850CSi Running Rough

[Job38]

Just got the old Beast out of the garage after 10 days Christmas hibernation.
Started fine but is running very rough and missing at low revs.

Any ideas out there?

[r5gttgaz]

Is it drivable? If so I'd go for a run then see how it behaves.

Could it be that the battery is taking a lot of juice?

[Job38]

Thanks for the reply.
Heeded your advice, took the beast out for a run.
Seems OK now.......
However, can't see how the batteries would cause that, started fine.
Felt like an old fashioned misfire.............
(Difficult to tell with a V12 though..........)

Anyone else know what it could be?

Oh, and Happy New Year, in anticipation.

[MitchT]

My 318is was very rough once after a week or so sitting unused during a cold, damp spell. It even cut-out after about five minutes the first time I went out and repeatedly cut-out when any load was applied when I tried to get going again... so I sat with it running for five minutes before attempting to set-off again and then it was happy to pull-away. There then followed an 'Italian tune-up' () and no further problems occurred.

Edited by MitchT on Monday 31st December 20:13

[parksie]

Job38 said:

Thanks for the reply.
Heeded your advice, took the beast out for a run.
Seems OK now.......
However, can't see how the batteries would cause that, started fine.
Felt like an old fashioned misfire.............
(Difficult to tell with a V12 though..........)

Anyone else know what it could be?

Oh, and Happy New Year, in anticipation.

Well her i am Baby sitting my new Grandson while all are outside getting drunkBut yes I have had similar happen to my 840, the Batteries proved to be on their last legs, & quite possibly even given that see fired up there is a possibility that ther was insuficient current to power the ecu's & electronic throttles.

Happy New Year All

[MitchT]

If it's the electrics that are at the root of the problem you'll need to ascertain which things are powered by the battery and which are powered by the alternator. You might want to get the alternator checked.

[Chester Drawers]

I'd bet money it's the batteries getting tired. I had the same problem, "Italian Tune Up" fixed the problem but it came back until I swapped the batteries.

Cheers

[Talkwrench]

8's are very sensitive to low batteries and many strange problems can manifest themselves. However, missing at low revs isn't usually a symptom!
I'd say that the most likely bet is weak ignition leads, suffering a little with damp.
If the leads are original, then they will be well past their best. A new set of Magnecors work absolute wonders with the V12's. Replace the Dist caps and rotor arm at the same time and you will find the engine gains a new lease of energy.
One of the problems with weak leads is that not only do you suffer from a poor spark but the cam position sensor fails to work correctly either (it is positioned round lead two on each bank).
This can also cause rough running and eventually throws up an engine error code.
Blue Magnecors can be persuaded to fit in the original lead guides and work out much cheaper (and better!) than original BMW replacements.