BMW R1100 Engine Surging: Causes and Fixes

Understanding and Addressing Engine Surging on Your BMW R1100 Series

The BMW R1100 series, encompassing models like the R1100RS and R1100RT, are renowned for their robust engineering and touring capabilities. However, like any complex machine, they can occasionally exhibit issues that detract from the riding experience. One such common complaint among owners is engine surging, a frustrating phenomenon where the engine speed fluctuates unexpectedly, particularly at lower or steady throttle openings. This article delves into the intricacies of the Motronic fuel injection system, common causes of surging, and practical solutions for R1100 owners seeking a smoother, more predictable ride.

The Motronic System: A Brief Overview

At the heart of your R1100's engine management lies the Motronic system. Specifically, the Motronic 2.2 (and its close relative, 2.4 used in later models) relies on a sophisticated interplay of sensors to dictate fuel delivery and ignition timing. Key inputs include:

• Hall-effect triggers: These provide crucial data on engine speed and the precise moment the piston is at Top Dead Center (TDC), essential for ignition timing.
• Throttle Position Sensor (TPS): Mounted on the throttle body, this sensor communicates the exact angle of the throttle butterfly, indicating rider input.
• Intake Air Temperature (NTC): This sensor helps the Motronic calculate air density.
• Engine Temperature (Oil NTC): This informs the system about the engine's operating temperature.
• Oxygen Sensor: On models equipped with a three-way catalytic converter, this sensor monitors exhaust gases to fine-tune the air-fuel mixture for optimal emissions and efficiency.

The Motronic unit uses this data to calculate the amount of air entering the engine and subsequently determine the correct fuel injection pulse width and ignition timing. This complex calculation aims to provide optimal performance, fuel economy, and emissions control under various riding conditions.

The Enigma of "Cat Code Plugs" (CCPs)

A significant factor influencing the Motronic's behaviour, particularly concerning drivability and emissions, is the "Cat Code Plug" (CCP). These small connectors, when plugged into a specific socket on the Motronic unit, effectively select different pre-programmed 'maps' or calibration settings. These maps are designed to tailor the engine's performance and emissions to meet specific country or emission standards. BMW provided numerous CCPs for the R1100RS/GS series, each with distinct characteristics affecting emissions, performance, and drivability.

Understanding the Impact of Removing the CCP

Many owners have experimented with removing the CCP, often in pursuit of increased power. However, this action has significant implications:

• Open Loop Operation: Removing the CCP typically defaults the Motronic to an "R1100RS without cat map." This often places the system in "open loop" mode, bypassing the oxygen sensor's feedback.
• Increased Emissions and Fuel Consumption: Running in open loop generally leads to a richer fuel mixture, resulting in higher emissions and noticeably poorer fuel economy.
• Catalytic Converter Damage: The richer mixture can overheat and damage the catalytic converter, especially if it's still fitted.
• Default CO Setting: Without the CCP, the Motronic often defaults to a presumed 1.8% CO (Carbon Monoxide) mixture, especially if the optional CO adjustment pot is not installed. This can be confirmed by a dealer reading a "1111" fault code, indicating the CO pot is not detected.

It's crucial to understand that removing the CCP is generally not recommended if you retain the stock catalytic converter. Tests have shown CO readings jumping from a stock 0-2% to a problematic 6-8% without the CCP. This not only harms the environment but also significantly increases your fuel costs and risks damaging a costly emissions control component.

Experimenting with CCP Configurations

Rob Lentini's extensive testing on his R1100RS provides invaluable insights into the effects of various CCP configurations. While his findings were specific to the RS, they offer a strong indication of potential outcomes for other R1100 models like the RT:

Key Conclusions from CCP Testing

• Configuration #2 (Golden Yellow CCP) appears to offer the best compromise for R1100RS owners seeking a balance of performance, low emissions, and acceptable drivability, especially when retaining the stock catalytic converter.
• The CO adjustment pot seems to be ignored when used in conjunction with a "with cat" CCP.
• Removing the CCP without installing a CO pot triggers a "1111" fault code and forces the Motronic into a default 1.8% CO setting.
• For R1100RS models, configurations other than #1 and #2 are generally unacceptable.

The Critical Role of the Throttle Position Sensor (TPS)

Another crucial component influencing engine behaviour is the Throttle Position Sensor (TPS). This sensor, essentially a variable resistor, is directly linked to the throttle butterfly. It sends a signal to the Motronic reflecting the throttle opening, ranging from idle to fully open. The accuracy of the TPS signal is paramount for correct engine management.

Adjusting the TPS: Precision is Key

TPS adjustment is a delicate procedure best performed with the aid of a BMW MoDiTec analyzer, the same tool used by dealerships. The process involves clearing any existing fault codes and then carefully rotating the TPS until a specific reading is achieved on the analyzer. Once set, the securing screws are tightened, and the throttle movement is rechecked.

Recommendation: For most owners, it's advisable to leave TPS adjustment to qualified technicians. Incorrect adjustment can lead to poor engine performance, potential engine damage, and may even void your warranty. If you suspect a TPS issue, consult your dealer.

Troubleshooting Surging: Practical Steps

Before delving into modifications, it's essential to ensure your Motronic system is functioning correctly and free of faults.

1. Clear Motronic Faults

Any adjustments or changes made to the Motronic sensors can potentially trigger fault codes. To ensure accurate diagnosis and prevent lingering faults from affecting your results, it is imperative to clear the volatile fault memory every time you make a change. This is achieved by removing and then reinstalling fuse #5 (Motronic). For added safety, it's also recommended to remove and reinstall fuse #6.

2. Evaluate CCP Configuration

If your bike is experiencing surging, consider the CCP configuration. If you're running without a CCP and have a catalytic converter, refitting the appropriate CCP (like the Golden Yellow for an RS) might resolve the issue and improve emissions and fuel economy.

3. Throttle Body Synchronization (TBS)

Imprecise throttle body synchronization is a frequent culprit behind engine surging, particularly at lower RPMs. A super-accurate TBS can dramatically reduce or eliminate this problem.

Performing a Throttle Body Sync

For this task, a mercury manometer or a Twin Max tool is essential; basic vacuum gauges are insufficient. The process involves:

1. Ensuring some free play in the throttle cables (including the crossover cable on older models).
2. Setting both air bypass screws to 1.5 turns counter-clockwise from fully seated (2.25 turns for GS/R models).
3. Warming the engine thoroughly (at least 15 minutes) with a fan directed at the front.
4. Using the manometer or Twin Max to check the balance. Adjust the blue paint-sealed throttle stop screws on the inside of the throttle bodies to achieve balance and a steady idle of approximately 1100 RPM.
5. Once balanced at idle, adjust the synch crossover cable to balance the readings just off idle (around 1500 RPM).
6. For newer models (post-'97), set both throttle cables to 0.5mm free play and then adjust for correct synchronization.
7. Reset the throttle cable free play to 0.5 mm.

Important Note: After the initial setup using the stop screws, subsequent synchronizations should only be performed using the air bypass screws.

4. Valve Lash Adjustment

Increasing the valve lash can significantly improve low-end drivability and throttle response, and in some cases, resolve idling issues and surging, especially on cold mornings. Recommended cold settings are:

• Intake Valves: .006" to .012"
• Exhaust Valves: .012" to .014"

This adjustment can lead to a smoother idle, more immediate throttle response, and cooler valve temperatures with minimal increase in valve noise.

5. Ignition Timing Advance

While not directly a cause of surging, advancing the ignition timing can yield modest performance gains. Most manufacturers set timing conservatively. A gentle advance of around 3 degrees can add 2-4 HP across the RPM range. However, this must be done cautiously:

• Locate the timing plate securing screws on the crankshaft pulley.
• With the engine at 1000 RPM or less, observe the timing marks (S for initial advance, Z for full advance, OT for Top Dead Center) with a timing light.
• Loosen the screws and tap the timing plate counter-clockwise to advance the timing. Re-check with the timing light.
• Crucially, always use PREMIUM fuel when advancing ignition timing to prevent detonation and potential engine damage.

Advanced Modifications and Considerations

For those seeking further improvements or alternative solutions to surging, consider:

• Techlusion 83i Fuel Injection System: This aftermarket unit is specifically designed to address surging issues on R1100 models by providing more precise fuel control.
• Dow Corning Gear Gard "M": Adding a small percentage (3-5% by volume) of this lubricant to your transmission, final drive, and fork oil can improve shifting ease and reduce stiction in the forks.

Conclusion

Addressing engine surging on your BMW R1100RS or RT involves a systematic approach, starting with ensuring the core Motronic system is functioning optimally. Understanding the role of CCPs, the importance of a correctly set TPS, and the impact of throttle body synchronization are critical steps. By carefully performing these checks and adjustments, or by consulting a qualified technician, you can restore a smooth, responsive, and enjoyable riding experience to your beloved BMW.

Frequently Asked Questions (FAQs)

Q1: What is the most common cause of surging on an R1100?
While various factors can contribute, poorly synchronized throttle bodies and incorrect CCP configuration are among the most frequent causes of surging.

Q2: Can I remove the Cat Code Plug (CCP) to get more power?
You can, but it's not recommended if you have a catalytic converter. Removing the CCP leads to higher emissions, increased fuel consumption, and can damage your catalytic converter. It often results in a richer, less efficient mixture.

Q3: How often should I check my throttle body synchronization?
It's good practice to check and adjust your throttle body sync annually or if you notice any signs of surging or rough idling.

Q4: Is adjusting the Throttle Position Sensor (TPS) something I can do myself?
While possible, TPS adjustment requires precision tools and knowledge. It's generally best left to a BMW dealer or a mechanic experienced with the Motronic system to avoid potential engine damage.

Q5: What does clearing the Motronic fault memory involve?
It involves removing and then reinserting fuse #5 (and often fuse #6) to reset the Motronic control unit's temporary memory, which is crucial after making any sensor adjustments.

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