How to use fuel trims and downstream O2s to analyze intermittent misfire concerns, according to Search Auto Parts.
Let me share with you a technique that will give you a quick and effective way to capture the concern and determine, with a high level of certainty, an analysis path. It uses your scan tool to watch the fuel trims and the downstream O2 sensors. I began teaching this technique to Ford technicians in the Advanced Drivability courses starting in 2000 as a Service Training Instructor with Ford Motor Company.
To understand why this method works, let’s lay the foundation by reviewing Powertrain Control Module (PCM) feedback fuel control.