Good day everyone. I have a 2010 r56....just turned 100,000 on the odo. When i first got this a year ago, i swapped out the spark plugs for new iridiums then i changed the 4 coils around 5 months ago. Mileage was great. Then about 2 weeks ago, I notice that the average fuel consumption gauge ( see pic ) was counting down MUCH FASTER now....whereas before it slowly ticked down as you used your gas. What's odd is that it will do it no matter if i am driving fast or slow....incline or flat. Does it on the freeway and on 30mph city streets where i'm going under 30. It will then COUNT UP up to about 7 or 8 miles, stay there for a while, then slowly ( or quickly again ) tick back down. If this is how it was behaving all along, then this is the first time i have noticed this behavior.

Also, my dash threw a CEL....diagnotic showed P0128 - coolant temperature sensor. Went to napa auto, got a new one, then replaced the bad sensor. Easier than I thought. CEL went away and no more fault codes. However, gas consumption ( as far as i can tell ) remains the same with the same symptoms. I found the following list of probables on a site:

Sluggish Oxygen Sensors
Inaccurate or Defective Coolant Sensor
Defective Engine Thermostat
Engine Misfire
Intake Manifold or EGR Valve Leak
Worn or Fouled Spark Plugs
Dirty Fuel Injectors
Low Compression
Wrong Oil Viscosity
Dirty Air Filter
Clogged Converter or Exhaust Restriction
Slipping Clutch or Transmission
Low Tires
Dragging Brakes
Too Much Weight in Your Trunk
Poor Driving Habits

i know for a fact that it is not tires, my driving, tranny or clutch, brakes, oil viscosity, or spark plugs.

What i DO know is that i would sometimes feel a sort of misfire although i have never gotten a CEL for it. I'm inclined to think fuel injectors, O2 sensor, EGR, or thermostat. Any ideas? My r56 pulls hard though. no sluggishness at all.





Also, there are 10 hash marks on the fuel gauge. How many gallons does one represent?

 

No other codes?

What is your average MPG over a tank of gas? Has it changed?

The "range to empty" is an estimate based on fuel level and short term average mpg. It will go down if you're in stop and go traffic or driving hard, and go up if you're cruising on the highway. Look at the actual range you get out of a tank of gas and the long term average mpg for a more accurate measure. It's possible that the fuel level sender is getting wonky, but not likely.

The fuel level gauge (or "carrots") is very non-linear. I reset my trip odometer every time I fill up, I get to about 85 miles before the first one goes off, then 125 for the second. I'll show "half a tank" (5 on, 5 off) at about 300 miles which I know is BS because I typically get about 420 miles on a tank.

 

the secondary 02 sensor is responsible for fuel trim


*if your mileage suddenly took a *****.. then its the likely culprit (with no other symptoms)

 

Was kinda thinking it might be that.....is that the one on the front next to the turbo?

 

nope..it underneath at the bottom of the DP. Just lift the car..its right there.

 

Was just reading an article about replacing the downstream one...and yeah....the pictures show where the plug is as well as how to get to the sensor itself. Hoping this is the solution. Thanks bro!

 

So I replaced the thermostat sensor. Looks like it is working fine. I then decided to change the downstream O2 sensor since it COULD be the cause and since my car just passed 100,000 miles - and the sensor should be replaced anyway. The old one looks like a pigeon got to it from within the combustion chamber.

Anyway....no fault codes showing up EXCEPT that the fuel consumption is still on the high side IE nothing's changed. The P0128 CEL did come up a couple of times again which leads me to think that the problem might be the Thermostat ( housing ) itself. Right before I got the car, the dealer said it had replaced the unit. I'm betting that they didn't get a genuine mini part for it.

So thermostat housing next? Could that solve this issue once and for all?

 

Of course, and why not? I'm reading more and more different information about cars and engines on the Internet. This industry is developing very quickly. Now you can even predict some things, referring to the facts that you can read all on the same Internet. So I recently bought a new Porsche and wanted to see how you can reduce fuel consumption on this car. I decided to Google and came across one site and found out that if you change the settings in the vehicle, the fuel consumption will be lower. I didn't even know about it. It's certainly fascinating. Good luck and good cars to all!

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