320i oil leak on wiring

[johnwindwood]

Guys

My Son had a problem with a misfire on his 320 a few weeks ago. He called the AA, who diagnosed the problem as being oil contamination on the injector wiring-there is a large plug and socket mounted on the engine block on the passenger side under the inlet manifold. Cleaning it solved the problem, but there is a lot of oil around there still and it's not clear where it's coming from.
I have changed the cam gasket and rubber plugs as a precaution but does anyone have any ideas where oil could be coming from to land on that plug? Anything on the inlet manifold for instance?
Cheers

[blazed]

Having just read your other question i woulds guess the breather hose is loose under the manifold letting the oil drip down, it should plug into the side of the throttle body. link coming up. https://www.google.co.uk/search?q=m20+p ... oLaKJkPdDM:

[Brianmoooore]

There is a spring loaded tube that runs from the underside of the inlet manifold to the engine block that is sealed by an O ring at each end. This tube carries most of the oil draining from the top of the cylinder head to the sump, and if the O rings are old and brittle, or haven't been seated properly after refitting the inlet manifold, will certainly leak oil onto that side of the engine.
I can't really see why oil, an electrical insulator, should have any effect on the signals passing through that plug and socket, however.
There are known problems with this plug and socket though, and a TIS issued by BMW to prevent the problem.
If water gets into the plug and socket from above, it is trapped inside, and causes an electrolytic corrosion of the wires where they connect to the pins of the lower half. The wire that is the most affected is the one that carries the coolant temperature signal to the engine ECU, making the ECU think the engine is cold when it is hot, which will make the engine misfire at idle because of an over rich mixture.
I think the most likely scenario is that the connection for this sensor was failing, and the AA man's action of taking it apart and reassembling it has made a (temporary?) cure.
The TIS was simply to make a small v shapet cut in the rubber boot of the lower connector, so that any water in there can drain out.

[johnwindwood]

Thanks guys-will explore further. How difficult is removing the manifold?

[Cloggy Saint]

Not difficult but time consuming. Best done after removing the airbox, throttle body and anything else that restricts access to the hard to reach nuts on the inlet studs. The nuts nearest the bulkhead are a complete sod to get at and even harder to put back. Don't forget to de-pressurise the fuel system before removing the pipes from the fuel rail.

[Brianmoooore]

Don't forget to de-pressurise the fuel system before removing the pipes from the fuel rail.

Start the engine, and pull out fuse 11 in the fusebox. This will stop the fuel pump, and the engine will stop a few seconds later, with the system almost fully depressurised.