This BMW 3 Series E90 / E91 had the very common N43 engine.

It ran rough and had an obvious mis-fire when cold.

Stored trouble codes were as follows:

30EA DeNox Catalytic Converter, Sulphurous

29CD Combustion Misfires, cylinder 1

29D9 Misfire at low tank fill level

Our own technician notes: 

Car had very little use in recent times – due to COVID-19 restrictions etc.

The initial NOx loading figure was 1722mg which is certainly on the high side and not far off the 2000mg figure where DeNox Cat replacement would be recommended.

The smooth running value of cylinder 1 was 800. (Values between -200 and 200 are considered acceptable.)

Pre-cat O2 values were super lean. Readings of 0.4, 0.6 and 0.8mA were attained.

Various tests were carried out; General engine health was considered: Was compression good in all 4 cylinders? Was the ignition side of things up to specification? Likewise with the fuelling side….

After repairs, 2 extensive drive cycles were undertaken.

Sulphurous Values:

Before Repairs: 1722mg

After 30 min motorway drive: 1558mg

After a further 45 min motorway drive: 1353mg

Interestingly enough, Fault Code (DTC) 30EA DeNox catalytic converter, sulphurous never returned.

We were happy that the values were steadily ticking down after each drive cycle and therefore retuned the car to the customer. The advice was to continue with 20 – 30 min drives, avoiding short journey’s where the vehicle doesn’t reach operating temperatures.

The customer has been invited back in to us – in 10 days time – for a follow up appointment so we can assess how things are going. We don’t charge for these follow up appointments.