First post!

I acquired a lovely R50 coupe in excellent condition with 60k miles about a year ago. If I remember correctly, it used to get over 30mpg when I first got it, but now the car doesn't get much better than 23mpg!

I've replaced the upstream O2 sensor, plugs/wires, and the air filter, but none of that seemed to have helped. What are my options from here? Replace the TMAP? Any help would be greatly appreciated!

 

No check engine light?


You might want to consider an engine oil flush to get the grime out of the piston rings to get better compression. How often do you change the oil?

 

No check engine light. Oil was changed when I first got the car and still has 10k miles left on the service indicator.

 

Don't do 15k mile oil changes or else you will ruin your motor. That's my advice that people around here don't agree with because whatever BMW says is gospel to them (however they forget that BMW is in the business of making money). /rant


Change your oil every 5 to 6k miles. These are high revving engines and you don't want to ruin the rod and main bearings. Use good synthetic oil like Mobil 1 0w-40 European Formula or better like LiquiMOLY.


Before you change the oil, get an oil flush additive and put it in with your used oil. Run the engine for a while (whatever they instruct you to do) and then change your oil.

Make sure that your spark plugs are in there tight and haven't blown out. Check this on a cold engine.

 

What are you using for fuel (octane wise)?
Power seem OK? Does it crank lots before starting or does it fire right up?
I might suggest you check to see of you have a dragging brake....
Or perhaps the change to winter fuel (which typically results in a mpg loss) with extra warm up might be the cause....still I might expect about a 4 mpg loss...so are you turning into a lead foot and driving hard? Easy to do as you get comfortable....
Any changes? Like tires or rims?

 

Using 93 octane. Car fires right up. Have not checked to see if I've got a dragging brake, will probably try that next. The mpg has been poor both during the summer and the winter. Lead foot, always, so doesn't explain the drop in mileage from before. I did change tires, but the sizing difference between new tires and old tires are something like 3% so don't think that's the issue.

 

3% rpm difference, and going to a wider tire or a highr rolling resistance perfornce tire can make a huge difference...
Stock r50 width is a 175.....
The air filter...was it an oiled one? Or a disposable?

 

Currently running 205/50-16. The stock tires on my car were 195/55-16, so not much change. I did ditch the run flat though.

Air filter is a disposable one.

 

I have a set of 16's in the 205 size.( yes 195 is stock)....so remember...you are running more rpms per mile...so the speedo is now off...about +5 mph more than before...so as much as 7 mph at highway speeds in my findings...Think I lost about 3-5 when I changed...but then do some math cause it says you traveled 3-5% MORE miles than before...So math is all messed up...
Don't think it is bad as you think...

 

I did the tire calculator and my new tire setup should be around 1.6% smaller in overall diameter.

 

More than likely tires aren't your issue.

An r50 shouldn't be doing 23mpg. My r53 in closer to stock form did 25mpg with me hooning around in it.

Something else is going on.

Get some map sensor cleaner and pull both map sensors and clean them. Be sure they go back in the right place, they are different. See if that does anything.

And yeah, change your oil every 5k. When we installed a cam in my old motor it was clean inside. 110k with maybe the last 30k getting the 5k interval.

 

Will give the map sensor cleaners a try!