Code worry

QI need some tech advice. I have a 2008 BMW E90 318i Ci with the N43 engine. It’s got rough running at idle and these faults:

▶ 30EA Denox catalysator sulphur poisoning intermittent.

▶ 29CE Misfire cylinder 2 intermittent

▶ 29D9 Misfiring detection fuel tank level too low intermittent

I have tried swapping injectors, swapping coil packs and fitting new plugs. If I remove coil plug from coil number 2 the engine note does not change. The smooth-running values are really high on cylinders 1 and 2.

C & T Pells

AWith regard to the 29D9 code I am presuming that the fuel level in the tank is not low. The injectors on the N43 engine can be problematic and they do need coding to the cylinder and so swapping them round will not necessarily eliminate the problem as the injector will not then be correctly coded to the correct cylinder.

There is one other test which you have not mentioned carrying out and this is a cylinder compression test. The rough running and the associated codes may all be due to a mechanical issue with the engine such as a burnt valve or poor compression ring.

I would first ensure the compressions on all cylinders are within close proximity and then as your test has proved number two is the source of the problem, I would consider checking the connecting plugs to the coil pack and injector on number two cylinder. Look for any slight crack in the wire which may be preventing the circuit from completing, although having mentioned this if there was a break in the circuit, I would expect this to come up as code.

If none of the above proves to resolve the problem, then it may be worth taking out the injectors to get them professionally tested.