BMW R1100RT Throttle Body Setup on high milage bike

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Following my previous article on a Throttle Body Sync based from the Lentini Zero=Zero sync, I have a better understanding of my Motronic controlled injection system.

So, following hours of setup and testing and research, I have come to the following conclusions on a bike without a catalytic converter and no CO/lambda sensor. Following this learning curve and some great throttle angle and voltage measurements from the BMWMOA forum, here is my Throttle Position Sensor and Throttle Body sync procedure and some background information.

Background information

Acronyms

  • AMM: Analogue Multimeter (uses a dial with a needle)
  • DMM: Digital Multimeter (uses a digital readout)
  • TPS: Throttle Position Sensor
  • TB: Throttle Body
  • TDC: Top Dead Centre
  • MAF: Mass Air Flow Sensor
  • BABS: Big Arsed Brass Screw: Big Brass Screw on each TB that allows extra air to bypass the butterfly valves at low opening angles.
  • CCP: Catalytic Coding Plug: A plastic block that connects several connectors in the fusebox to get Motronic to use a specific fuel injection map
  • EMS: Engine Management System
  • CO: Carbon Monoxide

What Motronic EMS does at idle

  • If there are 3 bars or less on the temperature gauge, Motronic may automatically enrich the fuel mix, whatever the enrichment lever (“choke”) is set to.
  • When you go above 6 bars on the temperature gauge, the system is running hot, and will run fast and screw your settings up that you expect at normal running temperature.
  • The Throttle Position Sensor box actually contains 2 elements:
    • A potentiometer that tells the Motronic computer the position of the left hand side butterfly valve to calculate how much fuel to inject according to the corresponding butterfly position – the actual TPS itself.
    • A switch that tells the computer that the throttle position is at idle and forces the bike into a closed circuit mode and try to hold a pre-programmed idle tickover.
    • You can read the state of the TPS idle switch using the diagnostic plug under the rear saddle (connect pin 3 to earth, and then connect pin 1 to the negative connector of an analogue (needle) multimeter, and the positive needle connects to the battery. As you move the TPS between ~0.010v and ~0.430v, the switch will be active.
  • The TPS needs a minimum voltage: If it is set to 0.006v, the integrated idle switch will not be engaged and bike will run open circuit, and will run inject a basic fuel amount, and engine speed will vary only according to airflow.
  • Unless the fuel/air ratio settings are so far out of spec that it is not possible to physically hold the programmed idle engine speed, Motronic will do it’s damndest to hold a 1050 rpm idle tickover when the TPS voltage is between 0.010v and 0.400v, be it very lean or very rich.
  • Specific fuel maps may be applied depending on the Cat Coding Plug that sits in the fuse box. No CCP = Default maps.

Cat Coding Plugs and their influence on the Motronic computer

In the fuse box, you may finc a Cat Coding Plug (CCP). This looks like the other relays that sit in the box, except it is coloured. It contains nothing else but a bridge between different contacts on the socket base that uses the same pinout as a standard relay. You can make one yourself by connecting the corresponding numbered contacts on the CCP plug base with a wire and a spade clip.  These have been tested on 1100 RS & GS bikes  that use the same Motronic, the following plugs have been tested and found to have the following characteristics on a standard engine:

  1. No CCP – RS (Carbon Monoxide pot installed): Best power but high emissions and bad fuel economy
  2. Golden yellow CCP – RS (no CO pot): performance close to 1 but much better fuel economy
    – Connects contacts 30 and 87
    – CO pot seems to be ignored if installed
  3. Light blue CCP – RS (Swiss configuration): No power under high revs, wont go over 7000, may surge, bad performance
    – Connects contacts 30, 86, 87a
  4. Beige CCP – GS (With catalytic converter installed on GS): Good midrange power, but weak top end, no surging, CO default to 1.8%
    – Connects contacts 30, 87a
  5. Pink CCP – GS (Catalytic converter installed): Weak mid range power (worse than point 4 above)
    – Connects 30-87-87a
  6. Brown CCP – GS (No CO pot): Swiss settings, Starts but will not idle unless throttle held open
    – Connects 30, 86, 87, 87a
    – Tester had not driven bike in this config, but I suspect that it overrides the TPS idle switch and bike runs totally open loop and entirely depends on throttle tune rather than Motrinic imposing an fixed idle.

I would recommend either no CCP or connecting 30 and 87 (#2) for general running.

If you want to run totally open circuit, #6 seems to be the way to go, and then you set up your bike like any other carb bike with no intervention of the Motronic EMS on emissions or forced idle.

Your Motronic may be forcing an incorrect idle…

The forced idle happens when the TPS is under power – at least 0.010v – but less than a cutoff voltage of ~0.430v due to a switch in the TPS.

Whatever you set the TPS to in thisrange, and whatever you open the butterfly valves to, the bike will run – generally roughly – at about 1050 rpm. This is an annoyance, as the forced idle switch is making the Motronic use the TDC hall effect sensors to sense engine speed and change the injection rates to get the engine to hold this speed. As such, the TPS voltage itself between the 0.010v and 0.430v range is moot, and you can only really set the bike using the stop screws.

If you overcook the changes and go over the 0.430v and the idle switch opens, then the bike reverts to open circuit and will take off, so you only have a limited range of options, and ideally, you should change the stop screws, then twist the TPS back to the original voltage. The bike will also go open circuit if you fall below ~0.010v and may either die or speed up, depending on your air settings.

This means that you cannot work on the amount of injected fuel, but only on the amount of air being admitted.

This then throws 3 variables at you:

  1. When you adjust the butterfly position, your TPS will spin at the same time and increase, so your range of action is limited
  2. When outside of idle (idle switch disconnected), especially at highway speeds, the engine goes from closed to open loop, and your fuel to air ratio may be totally off even though at idle everything seemed happy due to Motronic correcting things behind your back. The fuel mix could be overly lean (bike runs ok but gets hot easily) or rich (bike runs ok, but drinks an excessive amount of fuel)
  3. Setting a low TPS value makes the bike difficult to ride as the bike will suddenly cut to 1050 rpm before the throttle is totally closed, and power will suddenly and brutally kick in even though you are gently and constantly opening the throttle, making for very jerky and uncertain low speed control.

Due to these points, your target TPS voltage needs to be between 0.327v – 0.386v, so that the idle switch is activated but you do not need to move the throttle much to go from an idle state to a power state and this avoids a bumpy and brutal low rev riding experience, and that the throttle plate is opening at the correct position (about 0.96° angle from closed and zeroed in the bore). From this, most of the air now comes via the BABS, that may need ~2 turns out from seated rather than the zero=zero’s 1.25-1.5.

The only thing you can adujust now is note your TPS voltage (ideally ~0.350) and then start setting up the left hand throttle body on the idle screws.

If your CCP is removed, then it is also very possible – this seems to be my case – that the Mass Air Flow (MAF) sensor in the air filter box inputs are ignored: This is a huge bonus, as this allows you to disconnect the air tubes from the throttle bodies and easily access the throttle stop screws for adjustment.

Tools needed for tuning

  • 14 mm Colortune spark plug.
  • 14mm plug spanner
  • Twinmax electronic manometer
  • 7mm socket
  • 8mm flat spanner (preferably one that has had the end cut off around the middle to half the length of the spanner as space is at a premium
  • 10mm flat spanner
  • Flat screwdriver
  • Long nose pliers
  • Analogue Multi Meter- used to read the TPS idle sensor
  • Digital Multi Meter used to display current TPS voltage

The TB From Scratch Setup and Sync Procedure

  • Set a digital multimeter to a DC millivolt scale (2000mV DC on mine)
  • Attach a small wire to Pin 1 of the TPS and connect to the positive (red) probe of a digital multimeter, set to read millivolts.
  • Attach the negative (black) probe to an earth point on the frame or the negative connector of the battery
  • Set an analogue multimeter to the first range abouve 12 volts DC (20v on mine)
  • Attach a wire to Pin 3 of the diagnostics socket and to an earth point of the frame or the negative connector of the battery (the plug numbers are written in tiny at the base of the diag plug)
  • Attach the negative (black) probe to Pin 1 of the diagnostic port under the saddle
  • Attach the positive (red) probe to the positive connector of the battery
  • Loosen the 3 hex head bolts on the TPS
  • Loosen accelerator cable lock nuts on left and right throttle bodies and wind cables in as far as they go (“generous” cable play)
  • Loosen the lock nuts on left and right throttle body throttle stop adjustment screws and back out screws as far as possible.
  • Throttle is now at absolute rest position – never leave the TB at this position when running as metal expansion can jam the throttle butterfly plates can move and jam in the bore!
  • Turn on ignition (but do not start bike!)
  • Checking both the DMM and AMM, twist the TPS as far as it will go to anticlockwise. DMM voltage should drop to 0.006v and AMM needle should be resting at zero. The idle swich (should) disconnect and voltage should not go lower than 0.006v
  • SLOWLY AND GENTLY twist the TPS anticlockwise until the AMM needle deflects to about 12v and note voltage on DMM. This is when the idle switch has connected and the TPS is really measuring voltage that the Motronic computer will use in closed circuit.
  • Note the minimum when the idle switch connects and deflects the AMM needle. Call this idle switch minimum, or iMin. It also confirms that the idle switch engages
  • Rotate slowly and gently the TPS until the needle on the AMM returns to zero (upper limit of idle switch disconnect).
  • Note the idle switch maximum voltage disconnect. Call this idle switch maximum, or iMax. It also confirms that the idle switch cuts out.
  • Checking that the accelerator is released, return TPS voltage so it registers 0.006v
  • Slowly and gently twist or tap TPS anticlockwise until a voltage starts to register by 1mv above base (~0.007v)
  • Screw in stop screw so TPS starts to register another millivolt (~0.008v).
  • Snap the butterfly valve to confirm that it is stopping on the stop screw and not jamming in the bore and it returns to this voltage.
  • Note the stopped butterfly minimum voltage on the stop screws. Call this sbMin. The wiper is engaged in the TPS pot and the butterfly valve is now being stopped by the stop screw and not jamming in the bore.
  • Increase TPS voltage to 0.250v by twisting it anticlockwise. Call this vInit. The idle switch should definitely stay engaged and should corresponds to the TPS base voltage specifications to register with Motronic.
  • Snap the butterfly valve to confirm that it is stopping on the stop screw and at vInit consistently.
  • At vInit, the AMM needle should still be registering a voltage, otherwise go back and check measurements. The butterfly needs to be closed (albeit lightly resting on a stop screw), the TPS needs to register 0.250v and the idle switch must be connected.
  • Lock the TPS hex head screws at this voltage. This is a fiddly operation and will take several tries.
  • Turn off bike, disconnect AMM and earth wire from diagnostic plug and reconnect to it’s rest plug under the rear seat. We should not have to use the diag plug or the AMM again for this procedure. Turn off AMM.
  • Using the left adjustment screw and the 7mm socket, close the stop screw until you are registering 0.340v on the DMM.
  • Unscrew both left and right BABS 2 turns.
  • Turn on Twinmax, set zero on minimum sensitivity, then go to max sensitivity, and readjust. Make sure that your Twinmax is on a flat and easily visible surface and set Twinmax to minimum sensitivity.
  • Remove vac port covers, and attach Twinmax hose A to the left side, and B to the right
  • Make sure Twinmax is on minimum sensitivity
  • Start engine. Make sure 4 or 5 oil temperature bars are showing.
    • If less, let the bike warm
    • If more, let bike cool
  • On Twinmax minimum sensitivity, balance right TB to match left.
  • Increase to max sensitivity, and make precise right TB balance to match left.
  • Set twinmax to minimum sensitivity, and shut down bike
  • Lock stop screws without moving them – this is an excessively fiddly job, It helps if you have a short 8mm spanner. Hold the lock nut with a 7 mm socket between your fingers, or with a flat screwdriver, and nip closed.
  • The bike should idle at 1050-1100 rpm. Fine tuning can be done with BABS and Colortune.
  • Start tightening left throttle cable to there is less than 1 mm free play on the cable before the TB rocker starts to move.
  • Set Twinmax to minimum sensitivity, check that it is still zeroed and restart bike
  • Lock throttle so bike is revving at 4500 rpm (equivalent to ~130 kph or ~80 mph)
  • Adjust right throttle cable to match and balance.
  • Increase Twinmax sensitivity to max and continue to fine tune right throttle cable.
  • Shut down bike
  • Refit vacuum port nubs
  • Hold cable adjusters with long-nose pliers and lock the 10mm lock screws on both sides.
  • Go for a ride. Idle and low speeds may be mildly rough, but high speeds should be fine, with smooth acceleration and no flat spots. 130 kph cruise should also be smooth.
  • Put bike on centre stand after a short test ride to confirm
  • If idle / Sub 2500rpm speeds seem rough:
    • Remove left spark plug, install colortune, and start bike. Check colour: It should be a bunsen blue, potentially a tad rich so some orangeness will be ok.
      • If orange/yellow: Mix too rich. Back out the BABS until bunsen blue
      • If dark/bunsen blue or tinged yellow, should be ok…
      • If pale blue or invisible: Mix too lean. Screw BABS in until bunsen blue
    • Repeat the same on right side
    • Check that spark plug cable is not deteriorating and/or shorting (check for clicking around the spark plug tube. Repair if necessary.

From there, all should be good.

2 thoughts on “BMW R1100RT Throttle Body Setup on high milage bike

  1. John

    Hi and thanks for the write up, I have a 96 RS that Im going to try and tune up as its running rough.
    My bike also has the Co pot like yours, would you be able to post the ohm values just so I know if mine are in the same ballpark figures?, Thanks,

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