Driving With The Clutch Pressed Saves Fuel?

[andru123]

Let's say I drive down the the hill...

I press clutch and roll. Does it save fuel?

Another thing I noticed....

I drive quite fast, and see far away a red light. I release the gas pedal, the press clutch then let the car roll... until i am close at the traffic light. If it's still red, I break, if it's green I gas.

The strange thing:

When I look at the dynamic indicator of fuel consumtion (on the front panel), it shows:

- when clutch is pressed (car rolls) - ~3.5 liters/100km

- when clutch is released (braking with the engine) - 0 liters/100km

So when clutch is pressed the car consumes more fuel than when I break with the engine??? :o Or indicataor does not work properly then?

[Fidgits]

your observations are correct...

If you 'roll' your car in neutral, you are using fuel (of course you are, your engine is ticking over) but very little...

I have heard that if you leave it engaged in gear without any gas, then you use even less fuel..

[yvvan]

It is because the injectors do not work when engine braking and there is no throttle applied.

When the engine RPM is higher than +/- 1400 RPM and the throttle position sensor is at zero the ECU shuts down the injector duty cycle (no fuel injected). As soon as either the TPS is above zero (=you pressing the throttle pedal) or the engine RPM is below +/-1400 RPM the ECU resumes the injector duty cycle. When you press the clutch the engine goes to tickover which is below +/-1400 RPM, so fuel is injected.

You can test this for yourself; engine brake when engine RPM is a good bit over 1400, then blip the throttle, you will see the fuel consumption rise, same when you let it go under 1400 RPM. Allow for a second or so of lag on the screen.

Yves.