Hello. Recently i have noticed a significant drop in gas milage. A half of a tank is lasing me about half of what it normaly does...

What could have cause this? very odd.

 

Bad O2 sensor.

 

What does that mean?

 

oh yeah?...

I gotta figure out how to get BMw in Montreal to use my warranty from Florida....

 

Oxygen sensor, if the ECU reads the exhaust gases wrong it may send more fuel than necessary. Replacing the oxygen sensor is somewhat cheep compared to other repairs.

However, go to Autozone and get a code scan before doing any repairs, that may give you a starting point.

 

or boost leak.

 

Did you add heavy baller chrome wheels or maybe some bad aerodynamically tuned ground effects?

 

nope

 

boost leak huh? hmmm I'll have to check and see if i have any loss...

 

tire pressure?

 

You could probably tell if it was running pig rich...

 

not tire pressure. just got new ones and they're fine

 

How can you tell if the car is running rich?

 

quarters come out the tailpipe.

 

The emissions systems are always a good place to start - O2 sensors, and all of the above. How old is the MINI? I don't know how quickly typical MINI emissions systems head south - any comments? Do you have any new mechanical mods?

 

 

Any other symptoms? Black smoke, soot in the tailpipe? Is it throwing a check-engine light? Need more information to properly diagnose.

Could easily be really hot weather combined with some stop-and-go driving. Running the ac more, combined with getting harder into the boost (to make up for the engine producing less power with hot humid air) could easily be part of it. If your mileage has dropped by HALF, though, there may be something else.

What's the data look like? Is half-a-tank lasting half the mileage, or half the TIME? If it's time, has someone else been driving your car?

Ditto the above - check boost/vacuum leaks, o2 sensor, if it's throwing a CEL get the CEL read, check tire pressure and report on your driving habits.

 

You could probably tell if it was bogging down.

 

Another thought, maybe the ECU has gone into safe mode (retards timing and runs a richer fuel map)? On certain error codes the ECU will go into this mode to allow you to get to the nearest service station. On some cars (not sure about the MINI) you may not get a permanent service light either, it'll just flash it briefly and then go into the fail safe mode. Maybe that happened at one point and you missed seeing it; running a code scan will help there.

 

Yeah I'll have to get a scane done. The service engine soon light is on aswell as the EML light.
no black smoke or anything like that. though

 

What's happening if there is soot in the tail pipe? I am not getting CEL, but I've been getting only about 20 to 22 MPG on 2005 R53

 

You can smell it if your driving behind it, there might be a little bit of soot coming out of the tailpipe, or you can try pulling the spark plugs and looking at them...they will have a lot of carbon on them.

I can also tell by the tone of the exhaust....but if you have nothing to compare it to that might be hard



Got a chuckle outta me!

If I got 20-22 on my R53...I would have been jumping for joy. Always got under 20

 

I dont get how a lot of people get such low mpg on an 05 MCS. I get about 25mpg at 71000 miles.

 

That isn't a service engine soon light, it's a get crappy mileage until you make it go out light.

 

Is it really a 50% drop in MPG ? Maybe someone is stealing your gas ?

Could just check and see when the last time was you cleaned the air filter. I have seen some dirty "re-usable type" air filters cause MPG loss. Not to your reported extent but could be a spoke in the wheel.