Only getting 30-35mpg - what should I check?

[College]

Recently bought an 03 Rockster and love it! Just Checked mpg and only getting 30-35mpg. I have been, to use that old fashioned phrase, 'making progress' but not going crazy bongos. Will check air filter and for binding brakes - any other suggestions?
Used to get 45mpg from my 955i Daytona which i suppose is more aerodynamic than the Rockster which must have a drag co-effiecient similar to an oak tree.

[jfslater98]

That does seem a bit low. Start with a valve check and throttle body sync. Plenty of helpful guides here and out on the Internet if you're not sure what that is. After that, you will probably need to see if a stick coil has gone bad. Even though you have a Rockster, there is more collective knowledge posted on the R1150R thread group, as our bikes are nearly identical, mechanically.

For reference, I get in the low 40s, but do mostly highway commuting. Good luck.

[iowabeakster]

I think the Rockster has a shorter 6th gear than most of the Roadsters. My Roadster has the taller 6th gear and I get around 43mpg most of the time. Sometimes I get about 50mpg. The only time I got less than usual, was when I was sure I got a tank of bad gas.

While I was talking with Towerworker a while back, I remember him saying that one of his coils had gone bad. The bike ran pretty well, his only indication was that his milage had dropped noticibly. So I second jfslater's recommendation to check the coils (and yeah, spark plugs also).

[jfslater98]

And my last tank seems to be around the 35mpg range.

So it looks like we'll have some notes to compare over the next few weeks.

EDIT: forgot to mention that I had to take my exhaust tip off for this last tank. Hard to believe the little bit of back pressure would have caused it to suddenly run so poorly. It must be something else. Maybe extra vibrations caused one of the screws on the tip to back off.

[boxermania]

My bike with mods and driven with enthusiasm always returned between 42 and 46 mpg on 89 gas, irregardless of where in the US I happened to be visiting.

Suggest in order:

Air filter
Good TB sync
Stick coils on 4 plug models
Worn plugs....re-new and gap .030" to .032"

[College]

Thanks for the advice but in the end took it too the BMW dealer in Northampton. Very helpful but was told the "fuelling system has been modified - looks like a professional job - but our computer wont talk to it now - only thing we can do is put it back to how it should be and go from there -lots and ots ££££!"

So bit stuffed at the moment - will start another thread and see if anyone can advise about what might have been done. I feel a long journey starting.

[Rog(UK) - Yorkshire Dales]

30 - 35 miles per UK gallon is horrendously bad. My Rockster is completely standard but I get 50mpg easily and often knocking on 60mpg (riding carefully, but with the odd wild moment!)

Rog

[boxermania]

College

Can you be a bit more specific as to how the fuel system has been modified? Cat eliminator and can? Techclusion R259? Power Commander? Bypass the airbox and go with independent filters on the TB's?

[College]

Thanks Boxermania. Will give as much detail as I can but as you will see not really technically expert.
*The Cat has been removed and a Y piece fitted.
*Original exhaust now on the bike but I dont know if this was put back on after the work was done to sell the bike on with the replacement exhaust being kept.
*Now I do get out of my depth - it looks to me as if additional wiring has been installed on the left hand cylinder injector area when compared to other bikes. I will take a picture of it tonight and post it up.

Have not had it apart to see what if anything has gone on in the airbox but I can manage this so will have a look this weekend.

How could I find out by looking if it has a Techclusion R259 or Power Commander fitted?

Thanks for your patience.

[riceburner]

Thanks Boxermania. Will give as much detail as I can but as you will see not really technically expert.
*The Cat has been removed and a Y piece fitted.
*Original exhaust now on the bike but I dont know if this was put back on after the work was done to sell the bike on with the replacement exhaust being kept.
*Now I do get out of my depth - it looks to me as if additional wiring has been installed on the left hand cylinder injector area when compared to other bikes. I will take a picture of it tonight and post it up.

Have not had it apart to see what if anything has gone on in the airbox but I can manage this so will have a look this weekend.

How could I find out by looking if it has a Techclusion R259 or Power Commander fitted?

Thanks for your patience.

I would NOT recommend running the bike too long with the OE can fitted to a Y-piece.

Don't worry - it won't do any damage - but the can WILL run a lot hotter than usual.
Hot enough to melt a hole in your pannier - which happened to mine.

By all means keep running the bike that way - but don't fit a pannier to that side if you can avoid it.

[boxermania]

Look under your seat normaly the "fuel nanny's" are attached to the back ofthe airbox with velcro. Yes, additional wiring will be evident, like a piggy back connector attached to either the left or the right side injector (only one) as the injectors both fire at the same time.

Still, even with the current Y pipe and the stock can, the mpg should not be that low, unless you are riding at extremely high speeds.............

[College]

Thanks Boxermania- have had the seats off and no "fuel nannys" there but evidence of wiring changes.

Have put some photos up at: http://photobucket.com/college-07

They show: Some one has at some time spliced into the airbox sensor, unconnected red wire near fuse box, evidence of a cut earth in the same area and pictures of the left hand throttle body showing what I think is aditional wiring / connectors? - photos will make more sense I hope.

What I suspect has happend is that someone has had a Power Commander or something similar and pipe and then half removed it before selling on the bike? Have written to the 2 previous owners I have details of - there are 4 altogeather - to see if they can shed any light on the matter.

Not riding that fast to warrant 30-35 mpg! I wish.

Riceburner - do not have panniers so not a problem of them melting - can does not seem to get much hotter than normal though

Thanks guys for all the help -much appreciated.

[boxermania]

Looked at your pics and the bike has been heavily modified.....

The piggy back on the injector is indicative of a "fuel nanny" of sorts (Techlusion or PowerCommander), based on the mods it could even be home made.....try to follow the bundle back and see where it leads you to.
The airbox sensor measures ambient temperature and a typical mod to enrichen the A/F mixture is to place a resistor in parallel to fool the computer into seeing a colder temp, ergo a richer mixture.
The TPS (throttle Position Sensor) piggy back wll also affect the voltage that the computer sees as a function of engine load, as above, it will also affect the A/F ratio curve.

One of the owners new their electricity, the functionality of the sensors and how they interact with the computer algorithm. I also saw that the battery was BMW brand, would one of the owners be a BMW Tech? The real question is: What was the state of all the mods at the time you bought the bike?

This merits further dialogue, if you want, call me at (225) 445-6922 after 6PM CT and we can puruse the problem further.

[College]

Thanks Boxermania - you too know your sparks!
I only bought the bike a month ago and since I have had it done nothing to it. I test rode it at the time and it ran fine and indeed has run well since. It was only when I had used two tanks of petrol that I realised all was perhaps not as it should be. I have never owned a BMW before so did realise at the time of purchase that it has been modified.
I bought it from a small non franchised dealer about 80 miles away and he is not returning my calls to discus!. In any event I like the bike bought it at a good price and would like to get it sorted out.
I have written to two of the previous owners to ask them if they had anything done to it -one has replied saying know and the most recent owner has not yet responded I will let you know when he does. – There are two other owners who I cannot track down.
Tracking back the wires will test my competence and understanding what I see will probably be testing it too destruction – but I will strip it back a bit more and let you know.
I think where I will end up is taking it to http://www.tts-performance.co.uk/homepage.shtml who are only about 30 miles away and were helpful on the phone. They fit Power Commanders and Techlusion so will hopefully be able to advise.
PS Are you planning a trip to the UK in the next few weeks – we 80 miles NW of London Just outside Warwick and you could see it all for yourself!
Seriously thanks for sticking with this one and I will give you a call to discuss once I have sorted out the time zones.

[boxermania]

Never figured that you were across the pond, nevertheless these bikes are sturdy and simple to maintain and I encourage you to get your hands dirty. In this instance, you can trace the wire bundles back and see where they go....however it might be best to have someone else look at it and learn from it.

Once again, let me caution you that the person that modded the bike knew their P's and Q's, make sure that the prerson(s) that wil be looking at the bike have the electrical knowledge, both brand and mods related, if not, move on.

I have always wanted to visit the UK....unfortunately it has never come to pass.

You can count on my support, keep me informed.

[boxermania]

Looked at the TTS site, quite impressive with regards to supercharging and ECU mods....I believe they will be able to guive you some guidance....they have a supercharger app for the GS.

[deathtriforce]

i was wondering if a leak in the exhaust would also cause gas mileage to drop. I'm pretty sure I'm only getting about 20-25 mpg at most. Thanks guys

[College]

Booked the bike into TTS Performance Engineering tomorrow - I will let you know what they come up with.

[College]

Boxermania, bit of an update: TTS have had it apart and have discovered that it does indeed have a Power Commander fitted - it was right underneath the tank. Tou were right all along. They have had it up on the Dyno and downloaded various Maps from Power Commander but they are not sure what is up as according to their sensors it is not running rich - they are not sure if the maps are down loading and not sure at the moment that it has been wired in correctly. The Techincian who does all their Power Commander work has been away this week but is back on Monday and he will have a look at it then.

So we are getting there - further installments to follow!

[boxermania]

Well ????? Have you found anything yet?