STFT FUEL TRIMS - Explained what you need to know and Tuning info

Basically explained this is engine Rich/Lean o2 correction from the O2 sensors  

Do you have a smell ? Poor MPG and a constant misfire and shake while driving 

Many people now watching TV and becoming more familiar with tuning Lingo talk about individual cylinder tuning with Timing or fuel Neither is available with the stock ECM. 

There is no reason for it to be 8-25+% off side to side when you get those results watching fuel trims there is a Mechanical issue This is not something we can tune out 

Issues include 

  • Ignition misfires caused by fouled spark plug, weak ignition coil or bad spark plug wires.
  • Defective oxygen sensor or its wiring
  • Air or vacuum leaks in the intake manifold, throttle body or in a vacuum hose.
  • Clogged or unresponsive fuel injectors
  • Air getting into the exhaust manifold through a crack or gasket leak
  • Malfunctioning MAF (Mass Airflow) sensor


When you Start Your vehicle it runs in what's called Open loop - Its running on the ECM tune with the basic sensors being used to start and warm up - Once it reaches 120 range it goes to Closed loop -

In a closed-loop system, an oxygen sensor, along the exhaust path, measures the oxygen to provide feedback regarding the air/fuel mixture and automatically adjusts the amount of fuel required for starting. As the engine temperature rises, sensors provide output to adjust the air/fuel for running

We as tuners can make changes based on the STFT to adjust air fuel Rich/Lean with datalogging and to compensate for Camshaft, injectors and Air intake changes. for a +/- swing 

We cannot adjust fuel side to side ( Bank 1 vs Bank 2 ) with Hptuners - so the same amount of fuel is injector in Cylinder 1 as it as cylinder 8.