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Thread: 99 R1100 RT - Surge is gone - Cheap Fix?!

  1. #16
    Registered User roger 04 rt's Avatar
    Join Date
    Oct 2011
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    Massachusetts
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    1,284
    ... Basically the Motronic on the 1100 doesn't provide quite enough energy to the coil, and also does not adjust ignition timing to deal with various gas octanes or pinging conditions. Also the O2 sensor is the on/off variety so at idle the ECU is dithering between too lean and too rich all the time. ...
    There are provisions in the 1100 and 1150 for low octane fuel. It requires a change of coding plug. Here are the plugs for the 1150GS

    30-87 standard

    30-86-87 low octane

    In closed loop, the normal swing is from lambda 0.97 to lambda 1.03. In my book that's a swing from a little lean to a lot lean.

  2. #17
    Registered User
    Join Date
    Jun 2012
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    213
    Ah ha. So the sensor itself is analog?
    My MINI (also a BMW) is supercharged, and I can put any old gas in it without pinging. It does this by first of all detecting ping (or maybe measuring the resistance at the plug gap?), retarding the ignition and enrichening the mix until the ping goes away. If you give it 91 octane it will make slightly more power and will get better fuel mileage (slightly). It effectively does the code-plug changing on the fly.
    I don't have an issue really with a 2006 MINI having more sophisticated electronics than a 1998 RT but that is where the fault lies.
    At 600 feet above sea level my RT will ping on 89 octane. But we're talking 80 to 100% throttle opening too. So I just back the throttle off a bit.
    I try to use 91 octane and with the cleaning and adjusting I have a smooth running motor.
    I guess I could mix the two available numbers 50/50...

    I do try to stay away from 93 octane when I head over to the Smokies since it doesn't do anything useful and may actually not all get burned before being dumped into the catalytic converter. Pay more money just to overheat the converter?

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