Dear All,
Just noticed, that on my Benz I am getting 7,01% long time fuel trim on bank 0; 7,81% long time fuel trim on bank 1, and in the same time both short time fuel trims are zero.
Does this mean anything (bad)? Do I have to worry about the long-time trim being 7% off? Why can it be that off?
In general the car and the engine both seem to be running fine, apart from the issues I am still getting with hot starts which take two (max. 3) attempts each.
Mercedes-Benz ML 55 AMG 2001 w163 5,5l V8, no turbo, automatic, VIN: WDC1631741A297248, 243kkm
Picture of a typical ML 55 AMG: https://1drv.ms/u/s!Alv3RQPn1ylAqE8bjbgqS9nj_mgh
Thanks a lot in advance.
Does this mean anything (bad)?
It means the computer detected that the air/fuel mixture is too lean. Positive numbers indicate the computer is trying to add more fuel.
Do I have to worry about the long-time trim being 7% off?
"long term"
Yeah it's high enough that you should start thinking about fixing it. Obviously it hurts your fuel efficiency, and over time it will wear out your catalytic converter. The engine will run a little hotter which isn't good for it. If it continues to get worse, you will get a check engine light.
Why can it be that off?
Lean mixture means too much air and/or too little fuel. There are several things that cause this.
- unmetered air entering the engine (vacuum leak)
- malfunctioning fuel injectors
- poor fuel pressure
- malfunctioning MAF sensor
- exhaust leaks
- etc....
You may want to start with some fuel injector cleaner in your gas tank. That might get you a few percentage points back.
Scotty has videos about all this stuff.
Many thanks, also for the terminology corrections!
Tons of reasons for running lean, too bad 🙁
But if in the long-term the fuel-to-air ratio is 7% off, how can this ratio be always perfect (0%) in the short-term ? Or is the STFT being indicated / calculated around the existing LTFT?
Tried it with some soft Liqui Moly injection cleaner before. Will try it with a better / more efficiant one in the coming days, and before I do, I will definitely watch some dedicated Scotty´s videos first.
Thanks again for the detailed reply!
Very enlightening vids! I cannot thank you enough.
When it will get warm, I will start my attempts to isolate the root cause, hoping that my doitmyselfing capabilities will suffice for that.