Toyota Fuel Pump
The fuel pump needs to be able to provide fuel at sufficient pressure and volume to run the engine over a wide range of rpm’s and loads.
A check valve in the fuel pump should be able to maintain some line pressure after the engine is shut off. This reduces cranking time on restarts. It also reduces the likelihood of rough running on initial hot start-up after having sat with a hot engine for awhile. Keeping it under some pressure raises the temperature at which the gasoline boils.
In Oregon, the gasoline all has at least 10% ethanol alcohol, which lowers the boiling point. When it boils, it creates vapor pockets, which tend to make the engine start harder and then run rougher when restarted after sitting hot.
Even with everything in order, sometimes cars will have some rough running on initial hot restart for perhaps 10 to 20 seconds, especially since the gas has ethanol in it year round now. This is made worse, of course, if the fuel pump isn’t maintaining pressure to suppress the boiling.
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