Cat code jumper to cure surging

kwilliamson · Post by **kwilliamson** » Wed Jul 04, 2007 2:12 pm

I have an 02 S which is a good bike apart from the dreaded surging/crap fueling. I understand you can fit a jumper lead in the Cat Code box. I just need to know if this can damage the cat or not?

winger · Post by **winger** » Wed Jul 04, 2007 3:04 pm

Were did you hear about that?,and whats it supposed to do??

gus · Post by **gus** » Wed Jul 04, 2007 5:21 pm

hi
I think your referring to the removal of a catcode plug which has eased or elimated surging.Some bikes came with it fitted,some didnt.If i remember correctly it is the beige coloured plug in the front fuse holders.Left side rings a bell,but i aint 100% sure on that.What effect it would have the cat i dont know for sure.Getting rid of the cat with a Y piece has a benifical effect on the bike if not on the enviroment.But them again the manufacture of the cat aint exactly envirmently friendly.

Have you done a search on past threads?
gus

madman · Post by **madman** » Wed Jul 04, 2007 7:19 pm

LH fusebox at the front. Different bikes can have different plugs fitted. I would leave alone if the cat is still fitted.

johnl · Post by **johnl** » Wed Jul 04, 2007 8:58 pm

i think steptoe is the man to ask about that.

Try a search on ukgser

r550s · Post by **r550s** » Thu Jul 05, 2007 6:52 am

Only a proportion of people seem to report part-throttle surging, and it seems to be bikes of your era. It seems a solid guess to blame the closed-loop catalytic control - particularly since this control mainly operates in the part throttle region. The surging is probably caused by the closed loop control 'hunting' ie richening, then leaning the mixture in an effort to get it 'right'. Unfortunately, it does this despite the fact that you're on a steady throttle. Ideally, any closed loop system should be designed to avoid hunting altogether. This is why it's tempting to blame the motronic. However, you can make life easier for the feeble-minded motronic by giving it two cylinders running as evenly, mixture-wise, as possible - imagine the (single) lambda sensor trying to cope with emissions from a over-rich cylinder on one side, and a correct one on the other: it'd lean out the mixture, and the 'good' cylinder would go like the clappers on a too-lean mixture (does your petrol lawnmower race when its about to run out of gas?)
To combat surging, the starting point has got to be loving attention to the throttle balancing - setting the throttle cables etc. Fact. True love includes the 'zero=zero' setting of the throttle potentiometer.
Re. the 'cat code plug'. I don't know whether 'cat code' is the official name for it at all. It is present on the bike because Motronic Inc. decided to manufacture control units with facility for a range of fuel maps - the correct map for the particular model/spec/country of sale is selected via an external coded jumper located somewhere convenient in the wiring. The plugs are colour-coded according to their particular jumper configuration (I've seen white, grey, yellow, brown and invisible plugs) Removal of whatever plug (if there is one) fitted to a bike just gives the motronic a different code - and it uses whatever fuel map it equates to. As far as I know, this is all done for convenience of production - it allows flexibility of manufacture. There's no indication (other than foklore - hey, that can be right too!) that BMW conveniently gave us a plug to pull out if you junk the cat/don't like surging. But...that's not to say that it wouldn't help on some bikes - but that would be serendipity. These bikes are designed & manufactured to have a cat.
....they are also designed to run satisfactorily with correctly maintained throttle-balancing too!
Phew