Closed Loop Operation

This page last updated Jan 15, 2009

Just about all ECUs fitted to cars operate as closed loop controllers whereas all controllers on bikes ( except some BMWs ) are open loop controllers. At least that was the case up to about 2003. Tighter regulations have since caught up with bikes.

Open loop and closed loop are technical terms used to describe feedback control systems. If you're not familiar with these terms, here's some simple examples.

Open Loop Example :
You are standing blindfolded in front of a shelf and you are trying to pick up an object on the shelf. With training you can be  learn where the object is. However if you change the environment in some way, i.e. wear high heel shoes (no I don't), your accuracy in finding the object is affected. This is analogous to tuning the bike on a dyno, then changing the exhaust pipes. The bike basically needs to be retuned for the new configuration.

Closed Loop Example :
Same scenario as above, this time you can remove the blind fold. You now have feedback as to where your hand is in relationship to the object. Now you can make the necessary adjustments so that you always connect. For the ECU, the oxygen sensor allows it to see what the mixture is and to adjust it to be the desired mixture. You can now change pipes, intake filters and the mixture will stay correct all the time.

Benefits of closed loop operation

The main benefit of closed loop operation is the mixture is always close to the optimal setting. Hence power and efficiency are always close to optimal. This does not mean that a map is no longer necessary though. Response times of the gas sensor and the controller mean that there will be a slight delay in getting the mixture right if the map is not right.

The type of lambda/gas sensor used greatly affects what is possible with closed loop operation. A cheap sensor will only allow closed loop to work at an air/fuel ratio closed to the stoichiometric ratio. This may be ok for the cruise areas of the map only. A more sophisticated sensor will allow any air/fuel ratio to be achieved.

MyECU Closed loop operation

Closed loop operation is enabled or disabled by SW1 on the MyECU. When the switch is on, MyECU operates as an open loop controller. An exhaust sensor is not required for this mode of operation. At any time closed loop operation can be enabled by fitting an oxygen sensor and turning the SW1 off.

It is possible to enable or disable closed loop operation for each individual cell of the map. Why would you want to do this you ask? Currently the closed loop software can allow one of seven target voltages from the sensor to be set. MyECU closed loop allows you to -

  1. run a richer mixture for wide open throttles (WOT).
  2. run a leaner mixture for the throttle back off.
  3. disable closed loop for total throttle off
  4. disable closed loop for idle
  5. disable closed loop for wide open throttles (WOT).
  6. run a leaner mixture for cruising.

With the optional Optimiser, the feedback from closed loop operation can by used to automatically adjust the map. Over time you will attain the perfect map for the bike's current configuration.

What Oxygen Sensors can be used with MyECU

I was quite surprised at the number of variants of oxygen sensors that are available. I would expect My16M to work with all the common types, although I have only tested with a few. The main variations in sensors are whether they are wide band or narrow band, and how many wires come out of it.

All the common types produce a voltage between 0 and 1 volt. Lean gives a 0 volt reading and rich gives a 1 volt reading. The cheaper sensors are narrow band and the voltage quickly changes as the mixture changes from rich to lean or visa versa. These sensors are digital in nature. There's no middle ground and all the ECU can do here is to keep the mixture correct.

Wide band sensors have a more gradual change in output. There are degrees of rich and lean. With these it is possible to be a bit smarter. You can have an acceleration/power mode where you run the bike a bit richer than normal, cruise mode where you run it a bit leaner, etc.

Sensors can come with 1,2,3 or 4 wires. The difference between 1 and 2 wires is that the two wire is isolated electrically from the exhaust. It has a signal and a ground wire that are wired straight into the ECU. The single wire relies on the ground being returned through the exhaust and engine and frame. This has more potential for noise and we don't want more of the earth problems that the bikes already have so I recommend the two wire over a single.

The 3 and 4 wire are basically the same as the 1 and 2 wire respectively. The extra two wires are for a heater element that is run off 12 V. For the same reason as above I recommend a 4 wire over a 3. The heater element is to speed up the warm up of the sensor as they don't work until they reach 400 degree Celsius. Without a heater it can take minutes to warm up, with the heater its about 10 seconds.

Originally I used the Bosch 0258 104 002. It's a 4 wire wide band sensor. On my bike the heater gets its power from the relay that powers the fuel pump, injectors and coils. This sensor is expensive.

Nowadays a new generation of 5 wire sensors is available. These require a dedicated box of electronics to drive the sensor. I recommend the LC1 from Innovate Motorsports in Califorinia. Not only does the LC1 perform better than the Bosch, it is cheaper also.

How to connect the sensor to MyECU

If you are running with the My15M and your bike has a sensor standard, you have nothing more to do. The sensor's signal is already routed to the ECU through the wiring harness.

The MyECU has a 3 pin header internally that is used to connect one or two sensors. You should have received the matching 3 pin plug with MyECU.

The middle pin is for the ground and the outer 2 pins are for the 2 sensor signals. If both the sensor and MyECU are properly earthed there is no need to use the middle pin.

The first sensor connects to the pin closest to the heatsink for the My15M, the pin farthest from the heatsink for the My16M and pin closest to the nearby capacitor for the MyP8.