Re: bmw-digest V9 #2239

["Nick Pashley" <nickpashley@xxxxxxxxxxxxxxxx>]

> Date: Tue, 17 Sep 2002 14:33:57 -0700 (PDT)
> From: Michael <mike5635@domain.elided>
> Subject: Tech question...engine miss
>
>
> Questions:
>  1.  What is that slightly oily plug telling me?
>  2.  Did I miss something obvious?
>  3.  Am I an idiot...er.....
>
The oily plug tells you that it is not getting hot, which means that the
plug is either a) not sparking, b) not sparking at the right time, c) the
fuelling is wrong in that cylinder, d) compression pressure is low.

I don't know much about your engine, but I would assume it is sequential
multi-point fuel injection, and from you ignition description, has a single
coil and distributor, therefore the possible causes are:
a)     i)    Faulty plug - but you have changed this.
        ii)    Faulty ignition lead - my tip for the top
        iii)    Faulty coil - but unlikely to fail on only one cylinder
consistently.
        iv)    Faulty dizzy - but you have changed this
        v)    Faulty signal from EEC - again unlikely to fail on one
cylinder consistently.  Possible triggering problem (is this on the
flywheel?)

b)    i)    Faulty signal from the EEC - but why on only one cylinder?
Again, a possible triggering problem.
        ii)    Faulty dizzy - as above

c)    i)    Faulty injector - no. 2 fave
        ii)    Faulty signal from the EEC - comments as above

d)    i) test with a compression gauge - probably likely to see loads of
blue smoke due to oil burning if this was the case (never had such a failure
but unlikely to switch on and off like you have seen).  You could smell the
oil to check for signs of gasoline contamination.

If it were my engine, I would, in order of:
1.    replace the spark plug lead connecting to the oily plug
2.    swap injector with another cylinder and check the results
3.    check the compression
4.    check the EEC triggering circuit
5.    scratch my head

I don't think you have missed something obvious, apart from lending your car
to your brother-in-law!  And no, you are unlikely to be an idiot!

Let us all know how you get on.

Nick Pashley

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