Subject: Found even better mileage! Author: webhorn4477 : member since November, 2009 : 45 posts Posted on: 2010-03-19 07:11:37

While browsing through the stack of BMW-parts in my basement, looking for some parts i bought for my E30 325i convertible which is "in the works" now, i came across the pair of old pre-cat O2-sensors i took out of my E39 530i and replaced with new ones some 30,000 mls ago, long before the vanos fix. I did replace these not because they were defective, but in an effort to "make everything perfect" around the engine.

What i had completely forgotten about: the new sonsors i had been putting in, were universal post-cat sensors. Though beeing the exact same type of sensor (Bosch LSH 25) and thus having the same characteristics, they have a differently shaped metal protection around the sensor tip where it is in the exhaust gas stream.

I had been doing so because i didn´t want to pay the ridiculously high price for the OEM-sensors and was able to get these universals for quite cheap back then. Every "expert" i spoke to about this, said that it should not be a problem, as long as the sensor type is exactly the same, which it is. I then attached an oem connector to them and everything was fine- as fine as can be with worn vanos seals. I was left with a feeling that the different shape of the sensor tip protection must be there for a reason, though.

When finding the old sensors, this came back in my mind and, since changing the pre-cat O2-sensors on these engines is only a ten-minute-job, i swapped them out for a test. The results were astonishing: the very tiny bit of uneven accelleration at low rev´s that i still had left after the vanos repair, is now completely gone, and the fuel consumption has dropped dramatically- now for the first time it is clearly a lot better than before the vanos change- by about 1 litre/100 km, when it had been about 0.2 litres/100 km before. I´m a happy camper now :-)

The reason must be the different shape of the tip protector. Judging by their shape, the oem pre-cat sensors allow a better flow of exhaust gas around the sensor tip behind the protection. This does enable the sensor to react a lot faster and thus measure more precisely. This quality is not needed on post-cat sensors, since their main purpose is to monitor cat efficiency.

So, it should be no problem using any kind of Bosch LSH 25 O2-sensor in the pre-cat position on the M52TU and M54, as long as the sensor tip protection is shaped like on the OEM ones.


Just wanted to tell you about my findings,

webhorn

• Increased fuel consumption: issue resolved- but no logical explanation... - webhorn4477 2010-02-28 19:02:13 (798 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 (444 views)
        • Re: Increased fuel consumption: issue resolved- but no logical explanation... - webhorn4477 2010-03-17 18:51:08 (376 views)
          • Re: Increased fuel consumption: issue resolved- but no logical explanation... - henrikk 2010-03-22 08:04:59 (325 views)
            • Re: Increased fuel consumption: issue resolved- but no logical explanation... - webhorn4477 2010-03-22 15:40:54 (412 views)
  • Re: Increased fuel consumption: issue resolved- but no logical explanation... - Rajaie 2010-02-28 23:36:33 (495 views)
    • Found even better mileage! - webhorn4477 2010-03-19 07:11:37 (452 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 (439 views)