Long term fuel trim 2016 Toyota Tacoma 3.5

Question

Hey everyone, my truck has a warning light stating maintenance is required, and I think it’s just that the mechanic didn’t reset something when he did my oil check, but I decided to hook up my scan tool to see if I could do so, and couldn’t.
Anyway, I checked out the other data and noticed my LTFT was -3.9ish and if I remember correctly that means it’s running rich(?). This was on bank 2, bank 1 was 0.0. Just wondering if maybe I need new injectors, or if it could be something more serious. I’ll take it to a mechanic when I get a chance but wanted some insight first.

thanks!

jack62 · Accepted Answer

Remember , the fuel correction is the total of STFT and LTFT. If you had -3.9 LTFT and +3.9 STFT (=0) then the computer wouldn't be correcting the fuel mixture at all. Given enough time the LTFT would get pulled up to 0 and the STFT would get pulled down to 0.

You want to look at both.

Also, you want to look at them at idle and then after holding the rpms at around 2500 for a couple of minutes to see if the rpms have an affect on the fuel trims.

Even though you're only seeing the rich condition on 1 cylinder bank you still need to see what the ECT sensor is reading. An ECT sensor that's reading lower than the actual ECT (temp) will trick the computer into thinking the engine is colder than it actually is so it will add more fuel.

But the upstream O2 sensor will pick up that rich condition and you'll get negative fuel trims.

Same goes for the MAF (or Map sensor). You want to look at the MAF sensor to make sure (in your case) that it's reading around 3.5 g/s at idle.

Combined STFT + LTFT on a cylinder bank that's under 5% (either positive or negative) is acceptable and perfectly within the computer's ability to correct the air/fuel mixture and most people don't even worry about it. You're into the (fine tuning area).

Remember, that #2 cylinder bank isn't actually "running rich". The computer is correcting the rich condition by subtracting 3.9% of the fuel. It would be running rich and possibly creating a problem if the computer wasn't doing that.

However, I'm like you. I'd want to nail down why it's happening.

But a 5 year old Toyota Tacoma having a sticking/leaking fuel injector would be way down on the bottom of the list with the last things I'd suspect.