Hi people looking for a bit of guidance on this one please.

This Z3 has failed its MOT on high emissions being to high. Forgot to bring the fail sheet home so cant remember the reading but on our machine they were all over the place CO 0.4/2.5 Hc 50/400.

Bit of history of the vehicle, it has been parked up for about 3/4 years now because the owner had a child, but last week we were asked to fetch it and carry out a service and mot so they can use it again. Service went ok we did all the usual oil filter, air filter, fuel filter, plugs and an oil flush then off for mot to have it fail only on emissions. Spoke to the customer and they have informed me there has been a bit of history with emissions with this vehicle in the past. They told me that it had a cat in 06 for mot and new MAF sensor in 07 all to get it through emissions. Every time it still didn't go through without the mot station revving it flat out for ages according to the customer. I know its been a few years now since cat and MAF sensor were fitted but up to now its only done 60k miles and was only used in the summer till it was taken off the road in 2009 so I cant see these being the fault (but I know it could still be). I have spoke to the customer and said that I could stick a cat on it and it would probably pass but next year we would be in the same boat again, so its time to fix the fault and not the affects of the fault.

This is what I have checked so far .....

The only Fault codes were for Cam sensor and O2 sensor. Scoped the cam sensor and found no trace so fitted a new cam sensor and now ok, but the O2 sensor I think was me but when talking to the customer he was convinced this was the fault because he had read it on the internet and told me to try it, so I fitted a new Bosch one (the old one didn't look that old and that was also a bosch one).

Fuel pressure is at 40psi running with the vaccuum disconnected and 35psi with it connected. The injectors are switching at 2.8ms.

Smoked the inlet to only find 1 tiny tiny leak from the DISA valve. That's now fixed. I have also disconnected and blanked the rocker to inlet pipe which made no difference.

Compression test all about 180psi (AD says 145/160) Is that too high???? Also I have done a cylinder leakage test all ok and about the same.

MAF sensor 0.8v on tick over and 4.2v WOT. So that should be ok

ECT 70c-1v 80c-0.9v. No drop outs. AD does say 80c should be 0.8v.

Powers and grounds to the ecu all ok KOEO and KOER.

O2 sensor - this is where I'm stuck when I scope the sensor it switches between 1.7v and 0.8v and the earth is at 0.75v. Is this a "floating earth" or a bad earth. Because on live data it reads 0.1v and 0.8v. If I earth the sensor out the emissions go off the scale and I get a code for O2 sensor ground to earth so I'm thinking the 0.75v is right and its a floating earth but I dont know.

Many thanks and I hope this reads ok and makes sense.

Andrew