Re: The Multi Million Pound Speeding Business
Originally Posted by
OldGreyFox
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Let's suppose you were descending a hill with a low gear selected and no accelerator being used, would there still be fuel injected into the cylinders? I would assume that with today's engine management systems the fuel would have been cut off because the engine was being used for braking and still under load conditions.
I wouldn't assume that at all. If the fuel is cut off then what you are saying is that all the pistons and valves are still going up and down but with no fuel in them. That surely wouldn't be good. They are designed to have fuel in them and have the gasses expelled during that movement cycle.
Originally Posted by
OldGreyFox
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Had fuel still been injected into the engine, it would accelerate and not brake.
No. If the engine is simply working at idle speed then the accelleration is minimal. Try going into 1st gear on a flat surface, lift the clutch and stay off the accellerator. The car will either stall or slowly creep along the road.
The effort of Idle speed will make little difference going down a hill. The force of gravity will be the issue.
The entire idea of cutting fuel off whilst the engine is still running is flawed.
Stop/Start cars may well cut fuel off, but at the same time they cut the engine off too. Why don't they keep the engine running and just cut the fuel off instead ? Answer because cutting the fuel off would cut the engine off obviously.
If you had a moving car on a downward hill with engine running, ignition on and you cut off the fuel, you would essentially be putting the car into "bump" mode, the thing you do when your battery is flat, bump start.
Running your car in "bump start" mode for any significant period of time isn't going to do it any good imo.