Z3 high CO emissions M44 engine

[Davedougan]

davedougan said:
Today 12:05 PM
Z3 1997auto M44 high CO emissions
Hi my Z3 has failed the mot on high CO. Tester reckoned changing O2 sensor would fix it but I have my doubts. On checking live data with old sensor the voltage fluctuated between 0.020 up to around 0.800 on idle. On changing the sensor I still get the same reading so doubting the sensor. I don't want to take it for a retest and have it fail again so wondering if anyone knows any other common high CO causes. The short and long term fuel trims are sitting around 0% sht term and 1.6 long. Could the TPS have anything to do with it as on live data it sometimes shows not plausible then goes to idle.
Any help would be much appreciated 👍

[Vince70]

Try disconnecting the MAF and taking the car for an Italian tune up, I’ve two cars with the M44 and one of them always has trouble getting through the MOT on emissions and I’ve tried sensors, MAFs and a cat plus Breathers and a CV valve.

Last time I forgot to plug the MAF sensor back in and it went straight through but I noticed I do get a ticking noise sometimes on tickover when it’s warmed up and it’s not coming from the engine but a believe the exhaust manifold might have a hairline crack which only opens up when warm which would give high emissions and it’s common on the M44 manifold.

[Davedougan]

Thanks for that I'll give it a try. The part that puzzles me is when I hook up a scanner the voltage at the O2 sensor is fine when the car is cold and on open loop cycle but as soon as it switches to closed loop the voltage starts going all over the place, almost like it's a ECU issue. Puzzled!

Edited by Davedougan on Saturday 9th March 13:50

[naturalaspiration]

Air filter clean? If you have high CO then it's running rich and still your LTFT is slightly positive - It may well be that the O2 sensor is shot. Otherwise engine runs fine? What is the condition of the spark plugs?

https://goo.gl/images/7LDxqu

[Davedougan]

Hi, new O2 sensor fitted with no improvement. Changed the spark plugs but original ones were fine with no sooting evident or oiling. Looked like the "normal" ones in the pic you attached. Thinking maybe a shot injector but maybe clutching at straws but it's slightly lumpy at tickover.

[tracydeedance]

M44 engine's often are hard getting through emissions at the best of times when it's even fully serviced .
I would put some Forte injection cleaner in half tank and give it a good run driven fairly hard
Take it back to MOT stn well warmed up and ask them to do the emissions while the engine is still hot.
If that fails could be the cat.
Good luck.
Ps m44 z3 are all slightly lumpy on tickover

Edited by tracydeedance on Sunday 10th March 11:23

[henrycrun]

Maybe feel around the inlet pipework for split/cracked rubber

[Davedougan]

Thanks gents will try the injector cleaner. I checked the induction pipework even sprayed break cleaner all over it to see if it would get drawn in and change engine note...no joy. Will keep searching 🤔

[naturalaspiration]

Don't forget the air filter.

[Davedougan]

👍 done that too and put Wynns injection cleaner in and hammered it 40 miles on motorway so fingers crossed.

[Richard-D]

The comments about the fluctuating voltage made me chuckle. Don't waste time trying to work out what is wrong here, that is just how [narrow band] o2 sensors work. When in closed loop, the voltage produced by the sensor will bounce between 'too rich' and 'too lean' and the ECU will slightly adjust the fuel to keep that happening. When in open loop the o2 sensor will just indicate 'too rich' as the ECU isn't looking at it.

[Dave0321]

Sounds like a crappy cat. if fuel trims are fine (as they are) it should be running clean enough to pass.

You might need to ask them to get the cat nice and hot before they put the probe in the exhaust.

[iSore]

Could be one of those horrid 'Euro' cats - they're useless and can be a nightmare on MOT emissions.

[Davedougan]

Thanks to all the help, sorry for my ignorance on the fluctuation of the voltages...you live and learn. I put the fuel system cleaner through it and hammered it on the motorway and thankfully got emissions down enough to pass. It's the original BMW cat by the way
Thanks again.

[Vince70]

My original Cat broke up a few years ago and could hear it rattling about and was troublesome the year before getting it through the ticket.
I then bought a cheapo Eurocarparts one and that got it through okay but cheapo aftermarket cats never last long and your lucky to get a couple of years out of them and the following year I had the same problem.
Apparently you have to get the cheapo ones really hot to get them working okay for the emissions.