M47/N Diesel engine tips

A few tips when thinking of buying or indeed maintaining your M47/M47N engine, commonly found in early and later models of E46 2L diesels.

Most of the following points I make, and issues I describe with this engine is simply down to a lack of maintainence, not poor design or poor quality (with the exception of maybe the swirl flaps).

Points to note:

• Swirl flap (dependent on manufacture date). Can buy blanking plates in place of them
• EGR - clean it or replace it! Readily available DIYs on cleaning
• Turbo breather filter - make sure to fit the newer 'vortex' type. €18 for the filter itself
• Turbo - pop the intercooler hose and have a feel of the turbo shaft. Anything more than around 2mm of lateral play...or better still, if you can see in, any signs of fowling and its a re-con job or replacement in future miles. €500 recondition or €900 for a brand new OEM unit from the UK

Smoke types & reasons:

• Black smoke (continuous under load) = unburnt fuel, usually pointing to an air leak in the intake system. Usual places are the manifold pressure sensor gasket or the turbo pipe from the intercooler to the EGR (rubber flexi-joints crack and perish over time under boost)
• Blue smoke (anytime) = burning oil. Turbo wear/bearing seal leakage.

To help with a smokey engine, have a look at this DIY: http://www.bmwhaus.ie/forum/showthread.php?tid=45

Finally, flat spots in power delivery are usually due to an air intake leak or a MAF fault (€180-210ish for Bosch OEM replacement from Germany - DDE sometimes needs to be re-coded on fitment).