Understanding Fuel Trims

Understanding Fuel Trims

The fuel trims are what govern what's going on inside the engine. This video is sponsored by Auto Value and Bumper to Bumper.

CC:

Let’s take a trip. It’s 1974. You’re in Denver, Colorado. You’re in your car that has a carburetor, and you’re getting ready to go over those rocky mountains to go to California. You’ve noticed that you’re halfway up the mountain, the engine’s starting to struggle. You go a little bit further. You notice that you start misfiring and the plugs are fouled. So what’s going on here? Well, essentially with this, you have the blue, which represents oxygen, and the red represents fuel, and this is the perfect ratio. But you’re taking away this oxygen, and when you take away the oxygen, you should take away the fuel. Carburetor can’t do that because it has fixed jets, and the metering stays constant no matter what altitude you’re at. This is why certain shops in Colorado specialized in carburetor tuning. Let’s fast forward 50 years, and you’re in a modern vehicle.

You’re in Denver, Colorado. Same situation with this. The fuel trims are what govern what’s going on inside the engine. So as that air density changes and the amount of oxygen entering the vehicle goes down, again, it’s able to then take the fuel and reduce that. So let’s say you make it to California, you’re on the west coast, and the air density is even higher. If you head to the carburetor vehicle and you had it tuned in Colorado, it might be a little at tuned, but with modern vehicles, they’re able to adjust the fuel trim and add a little fuel so the engine runs better and has lower emissions. So what is a fuel trim? There’s two kinds. Short term and long term. Short term is in the moment what’s going on right now in the engine, a long term that indicates overall health of the engine and how much it’s adjusting for the changes in oxygen levels. With this, it’s able to adjust to make sure that the engine’s running properly so you can make it over that mountain. I’m Andrew Markel. Thank you very much.

This video is sponsored by Auto Value and Bumper to Bumper.

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