Hey Scotty! 2010 Acura RL with 111K miles. I drive mostly in the city and was getting about 15.3 MPG in the summer, but now getting about 14.6MPG. Decided to see a live data using the scan tool and noticed STFT to be from +5 to 6% and LTFT +2 to 3% at idle. Clean new stock Honda filter installed, MAF was recently cleaned with CRC MAF cleaner. Throttle body is clean, all hoses seem to be soft, tight and in good shape. When I give it a bit of gas, STFT goes down some and may get closer to 0 and while driving LTFT may lower a bit too. I always use premium gas(tried different gas stations too) as it is required. Any ideas?
I don't know why you're complaining about those values, they're good! That's where you want your STFT and LTFT to be. Normal range is -10% to +10% where 0% is dead perfect. Negative fuel trim means that fuel is being subtracted to correct rich mixtures, and positive fuel trim means that fuel is being added to correct lean mixtures.
@razmigb
Just wanted a better MPG and that is where the idea with scan tool came into play. Thank you for the input or should I say Շնորհակալություն
Aye, no problem! Fuel economy is just one of those things that gets worse as the engine ages. It could be from carbon build-up inside the engine, dirty fuel injectors or fuel system, or even the spark plugs being old and need replacing. When were your plugs changed last?Maybe try putting a bottle of Techron fuel system cleaner in the tank first. It's a great fuel system cleaner that actually works; I've used it for years.
@razmigb
I looked at the engine, at least opened the oil cap and used flash light to see and it seems pretty clean. Oil was always changed every 6 months or when maintenance minder would tell. Timing belt, water pump, spark plugs were done about 6k miles ago. I did use couple of different fuel cleaners such as red line( I think) and also tried at some point Liqui Moly. No change to MPG. The interesting thing is that I did try to take it for about 40 min drive on a freeway and did get at least 22.7MPG, which seems to be accurate to the manufacturer's ratings. For city, they advertise up to 16, but in fine print, it mentions from 13 to 17. The tires are Micheline Pilot Sport 3 A/S(UHP) but initially the car came with Micheline Primacy MXV4 and these were Grand Touring.
Gear advices from @Razmigb.
To add a little comment, it is normal that you get a bit worse mpg in the winter time.
@yaser
So I guess we will wait till days warm up, thanks!
@yaser
Good point actually. Engine needs to run rich a little longer during the winter to get it warmed up.
Seeing STFT going lower at higher rpms would make me suspect a vacuum leak.
Wouldn't hurt to spray come carb cleaner around your vacuum lines, connections, intake manifold (gasket) and around the motor-side of the throttle body while it's idling.
Just use "little bursts" of the carb cleaner aimed closely at specific areas and listen for idle changes.
We live in a litigious society so I feel compelled to provide a warning that anyone with half a brain should already know:
Carb Cleaner Is Flammable. Keep a fire extinguisher close at hand and maybe don't do this in your garage.
Even though those STFTs aren't "out of spec", they're getting very close and the way they're going down at higher rpms,
if it were me, I'd be looking for a vacuum leak
@jack62
I looked at the car for a brief moment that I had, removed the "beauty cover" and checked tubes by visual inspection and by touch. All of them look like new, clean and rubber feels soft depending on the hose. If hoses came with clamps on each side, then they still have exact factory color markings on them. The engine was hot, so I couldn't stick my hands under the throttle body, as there were couple of hoses, but looked good. The only thing I am unsure about intake manifold. Do you know if in my vehicle the intake manifold is behind the engine, kind of towards the firewall?
Also I looked at the PCV valve which was on the right side of the engine and it has a breather hole I guess? Maybe that valve causing STFT to be in the positive?