Subject: Increased fuel consumption: issue resolved- but no logical explanation... Author: webhorn4477 : member since November, 2009 : 45 posts Posted on: 2010-02-28 19:02:13

As posted here: http://www.bimmerboard.com/forums/posts/751267
i had an issue with increased fuel consumption of about 10% after replacing the vanos seals on my ´01 E39 530i touring, manual. The good news first: the issue is resolved now. The bad news: I actually can´t find a logical explanation WHY it is resolved. Story goes as following:

I did, as mentioned as planned in the abovementioned thread, at first check the fuel pressure because i was thinking of an ageing fuel pump. This showed no abnormalities.
Then i again checked and double checked for all sorts of vacuum leaks- without findings. While i had the air cleaner housing disassembled and had no other idea of what to check, i took a strong wire, bent it and poked it in the main air intake tube which, on the E39, runs from the air filter housing to somewhere behind the front bumper. And there i got my first find: somehow, due to an unfortunate circumstance, a small stick had somehow managed it to get jammed in this passageway. Leaves had collected in front of it, and judging by the amount of "biomass" that came out of the (very large diameter) tube, all of this had been blocking this passage for the intake air completely. I have to say, due to the construction and position of the intake on the E39, this is a very unlikely condition to ever happen- but it did with me. The engine was getting its air only through the smaller tube, that runs from the air filter housing into the left fender on an E39.
Having fixed that, my multiplicative active mixture values dropped from about 8% to about 4.5%. This was a step in the right direction- but it´s not logical. The engine didn´t get enough air- so why did the DME enrich the mixture, not lean it out?!? Some sort of failsaife mode, in case of erratic sensor readings (air mass sufficient for low- to midrange driving, but not for high loads causing implausible values?)
Anyways, mpg´s improved a little- but not enough. :-)

The next thing i did (don´t try this at home, kids- professional driver on closed circuit): added half a quart of ATF to the engine oil- originally to clean out the lifters. Since my engine is very old and has high mileage, i´m quite willing to experiment. I know my engine and it´s behaviour, do precisely monitor it and can react in seconds if anything appears to go wrong.
This improved mpg´s too- a little. Though i don´t yet know why. It cleared the two seconds of lifter tick on very cold starts, but it especially smoothed out the transition between engine braking and stepping on the gas ever so slightly again. Before, there had ALWAYS been a little "bump" and no stepless transition possible (also to be seen on the economy meter), now absolutely smooth. It also let my mixture values drop to about +2.5%. Has anybody got an explanation for this? Freed up rings/increased compression?

The third an final thing i did: I replaced the engine mounts. Thats where it finally becomes completely illogical. I replaced them because i had some vibration and clutch problems, the car has quite high mileage and is a manual, which is hard on the mounts. Right after i took off for a test drive, i noticed, exept for the smoothed out engine running characteristics and cured clutch problems, an extremely decreased fuel consumption- exept from the cold weather, it was finally even better than before the seals change!
Now, whoever has a logical explanation for THIS, gets a lifetime supply of free vanos seals changes from me! :-)

webhorn

• Increased fuel consumption: issue resolved- but no logical explanation... - webhorn4477 2010-02-28 19:02:13 (799 views)
  • Re: Increased fuel consumption: issue resolved- but no logical explanation... - henrikk 2010-03-01 09:59:46 (535 views)
    • Re: Increased fuel consumption: issue resolved- but no logical explanation... - webhorn4477 2010-03-01 17:41:56 (500 views)
      • Re: Increased fuel consumption: issue resolved- but no logical explanation... - henrikk 2010-03-07 15:44:17 (445 views)
        • Re: Increased fuel consumption: issue resolved- but no logical explanation... - webhorn4477 2010-03-17 18:51:08 (378 views)
          • Re: Increased fuel consumption: issue resolved- but no logical explanation... - henrikk 2010-03-22 08:04:59 (326 views)
            • Re: Increased fuel consumption: issue resolved- but no logical explanation... - webhorn4477 2010-03-22 15:40:54 (413 views)
  • Re: Increased fuel consumption: issue resolved- but no logical explanation... - Rajaie 2010-02-28 23:36:33 (496 views)
    • Found even better mileage! - webhorn4477 2010-03-19 07:11:37 (453 views)
      • Re: Found even better mileage! - webhorn4477 2010-03-19 22:20:26 (466 views)
      • Re: Found even better mileage! - poolman 2010-03-19 12:21:20 (369 views)
        • Re: Found even better mileage! - webhorn4477 2010-03-19 22:25:57 (440 views)