Troubleshooting runnability

[johnnydanger]

So my S seems to have gotten a little more finicky lately and doesn't seem to be running as well as it could. I recently hit 48,000 miles and did my maintenance: air filter, valve adjust, zeroed TPS, etc. For the past 10k... or maybe much longer come to think of it... my S has not idled consistently nor is the 2-4k rideability that great. It feels kind of like the bike is carburated and is "loading" up in that range and at idle. I've got a nice idle set at 1,100 rpm and once the bike is warmed up it'll sit there for about 10 seconds then rpm will drop and get a little lumpy at 800rpm (it kind of gargles like a carb running too rich) for 5 seconds then back to 1,100rpm for 5 seconds, etc. The same thing seems to happen cruising around town at a constant rpm below 3,500rpm, 5-10 seconds of good cruise then hesitation for 5 seconds or so, then fine again.

Also in the past year my fuel economy seems to have gone downhill a bit. Much of the winter I was getting around 27mpg around town just commuting! If I really restrained myself and did a whole tank below 4k rpm I could squeeze 34mpg out of it. But if I ride really aggressively on the backroads I get 37-42mpg no problem! It's like the FI closed loop runnability is way too rich.

So my first question is: Does anybodys S actually idle perfectly at 1,100rpm and just stay there without alteration? Or do all our bikes rpms 'cycle' like that?

And my second question is: I think this is related to an aging O2 sensor that is incorrectly 'switching' because of its age. Anybody else think this is a possibility before I plunk down my $130 for a new one?

I'm trying to get this fixed before my upcoming MotoGP trip... help!

[levert]

Check those little rubber nibs used to block the holes when you synch the tbs,they might be cracked allowing air in. This will cause the symptoms you have, don't ask how I know!
They are cheap and now I carry an extra set.

[JonyRR]

JD; something's up, bud. under 40 is not good; I get in the low-to-mid 40's despite running open loop (my CCP and 02 sensor is removed for my own reasons). Some things to check.
02 sensor. Ignition woes? (bad coil, plug cap bad; hunting at idle and random dropping of 1 cylinder is a good clue here)
air leak, as has been pointed out.
check the intake manifold boots; mine were both leaking when I pulled 'em...yamabond 4 fixes that.
deal with this BEFORE a trip to laguna.
If you want to drive down to tacoma, you can try the 02 sensor that came out of my S; it functions and is just sitting there on the bench....

[repoe3]

Originally posted by johnnydanger
So my first question is: Does anybodys S actually idle perfectly at 1,100rpm and just stay there without alteration? Or do all our bikes rpms 'cycle' like that?

And my second question is: I think this is related to an aging O2 sensor that is incorrectly 'switching' because of its age. Anybody else think this is a possibility before I plunk down my $130 for a new one?

I'm trying to get this fixed before my upcoming MotoGP trip... help!

well coming from experience with three S bikes, all running well, all of them did "cycle" at idle to some extent. observed the environment, temps, etc and saw that hotter temps affested it a bit and with the most recent S, during a track day, i had to run the fast idle lever up while i was gridding up, she would drop in revs without it and lug at the line. but once i rode her home, she mellowed out. ECU thing or something.

i would not count out the O2 sensor...and you should be able to get the same bosch sensor at any auto place for $80-$90, not sure what the cross-reference # is.

as for the throttle body nipples, worse case scenario, you could run a tube from one to the other and let them normalize that way...they were essentially running that way to begin with before the charcoal cannister and associated plumbing was removed.

and finally, you may want to consider some of the carbon removal tricks, just for good measure. there is the water torture test where you introduce water into the cyclinder (one at a time) via a small jar of water and a tube at the throttle body nipple. there are also some additives you can throw in there for a short ride that helps clean out the crud. there were some threads in the past here and on ADVrider about the procedures.

and extra finally, where are you hanging out while at the GP? are you going to have some super duper access that us mortals dont have hope to run into you while there.

repoe3

[850dunstall]

bmwst site had the following ongoing topic on the 02 sensor, the generic bosch untis is a lot cheaper, see the following thread

http://bmwsporttouring.com/ubbthreads/showflat.php?Cat=0&Board=UBB1&Number=520595&page=0&fpart=3

the poor mileage suggest o2 sensor, it will idle without the balancing plugs installed, but bad idle as suggested requires further investigation into ignition side

no joy...

c.l.

[bmwkid]

First if you have never done it do a carbon flush.
Then replace the O2 sensor I bet it will cure your bike,it cured mine at 40K.

[JonyRR]

JD; ping me offline if you want to use my perfectly-functioning 02 sensor.
Repoe/Bolter; I still have bolter's cellphone..we should hook up for a beer...I have an abridged version of 'take it to the limit' in mpeg format for that cool BMD dvd...

[repoe3]

Originally posted by JonyRR
JD; ping me offline if you want to use my perfectly-functioning 02 sensor.
Repoe/Bolter; I still have bolter's cellphone..we should hook up for a beer...I have an abridged version of 'take it to the limit' in mpeg format for that cool BMD dvd...

cool deal, i think there is a gathering saturday evening of some of the aprilia riders and such.

repoe3

[badger]

Originally posted by bmwkid
First if you have never done it do a carbon flush.
Then replace the O2 sensor I bet it will cure your bike,it cured mine at 40K.

Carbon flush....

Wazzat?

[johnnydanger]

Repoe: I'm staying up in Salinas at a friends place. We should definitely get in touch though. Go ride some of the coast down to Big Sur or something.

I should be getting down there friday night. For anyone that's interested in getting together, I'm not sure my schedule really, but give me a ring on my cell:

John Meloy
360 201-9039

[RBMann]

Mr. Danger I used a Bosch from Napa that cost $67 in N. Seattle. I just had to cut of the stock connector and then butt splice the wires together. The wire colors match. Moybin had posted the Bosch number MOYBIN O2 sensor

RB

[acidburn]

you didnt mention sparkers?

[johnnydanger]

I've replaced the plugs already. Just got my new plug wires and coil to install before I leave for the MotoGP. If it ain't any of those things I'll do the O2 sensor too. Thanks for the Bosch O2 sensor info.

Hope to see some of you in Monterey. Cheers.

[johnnydanger]

Hey RB, did you notice a tremendous improvement with the O2 sensor install?

[JonyRR]

how's the battery?????
amperage draw as well as voltage and individual cell health are all very important....

[RBMann]

Originally posted by johnnydanger
Hey RB, did you notice a tremendous improvement with the O2 sensor install?

A little less backfiring and surging. My bike has always surged and the backfires started with a Laser cat-elim.

RB