CC: In our last video, we looked at diagnostic tips related to Air in our traditional conceptual framework of Air, Fuel, and Spark. This video will look at Fuel

The first thing you want to do is check your fuel trims. An air fuel ratio of 14.7 Air to Fuel is ideal for most gasoline combustion engines when they are operating in normal closed loop operation. The further you are from stoichiometry, the more likely it is that you will trigger a catalyst inefficiency code. The vehicle works to maintain that ideal air fuel ratio by adjusting the amount time (injector pulse width) that injectors spray fuel into the combustion chamber. Pollution production is minimized when you’re at stoichiometry and the efficiency of the converter at reducing that pollution is maximized when you are near stoichiometry. Make sure the converter is getting the right air fuel mixture by looking at your total fuel trims and making sure the car is running close to stoichiometry.

If you notice that you’re running rich, you’ll want to check the following things:

• Mass airflow sensor- check if that is dirty or defective.
• O2 or air fuel sensors- make sure those aren’t lazy or defective.
• Engine cooling temperature sensor- make sure that’s not defective. Perhaps it’s sending a false cold signal that causes the ECM to go rich.
• Leaking or dribbling fuel injectors- A fuel pressure leak down test can help detect this.
• Fuel pressure regulator- Again, a fuel pressure leak down test can help isolate that.
• Exhaust leaks were pinholes before the O2 sensor, look for those.

If you notice that you’re running lean, here’s some things you can check:

• Mass Air Flow Sensor could be dirty or defective.
• O2 sensors could be lazy or defective.
• Vacuum Leaks from intake gaskets or hoses.
• Clogged or dirty fuel injectors could also be an issue.
• Exhaust restrictions such as a clogged catalytic converter could also cause a leak condition.

This video is sponsored by AP Emissions Technologies.