Error code P0420 'frustrated'

MickG

Member
Bought the Z4 (07 2L Msport 33k) earlier this year and to be honest its getting me down to the point that it maybe wasn't a good buy or goodby! So you say what's happen:- runflat tyres in the bin, replace with normal rubber, that's better, acquired a space saver spare for the boot (from my friendly car breaker £20 including jack etc) all feeling good. As I wanted cruise control for my Italian trip I bought the parts from Spopers Lincoln and fitted it myself with the aid of the Forum, ' I did put the wire in the wrong terminal rail stupid boy! and caused the fan to run and it would start!!
My first fuel filled up; drove one mile; first set of lights at tickover the engine started to 'shake' Esso fuel?? doggy fuel? then a day later the engine management light came on, my friend read the error code and the description was ' lower efficiency cat bank 1' so, changed one of the manifold sensors (£70) and my son with his equipment checked out the fuel mixture and found it was going from 14.5 up to 17:1, so he suggested the mass air flow meter so we changed that (£35 Bosch one) with the light turn off next week it returned same code. Bought second hand injectors (£50) no different; same with the air flow meter. As my son is WGMotorworks and one of his colleges who works in a BMW garage West London said every car that comes in we have to change the pencil coils! £77 later fitted a new set of Bosch coils, down the road and on comes the light again, maybe it is the Manifold (£740+vat) After 4 months I managed to buy a second hand one. Ho Ho ho I missed out the ABS motor light on the dash. We bought the car to have a trip to Italy in June and basically drove there and back with the dash board looking like a Christmas tree. The ABS unit from the steelers was £1780+vat and that didn't include reprogramming it, fortunately I found BBA Reman in Rochester who replaced the abs motor for 194+vat in less than 24 hours!
With the newish manifold fitted (the one on the car had been changed before!??) the car appeared to run for two weeks without any problems and tickover was slightly better, yep you guessed it; Sunday night cruise control on at 65mph the light is on again same error code!
What do I do with it? dare I take it to a BMW garage? or ? any help would be appreciated.

Mick G PS My 158k Vectra estate has never gone wrong!
 
Blimey Mick, you've had your fair share of aggro with that one. I'm sorry I cant help, I had the ABS go on mine and eventually got it sorted, Just general crap build quality I'm afraid from a once respected marque.

Good luck with it.
 
That's bad news Mick.

It looks like you've thrown a lot of parts at the car, but these engines (old N42 and newer N46) experienced quite a few issues which affected the way the engine felt and caused the emissions light to come on. Often people would do the obvious bits like coil packs and intake parts and find it made no difference. I was one of these people a few years back.

Most common with the older engines was the tendency for the upper chain guard to snap which caused rough running and sometimes timing issues. The quick fix was to fit an upgraded chain tensioner (cheap and easy) which often helped. These engines also use a vacuum pump at the back of the block which can leak and cause the same issues you describe. The vacuum pump is easy enough to access and is worth looking at.

I expect you'll find you have some sort of leak somewhere. Whipping off the rocker cover gasket will reveal the upper chain guard and you can check the chain tension to see if that needs looking at.
 
Stratts thanks.

Yep there is a minor oil leak from the vacuum pump (not that I knew it was a pump) at the back of the head/block, and yes; next on the list but would that cause the error code? My son feels its more to do with the fuel system hence the mixture going wayward now and again, unfortunately its not Vauxhall if so it would have been remapped and sorted by now! the Boy has achieved 400bhp + out of several customer 2 litre Astra and Corsa's, Maybe I should have gone to specsavers (Lotus with the Vauxhall engine!) :o
Not sure where you are coming from with the chain guard/tensioner but another avenue, mine is the N46. looks like I need a manual to investigate. I was concerned about the stepping motor which adjusts the valve timing; it that 'sticks.
After this manifold issue I was on the road to remove the MSport suspension and have a softer ride! my 65 year old bones would like to grow old (mature) in a more comfort zone. anyone want to swap?

Thanks for all your replies.
 
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