German Auto Repair in Eugene

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Difference between fuel types

Fuels, regular vs. premium

One of the questions I’m asked a lot is can you use regular in a vehicle that was designed for premium. The short answer is no.

The engineers that design the engines and all the controls for it are very careful with the timing of what is called the power stroke.

Years ago, when you could tune engines, one of the critical adjustments was ignition timing. Ignition timing as most other “tuning” adjustments are no longer adjustable. Yes, don’t ask for your car to be tuned anymore, it’s a word of the past with newer cars.

To understand ignition timing, picture swinging a kid on a swing. The timing of pushing the kid is important, if you push too late, you are just pushing air (late timing or retarded timing) If you push the kid to early, you will slap his back or maybe push the kid out of the swing, not good. The perfect timing for the kid on the swing is to push him gentle in the beginning or the forward stroke and continue it until the kid is at the top of the swing.

The same for the power stroke of a piston, if it happens too early, the engine “pings” like slapping the kid on the back. It will damage an engine.

One of the differences between regular and premium is what is called octane. The higher the octane, the “more controlled” it burns. Premium fuel burns slower and more controlled and is needed in higher performance engines.

Newer vehicles have a lot of sensors used to control the engine ignition and fuel mixture. Most have what is called a knock sensor, it listens for the engine to ping and if it hears it, the ignition timing will be retarded until it doesn’t hear it anymore. But this control has only a small amount of leeway to go before it can’t adjust the engine timing 


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