Another Poor MPG thread 3.0 6MT

[tecboy99]

Hey All, recently I've been noticing some pretty low mileage. (Around 15 mixed with more highway than city.) When checking my fuel trims, I noticed that the long term trims are hovering around +11%. According to BMW, anything 8% or above is a problem that should be looked into. I replaced the lower intake boot last year, and the CCV this summer. I do have a shadow code saying there is a short to ground in both precat banks that I can't seem to get rid of. But there the sensors are indeed giving a reading. The car has 161K on it, and I'm thinking it's probably time for new sensors. What do you guys think?

[IMG]Screen Shot 2016-12-20 at 5.50.10 PM by tecboy99, on Flickr[/IMG]

[upallnight]

Smoke the engine and find out where you have a vacuum leak.

[X53Jay4.8is]

Originally Posted by upallnight

Smoke the engine and find out where you have a vacuum leak.

Very sound advice and great way to identify a problem.

[Ricky Bobby]

The fuel in Minnesota is probably horrendous this time of year - winter driving always drops the mpgs a bit for me - then there is your 20" meats which contributes -

Fuel filter replacement and air filter cleaning helped me by about 1 mpg this year -

[tecboy99]

Originally Posted by Ricky Bobby

The fuel in Minnesota is probably horrendous this time of year - winter driving always drops the mpgs a bit for me - then there is your 20" meats which contributes -

Fuel filter replacement and air filter cleaning helped me by about 1 mpg this year -

Yeah, the gas probably isn't doing my any favors. I replaced the fuel filter this past summer, and the air filter last month. I also don't run my 87's in the winter. I have a set of 18's with blizzaks. I'm replacing the o2 sensors this week as preventative maintenance. If that doesn't help, I'm going to smoke test it after hours at the dealer.

[Ricky Bobby]

Hmmm yeah if on 18s that sounds a bit low - let us know your findings, the o2's might be past their life -

[iansanderson]

I average around 15 MPG in the winter as well with my 04 6MT. No codes, no leaks. Your multiplicative values are both high, but with no SES light or codes, everything is technically within spec. I would definitely do the O2 sensors. BMW recommends 100K for replacement. Check the NTK sensors on Amazon. Worked great on my E36.

[upallnight]

Originally Posted by iansanderson

I average around 15 MPG in the winter as well with my 04 6MT. No codes, no leaks. Your multiplicative values are both high, but with no SES light or codes, everything is technically within spec. I would definitely do the O2 sensors. BMW recommends 100K for replacement. Check the NTK sensors on Amazon. Worked great on my E36.

OMG!!!! BMW actually recommends replacing parts???? I thought everything such as ATF was lifetime.

[iansanderson]

Originally Posted by upallnight

OMG!!!! BMW actually recommends replacing parts???? I thought everything such as ATF was lifetime.

It's all marketing. Oddly, BMW now moved brake fluid flushes to 3 years I would assume to save money on maintenance plan brake flushes that come with new cars.

[richardb]

I saw a nice improvement in MPG with replacement of the pre-cat 02 sensors. Definitely recommend if yours have very high miles. Keep tires inflated properly as well. Does your car warm up quickly or very slowly? We have notably poor fuel mileage from a stuck-open thermostat, it takes almost 20 min to warm up vs. 7.5 min on our 530i.

Here's a DIY for that pre-cat sensors I uploaded a while back: