Knock on start up

[Mark Watson]

Hi Guys,

               I need your expertise with a niggly problem I have on a cold start up.

When I start her up there is a knocking sound from the engine area....I have been told by a BMW specialist that it is the NOX sensor. He advised me to regenerate by driving for 45 mins in forth gear at approx 65mph. I did this but it did not cure the problem. I have no warning lights and the car runs smoothly without any hesitations or coughs...Any ideas

Regards

 

mark.

.by the way car is 2010 e93 320i convertible with 74000 miles

 

 

 

 

 

 

 

[Greydog]

Hi Mark

Welcome to the Forum

Asking folks to diagnose a noise without hearing it is just about impossible. I also don't follow the Specialists advice, from what I have read the newer engines have 4 Lambda Sensors where earlier engines have 2, but their job is the same to measure the Nitrogen Oxide (Nox). They are mounted before the Catalyser and after the catalyser so that they can measure the difference and signal the DME to adjust fuel/valve timing accordingly. I think you have 2 catalysers so 4 sensors.A diagnostic scan should show any issues. 

The advice given seems to be inline with Diesel's to force a regeneration of the DPF (Diesel Particulate filter) 

If the knock is only on cold start? I would first check oil levels as low oil will let oil drain back to the sump which then would give several components the opportunity to rattle/knock on start up, once the engine has run and oil pressure is in the system no rattle/knock. If oil level is OK I would check for something loose in the exhaust that once warm expands and stops the rattle. 

Hope this helps

Dave

 

 

 

[Mark Watson]

Thanks for the info Dave...thought it odd about the regeneration, as my car is petrol not diesel, but he said it would reset the sensor...???
 

Ive topped up the oil so will try and see if there is any difference.

regards

 

Mark