[Darren1231]

So lately I have been getting god awful MPG's. I have ran high octane gas in her and driven her pretty hard tryin to break out any build up but no luck. I'm afraid to Cfoam or put any other cleaning product in her but I think I might replace my O2 sensors. However if there were bad wouldn't I be throwing codes? Maybe I need a new air filter... What's your take?

 

[mio_e46]

Me too, anyone please share! Thx

 

[doru]

• Check for very small vac leaks
• If O2 sensors more than 100k, change them
• MAF gets lazy after 100 k as well
• Clean fuel system (fuel filter W. regulator), injectors
• Air filter
• Check DISA for functionality
• Clean TB and ICV
• Go easy on the gas pedal
• Avoid stop-and-go traffic if you can

 

[Darren1231]

Lol Moving into the city is when it stated to get really bad. Stop and go daily. But where I was getting close to 500 mi to the tank, I'm now getting 200.

 

[edjack]

Stored P-codes? Monitor short-term and long-term fuel trim, via a scan tool. Both s/b in the range of +/-5%. If both are positive, and more than 5%, there are vacuum leaks downstream of the MAF.

Consider the list from doru. Report back.

 

[Darren1231]

Stored P-codes? Monitor short-term and long-term fuel trim. Both s/b in the range of +/-5%. Report back.

Dumb that down or elaborate and I just might... Lol

 

[Darren1231]

Wait are you talking about air to fuel ratios?

 

[edjack]

The fuel trim numbers indicate the adjustment rerquired by the engine computer to keep the engine at the proper air/fuel ratio, about 14.7:1.

The short term fuel trim is an instantaneous value, based on engine load. The long term fuel trim is used to "zero out" the STFT after a period of adjustment of STFT.

As I stated, these numbers can offer clues as to what's happening. If you do not have, or are uncomfortable with, a scan tool, you'll need to find a savvy BMW indie to troubleshoot this issue.