As many of you know, we host a monthly contest sponsored by our friends at Federated Auto Parts. It's our "ASE Question of the Month" and we try to match it to the "theme" of our monthly issue. For August, our question was:
Technician A says the ECM's primary role in engine management is to ensure that the feed gasses being passed along to the catalytic converter are maintained in a very narrow range. Technician B says that the fuel trim data PIDs (Parameter Identifiers) represent corrections made to the injector "on time", expressed as a percentage. Who is correct?
You’re correct if you said that both technicians were right!
The exhaust gasses leaving the engine and entering the catalytic converter are also referred to as "feed" gasses. In order for the converter to be able to do its job, these gasses must be very close to "lambda" as possible - within 0.995 to 1.005! So Technician A is correct.
Technician B is also correct. The numbers you see on your scan tool represent percentage adjustments to the base pulse width calculation. Short Term Fuel Trim is an addition to, while Long Term Fuel Trim is a correction factored in as part of a modified base calculation.
Correct or not, everyone that answers the monthly question has the option to enter our random prize drawing. The prize is a collectible diecast that is great for displaying at home or in the shop! Want to be our September winner?
