Good Morning MCF Family!
I have the OBD Torque II in my phone. It works great although I wish it would do ABS and Trans codes.
My question "Today" is about Fuel Trim.
What is it?
What is it telling me about my cars operation?

Until now I have only had the need to use a scanner to check and clear codes. Now I want to understand EVERYTHING the scanner tells me.
Educate me! Please?

 

Long Term or Short Term?

It's telling you whether the car is adding or removing fuel to hit the 14.6 mark using your sensors and PCM.

 

Fuel trims are crazy important, I always look at them first when scanning a vehicle. It shows how the engine is running lean or rich and how the ecm is controlling it. 0 to +10/-10 is ok more than that you have an issue, vacuum leak, injector problem, o2 sensor issue. Fixed many drivability problems with watching fuel trims.

 

Thanks Admin Mike! I'm not sure about long or short term. To be Honest, I had never heard of Fuel Trim until I started checking out all the functions in my Torque app.
Is the 14.6 the optimal Air/Fuel ratio?

I'm sorry, I have a feeling that each answer I get is going to generate more questions.
(The wheels in my Geek Brain start turning when new info is added)

 

14.6 is optimal for oem fuel efficient daily drivers. Max Performance is 12.5-13.0.

 

Depends on the applications. 14.6 is stoich AFR. That means that theoretically you should be burning all of the fuel and oxygen efficiently.

Typically for an NA car you can increase timing and add some fueling to run around 12.5 because running slightly richer is better.

I'm shooting around 11.0 on my CSC build.

Find out if the Torque app is trying to look at Long Term (LTFT) or short term (STFT).

If it's LTFT and running around -5% - 0% your car is running pretty well. If it's in the positives, you are running lean and that's not great.

 

What great info guys... Thank you... JC, I too have iobd2 on my iPhone 5s and S4 android... I have often wondered what it is trying to tell me... Thanks again,

 

LTFT is important - it helps diagnose all kinds of issues. Mine usually runs between -2 and +2. STFT shows what's happening right now (will change when you hit brakes, or accelerator). The closer to 0 it is at idle, the better shape you're in.

 

Wow this is Great. I'm sure I will have more questions. Gotta file this stuff in my Noodle and Swish it around a bit so it Stays Put!
Thanks everyone for all the great input.
Damien, your welcome! It's better to get this info here. We explain thing to each other in a language we can all Understand. It's called "Shade Tree", "Wrench or Ratchet" head, depending on what part of the planet you are from!

 

Just to clarify for the OP, the 12.5 and 11.0 numbers are in PE mode (ie heavy load conditions like WOT, going up a steep incline under heavy throttle, etc). Normal fueling for idle and light throttle should be up around 14.7 otherwise you'd be wasting a lot of gas.