Hi everyone,

I've been doing some datalogging recently and I've come to find out that I seem to have weird issues with the short term fuel trims (STFTs). Most of the time while driving, they (both bank 1 and bank 2) are stuck at a specific number, generally 0.90-0.93 or so. While this is occurring, the front O2 sensors on both banks are reading consistently rich (0.85+) and do not fluctuate like they should from 0.00 to 0.90 to 0.00 and so on. The O2 readings however are not stuck, they do vary normally (as you can see in the 2nd graph below) but don't go below 0.85 generally.

On a rare occasion while driving, the STFTs will start working like normal and will constantly fluctuate around 1.00 like they should - at this time, the O2 sensor voltage readings fluctuate also like they should.

I looked back at old datalogging I did and found out that this was happening literally as long as 5 years ago, so it isn't a new problem. It runs fine but it still seems to be a problem in that it results in running rich.

Here is the STFT bank 1 reading from the other day during a drive - it is stuck for most of the drive but starts working correctly around 1167 seconds and at 1271 seconds goes back to a set number.


Here is the O2 sensor voltage bank 1 from the same log


Does anyone have any ideas?
Thank you

 

Hello and welcome aboard! Does by any chance your Mustang have an aftermarket calibration tune? If it does, you may want to consider informing your tuning specialist about the STFT's in the data log as running rich.. More than likely, its due from your air/fuel ratio or spark and timing curve trims not being dialed-in.. Also have the tuning shop look over your data logs as well.. If on the other hand, your running the factory calibration tune? you may want to consider having your local Ford dealer's service department run a diagnostic system test in regards to the STFT's... Meanwhile. wish you nothing but the very best of luck in getting your STFT issues fully resolved ASAP.