So I'm trying to figure out if my front o2 sensor is on it's way out. My R53 isn't really getting the mileage it should & I'm wondering if it's partially due to the aging 02 sensor. Using Dash Command, I was looking at my Long Term Fuel Trim today. While on throttle, it was consistently around +4. When off throttle / idling, it was constantly around +8. With the LTFT bouncing between these two figures, what does that mean for the health of my 02?

 

For fuel trims....
Many mods, altitude ( air pressure), and even fuel mix (ethanol) all play a roll in trim....
My suggestion....let the computer to its thing...don't over think it.
If it was extreme...maybe...
The o2 sensor that a mini uses are not wideband, but old style ones, same pre and post cat....so the computer is actually guessing a bit if it is way too rich or a bit, way too lean or a bit....could swap them out, but when it reacts too slowly, it WILL throw a code....

 

Rule of thumb: If you can add your long term and short term fuel trims together and they come to ~10% or lower you are fine.

 

Okay, so I have some updates but am now very confused about our other Mini, an 05 R53.

So, on my 06 (that I posted about before), I went ahead & swapped the sensors' positions to see if it made any difference. It did not. The car ran the same & O2 sensor read identical. Then a few days later, a CEL came up & sure enough, it was a 0030, front O2 sensor. Luckily, I'm still under 100k miles & got it replaced under warranty at the dealer yesterday. Now when I read it with Dash Command, the LT fuel trim sits at +8 at idle, and drops to exactly 0 while holding the engine at 3k RPM. The O2 sensor voltage also goes between .0 & .8 v pretty consistently, very rarely stopping anywhere in between.

Now, let's talk about our '05 R53. It's reading completely the opposite. At idle, it hangs out at around -7 & goes up to +2 while holding at 3k RPM. The voltage of the sensor is also pretty all over the place, jumping to 3 or 4 different values around .1, jump to .7, jump around a few more times, then back to .1, like its holding for much longer at the different voltage peaks. Looking like a lean condition, I replaced the fuel filter today.....no change :-/

The only difference between these two cars is that the 05 is an automatic. Shouldn't have any effect at all regarding this topic, just thought I'd throw it in. Now I'm more concerned about the '05 because these readings seem so abnormal for the R53. Would replacing the front sensor be the first step or is there something else I should check out to correct this apparent lean condition?

 

Remember, the ecu is adaptive...so it adjusts to driving style, wear, etc...

Sometimes data is just data....ignore it, and enjoy the cars. ..
Sure, you can chase ghosts all you want....

 

Really, the only reason I'm really digging into this is to try & optimize the gas mileage of both cars. Right now, the '05 is getting like 15 mpg city, which is really, really sad...