data with a handheld scanner or INPA to see the Lambda sensor readings and short/long fuel trims. Those reading will point you in the right direction. For instance, if you have a high fuel trim then it is running lean and most likely has a vacuum leak.

[tug]

Sounds like a 2.0 N46. If so could it be a cracked manifold?

[Mike6]

I am confused, a lambda sensor would almost certainly throw a code so if there isn't a code how did it fail on a lamda sensor. If it's a rough idle could it be crack or split in the intake boot
Also does the 2litre have four lamda sensor, thought this would only be on the 6 pot cars.

[tug]

Yes mate, 2 pre cat 2 post cat. Have your manifold checked before spending money. Also you should get a recurring emissions light on the dash, the yellow engine symbol. If not, then your lambda sensors are fine.

Also, try an italian tune up. (thrash the 4rse out of it) take it up to 5000 revs through the gears (obviously not 5 or 6th gear unless you want to )

Also, the N46 is notorious for a rough idle. To cure this you need to have the valvetronic adaptations cleared using ista or inpa software.

[lefty007]

Today I had a smoke test done on car z4e85 came back negative no cracked exhaust manifold and no vacuum pipes. Had emission test done came back over fuelling. Any ideas what this could be?.

[lefty007]

Some one please answer

[tug]

This could be your fuel regulator starting to fail mate. The regulator is situated top right of the engine block, next to the air filter and is kind of rectangular. Mine failed a while back, leading to a lot problems similar to yours. I got one from fleabay off of an E90 which is exactly the same part. Once i replaced this (very easy, one off one on & no coding) the zed went back to normal.

As far as i know the regulator cannot be tested as its solid state (either works or it doesn't) could be wrong though. See if your garage could borrow one to swap to see if this resolves the issue.

Hope this helps.

Cheers, tug

[lefty007]

Thanks tug

[lefty007]

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