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Old 08-27-2012, 05:13 AM   #90
roger 04 rt OP
Beastly Adventurer
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Joined: Nov 2011
Location: Massachusetts
Oddometer: 2,296
On Saturday I got around to boosting the fuel pressure to match my Wideband O2 setting of 13.8:1. I used an Aeromotive 13301 (picture below) and increased the fuel pressure from 43.5 psi (3 bar) stock to about 52 psi--install photos later. Although a BoosterPlug configured for -30C or just letting the Motronic "adapt" work, I wanted to input the actual air temperature and adaptation is a slow process.

Bottom line: My R1150RT is running its strongest and smoothest yet. The pull from about 2,000 RPM on up in 4th gear is strong. Fifth and Sixth gears are similar but a bit higher on the RPM. The bike is now stock except for the Wideband O2 and higher fuel pressure, and the Motronic has a direct connection to all sensors.

Here's why I have decided to boost the fuel pressure. BMW has done a good job designing the basic fuel map for the 1150 and I don't want to lose their design knowledge--they have a good map of RPM vs TPS (how much air is going into the engine), they just plugged in lean fuel values. Look at the fuel map for a Ducati that I linked from Brad the Bike boy's site. This is not the same map as an R1150RT but it can illustrate some points.

You can see that it has 16 RPM columns across the bottom and 16 throttle angles up the side. This table holds 256 values that specify how long, in thousandths of a second, to turn on the injectors for certain RPM and throttle positions--based on their detailed knowledge of how much air the engine draws at each point. These values are only valid for gasoline without ethanol, and for one air temperature, one barometric pressure and for 43.5 psi fuel pressure. The R1150 has sensors for actual air temperature, barometric pressure and battery voltage. Then it uses the O2 sensor in Closed Loop to determine the actual fuel pulse needed to correct for ageing and component tolerance and E10 fuel. It compares the actual pulse calculated by Closed Loop to the fuel table and comes up with a correction factor. BMW calls these correction factors: Adaptation values. From all the reading I've done there is probably no more than a 4 X 4 table of Adaptation values, maybe fewer. And these values change slowly. And while you're waiting for the slow change your bike doesn't run it's best.

The numbers in the table have been designed for a Closed Loop mixture of 14.7:1. When I fill up with E10 fuel, it would be better if every number in the table were 4% larger since ethanol is a leaner fuel than gasoline. Since I've moved the Closed Loop to 13.8, that means the numbers should all be 6% higher. So 6% for my AFR change and 4% for ethanol means I would like every number in the table to be 10% larger.

It's not really possible for us to go in and change the numbers in the table to make them 10% bigger. But you can boost fuel pressure by about 20%, and the injectors then squirt 10% more fuel using the stock map numbers. This means the fuel table now matches my wideband O2 setting of 13.8:1. And that means the Motronic doesn't have to work hard to Adapt the two to match.

The fuel pressure regulator has done away with the need for a BoosterPlug to richen the Fuel Map (The BP works by lowering the temperature the Motronic sees) and now I'm running without one.

As an example of Adaptation, I'll add some tables in the next post.

I've only had one day of running but the combination of wideband O2 and add-on fuel pressure regulator looks like a winner.

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