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Ford F150 - What are short and long fuel trims?

I have a 1998 F150 w/5.4L. What are the short and long fuel trims? The readings are between 50-98%. Where are they generated from?
Answer:

Fuel trim is the term used to indicate the amount of fuel being cut back by your Ford's ECU in order to maintain as close to a 14.7 to 1 air to fuel ratio. The higher the percentage of fuel trim the harder the computer is trying to adjust fuel. Short term fuel are immediate corrections being made as your vehicle is running. Long term fuel trim are adjustments being made every 15 minutes. Ideally you want long term fuel trim at zero (0) percent, and short turn switching up or down not more than 3 to 4 percent. Any fuel trim greater than these amounts indicate a rich fuel problem and will require diagnosis. Rich fuel simply means more fuel is getting to the combustion chambers than needed. posted by SmogTips Support

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