RE: Poor Gas Mileage

["Minor, Bob" <MinorB@xxxxxxxx>]

I have a '96 R11RS with a Two brothers exhaust and CCP removed.  The O2 sensor is in place, I have done the 0=0 procedure, have Autolite plugs, GS tubes, use a Twin Max regularly and am anal about identically (between left and right) adjusted valves. I can honestly say it runs way better than when I bought it; it's quicker, smoother, and has no surge whatsoever.  

As for gas mileage, I rarely ride for a whole tank in town and really don't pay much attention to fuel mileage if I do.  I would guess that mileage in stop and go conditions is well under 40.  However when I am traveling (which is what I mostly use the bike for) and using a whole tank of gas at a time I regularly get mid to high 40's.  That's led me to believe that the potentiometer really only has an effect at idle or just above.    



- -----Original Message-----
From: owner-oilheads@xxxxxxxxx [mailto:owner-oilheads@xxxxxxxxx]On
Behalf Of Tom Brown
Sent: Thursday, January 22, 2004 2:07 PM
To: BMW Oilhead List
Subject: Poor Gas Mileage


Peter:

I have a friend with an earlier RS than yours.  His bike has no cat code
box.  He installed a Two Brothers no-cat exhaust and an early 83i Powerbox
(Fuel Nanny) to add a bit more fuel to compensate for the increased flow.
His bike ran great, but he was also getting mileage in the low 30s.   I
worked on his valves, FI settings and then the Fuel Nanny and, lo and
behold, mileage went up to 40.

I can promise you that your dealer is full of do-do when he says that
throttle synch is causing a 10mpg fuel consumption problem, especially when
you've pulled the cat code plug and are using a jumper.   The problem,
obviously, is the pulled cat code plug.  The fuel injection system is just
squirting more fuel than the engine requires.

Did you also pull the oxygen sensor?    Your bike will run very rich with no
CCP.  With a pot plugged in, mileage will be a bit better because just
having the potentiometer plugged in changes the fuel curve.   Settings of
the pot won't make a whole lot of difference, but the presence or absence of
the pot will.

No sense buying more CCP's. Just use a jumper and go to www.ibmwr.org and
check the oilhead tech section.  There is a long description of the cat code
plug situation and a chart that shows which terminals are jumped by which
CCP.  With this chart and a jumper wire, you can try ALL the colors, not
just beige.   It also explains the whole story behind the potentiometer.

If you have ANY CCP or jumper on the bike, you will get a different fuel
curve with "02 sensor plugged in"  or "no O2 sensor unplugged in".

If there is no CCP or jumper, the fuel curve changes for "pot" or "no pot".
The "no pot" setting is very rich and is probably what you are experiencing.
Pulling the CCP and/or jumper automatically disconnects the 02 sensor.  Even
it it's plugged in, it won't do anything with the CCP out.

Make sure you pull the #5 fuse for about 30 seconds each time you change a
jumper.  This will reset the computer.  If you don't do it, there will be no
change and you'll get all confused.

My friend's bike, in addition to getting better economy, also ran much
better, so there's another reason to find the economy problem.

It's not related to the throttle body synch.   If you have a throttle body
synch problem, you'll probably want to tackle that too, but you should solve
this one first.   If the synch is really bad, the bike will run very rough.

I like the idea of checking the voltage on the TPS (throttle position
sensor).  This is the black square box with an allen screw on each side on
the left throttle body.  You can recognize it because the right side doesn't
have one.  You need a digital volt meter to check this thing.  Instructions
for checking this voltage are on IBMWR.  The reading should be between 0.370
volts and 0.400 volts.  If it isn't, someone has adjusted something and you
should do, or have someone do (don't even ask the dealer), the "0=0"
procedure in Bob Lentini's article on IBMWR.  That will put your bike at a
good starting point.   Hint:  If you disclose your approximate location,
someone from this list who knows what their doing may volunteer to help you.

Adjusting the throttle position sensor box voids the warranty as does
installing an aftermarket exhaust in the first place.  This is pretty moot
since your bike is a '95.  Warranty is pretty much gone.   You've already
crossed over, so unless you can find someone to help you do these
procedures, I suggest you buy yourself some tools and read up.  PRINT OUT
ALL THE RELEVANT ARTICLES from IBMWR and give yourself a week to look
through them at your leisure.  Especially relevant is the 0=0 procedure by
Rob Lentini.  A couple trips to the bike to see what does what without
making any changes will also be helpful as you're reading through
everything.  When you've collected all the tools you need (it's all in the
articles) you'll be ready to go.    It doesn't sound like your dealer, no
matter how nice he is,  is going to be much help.   Most of them only have
factory training and this doesn't include special FI settings to compensate
for freer flowing exhausts.

I do not agree with Bob Hadden (although I usually do).  The throttle
butterfly does not let in a linear amount of air as you turn it.  The TPS is
supposed to be lined up in one position only.  Simply changing the voltage
by moving the box around may give you better economy, but it may also cause
the bike to run too lean at some RPMs which is very hazardous to your
pistons.  This is sort of a Russian Roulette way of fixing the problem.  The
cure may be much worse than the disease.

IF the TPS is set between .370 and .400  OR if you've got your 0=0 set by
someone who knows how to do this and you've adjusted valves and throttle
body synch and idle speed and you still have economy problems:

Suggestion: Get a Pot. (BMW Part Number and info at IBMWR) Try no CCP with a
Pot and see if that solves it.   This is the configuration for BMW markets
that don't require catalytic converters.  Properly set up bikes generally
run very well with aftermarket exhausts and no CCP.   Again, it won't matter
a whole lot how you set the Pot.  Just set it for the smoothest, smokeless
idle.  The setting will not affect running at other than idle speed, but the
PRESENCE of the Pot. without the CCP, will certainly affect the entire fuel
curve.

I know this has gotten long, but to really fix it would take a message
triple this length.

Best,

- -TB


> I have a '95 R1100R with a catless Remus exhaust and the catcode plug
> pulled. My mileage is only 17,000 and gas mileage is about 32-35 mpg.My
> mechanic tells me I should replace my throttle cables. He synced the
> throttle bodies, but the mileage is still low and tells me that the
> throttle bodies aren't staying in sync which is causing the low gas
> mileage. Collective wisdom would be appreciated. Will replacing the cables
> make a difference? Would a potentiometer? Would a tan catcode plug?
> TIA.
> Peter

------------------------------