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DIY Accelerator or Booster Plug devices (R1150RT)


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I've done a big ride yesterday afternoon with a temperature of 8 C


Even if I have a faulty stick coil, I was surprised to see that there was just a slight hesitation between 4000 to 5000 RPM


I'm still amazed by the spark plug readings after the ride was done. It is lean as I never saw on any engine. I read last week about resistor in series with the IAT to give false temperature readings to the ECU for richer mixture.


Some talk to add 1K to1.5K resistor. Do someone tried this trick ? if yes what resistor values they tried ?





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Morning legarem


On the BMW’s I have fooled with IAT resistors on everything from the 1100, 1150 to the 1200 hex.


In my opinion not a lot of gain to be had on the BMW boxers as the fueling computer doesn’t use a lot of intake temperature input for fuel trim on a warm engine (mainly used for starting trim)


In fact once in closed loop the intake temperature has no effect on fueling trim as the one and only fueling input used in closed loop is the 02 sensor. It does drop off the 02 sensor (goes open loop) on major throttle movement, at high RPM’s, or under very heavy load, etc.


If you disconnect the 02 sensor the fueling computer then goes back to using fixed mapping relying on the input sensors like engine RPM, engine temp, TPS, intake temp, to trim the basic fueling at steady throttle cruising.


You can try adding resistance in series with your stock IAT but the IAT used for intake fuel trim isn’t a simple linear resistance vs temperature thing. The IAT resistance system is complex so just adding a fixed resistance might work at 60°f but be way too little at 80°f. As an example—at appx. 40°f your IAT is around 4.7k but at 90°f it is closer to 1.65K.


I have some pretty sophisticated non linear IAT spoofers I have made up over the years to deal with the odd input curve of the IAT. Mostly used on other brands of bikes (the older open loop Ducati responds extremely well to an IAT spoofer.


If you want to try to spoof your IAT to see if it makes your bike a bit better don’t try anything exotic to begin with. Just unplug your IAT sensor and stick a 5.5 K resistor in the removed plug to see if that helps. Then maybe try a 7.5k resistor. If you see an improvement then you can go about building a proper temperature compensating spoofer that will maintain an input relative to ambient intake temp.



BTW- very white appearing sparkplugs are normal on the newer closed loop BMW’s due to the 02 sensor holding the fueling to close to 14.7:1 and the use of unleaded gasoline. You want to see some color in those plugs put a tank full of leaded 100LL fuel in from your local airport but that will probably ruin your catalytic converter.


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I looked at the Bosch temperature sensor and made some measurements. It seems mostly as this Bosch graphic which is not the 1150 sensor. Even if it is curved a little bit, between 0 and 30 C it can be considered near a straight line.



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Peter Parts

Having trouble distinguishing "straight line" from "exponential"? Don't matter, we know what you mean. And besides, only a very small piece of that line counts, at least for biking on planet Earth, hardy Canadians excepted.



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Doesn’t matter straight or curved just look at the gain per degree. On the 1100/1150 BMW IAT sensor the ohms per degree at 40°f is close to 117 ohms, with the ohms per degree at 102°f is closer to 13ohms (actually measured).


Then compare that to Motronic Ma2.4 air temp fuel trim tuning chart and you will see very little fuel trim change in the mid range. To get a meaningful change in air temp fuel trim it needs to have a lot of resistance added at highest temps and very little added at lower ambients.



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