Subject: Re: Increased fuel consumption: issue resolved- but no logical explanation... Author: webhorn4477 : member since November, 2009 : 37 posts Posted on: 2010-03-01 17:41:56

henrikk wrote: >Less air more fuel. DME belives that your driving at high altitude (thinn air). Less air more fuel thats for cooling and for enhanced performance. DME did the right thing if not your sparkplugs could be melted down. <

Sorry, this is absolutely not correct- unless you know that the BMW DME is programmed to do so and why.

Reason: Every gasoline powered car with at least one controlled catalytic converter operates the engine with (or around, to be precise) the stochiometric mixture of 14.7 parts air and one part gasoline (in evaporated condition), to allow the catalytic converters to work properly and achieve good power and economy. That is also the reason why there are O2 sensors- to check the exhaust gas wether the correct mixture is achieved, and, if not, make the engine computer correct it. Luckily, this proportion of air/gas is also almost the best compromise for engine performance and fuel economy.

This is what every car computer of every make will always do all the time: try to reach the stochiomteric mixture in the combustion chambers via its sensors for lowest possible emissions. (Exception is only full throttle, where the mixture is SLIGHTLY enriched to improve torque, cool the combustion chambers and cat. converters.)

So, whenever there is a deviation from the optimum mixture, it is corrected in a way to achieve the abovementioned stochiometric mixture and get the best working condition for the cat. converters. The direction and amount of correction can on OBD-cars be read out as the adaption values.

This should mean again, when there is an air restriction, the DME/ECU has to lean out the mixture to prevent the engine from running too rich.

It does NOT mean that a mixture, that is too rich anyways due to air restriction, has to be enriched additionally to prevent overheating and create enhanced performance. Sorry, that is complete nonsense. It would actually DEcrease performance and destroy the cat´s because of letting unburnt fuel get into them.


So, if anybody knows more, feel free to chime in. Maybe it has to do with the way the MAF measures? Lower airspeed due to restriction causes wrong readings?

webhorn

• Increased fuel consumption: issue resolved- but no logical explanation... - webhorn4477 2010-02-28 19:02:13 (457 views)
  • Re: Increased fuel consumption: issue resolved- but no logical explanation... - henrikk 2010-03-01 09:59:46 (253 views)
    • Re: Increased fuel consumption: issue resolved- but no logical explanation... - webhorn4477 2010-03-01 17:41:56 (257 views)
      • Re: Increased fuel consumption: issue resolved- but no logical explanation... - henrikk 2010-03-07 15:44:17 (222 views)
        • Re: Increased fuel consumption: issue resolved- but no logical explanation... - webhorn4477 2010-03-17 18:51:08 (174 views)
          • Re: Increased fuel consumption: issue resolved- but no logical explanation... - henrikk 2010-03-22 08:04:59 (144 views)
            • Re: Increased fuel consumption: issue resolved- but no logical explanation... - webhorn4477 2010-03-22 15:40:54 (159 views)
  • Re: Increased fuel consumption: issue resolved- but no logical explanation... - Rajaie 2010-02-28 23:36:33 (250 views)
    • Found even better mileage! - webhorn4477 2010-03-19 07:11:37 (197 views)
      • Re: Found even better mileage! - webhorn4477 2010-03-19 22:20:26 (173 views)
      • Re: Found even better mileage! - poolman 2010-03-19 12:21:20 (166 views)
        • Re: Found even better mileage! - webhorn4477 2010-03-19 22:25:57 (179 views)