I'm doing the same thing as push-jump start!

I'm trying some tips mentioned by these hyper-milers. One of them is to turn off the engine while approaching the intersection with traffic light on red. Sometimes due to the distance, I lost the power to brake. So I tried using the 2nd gear to slow down the car. (Note: I only do this with enough distance between cars, or I would rather turning the engine back on.) A few times I found the power gets back up again. Initially, I was wondering if I did turn off the engine and then realized that this is the same as push-jump start a car.

So how does it work? Why would the engine start up again without involving the starter?

Thanks,

Reply to
liu
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Because you're spinning the engine with the clutch instead of the starter motor.

I'm finding myself asking, "Is this a trick question?"

All the starter does is spin the crankshaft via the flywheel to build compression in the cylinders and getting the fuel to ignite. You're using the transmission instead of the starter motor.

I am going to refrain from calling this dumb, let's just say it's dangerous. For one thing, it puts a lot of wear on the clutch, and if you're managing to do this with an automatic, I think a call to AAMCO will soon be in order.

For another thing, you've already found out you've lost some braking power. God forbid a kid jumps his bike off the curb while you're trying to save a few pennies on gas. Steering goes out, as well. making the thing handle like a loaded garbage scow.

Leave the car on. It's dangerous, and, in most states, illegal. Hell, in most states it's illegal to put the trans in neutral and coast.

I'm praying you don't kill somone, at least other than yourself.

Reply to
Hachiroku $B%O%A%m%/(B

If the car is in gear you are not really coasting. You need to keep on the gas a longer distance before starting your deceleration, because the car will decelerate at a higher rate when you are turning the engine over. Therefore you are not saving as much gas as when you coast with engine out of gear.

BTW, some of what hypermilers say works, other things do not work. Mixed bag- depends on who says it. Coasting out of gear does work, playing lights works even better (though playing and coasting are not mutually exclusive.

Reply to
Don Stauffer

"coasting" in gear saves gas because the engine computer will cut off fuel delivery. coasting in neutral will not - the computer needs to inject to keep the engine rotating, something provided by the drive train if in gear.

Reply to
jim beam

Thanks for the response. That's the answer I'm looking for.

Yes, it can be dangerous. I won't tell anyone I know to do that. I did that a couple of times when no car in front of me. BTW, I found the brake is fully functioning within 10 to 20 seconds after turning off the engine.

Reply to
liu

Thank you all for the advice. My car is manual transmission. I keep it in neutral when coasting. Judging by the RPM. coasting in neutral requires less gas than in gear. It also travel longer distance too.

Reply to
liu

it travels a longer distance, but only coasting in gear shuts fuel delivery off - the engine computer is programmed that way. it /has/ to keep on injecting fuel while in neutral or the engine will stall. rpm is not an indicator of fuel consumption.

Reply to
jim beam

Does this apply only to newer cars? Mine is 1994. If you have any URL info on this, please provide. I'd like to learn more. THANKS!

Reply to
liu

Glad to oblige! ;)

Reply to
Hachiroku $B%O%A%m%/(B

Coasting a longer distance still saves fuel even if idle fuel is not cut off. If you travel a shorter distance, that means there is an additional distance before coasting that you are traveling with cruise throttle and fuel flow that you would NOT be traveling with the longer coasting distance.

Reply to
Don Stauffer

it applies to all electronically fuel injected cars. modern cars are more aggressive in their cut-off strategy than older ones, for instance, older ones cut off when the throttle is closed and rpm's are above about

1500, but modern ones look at more than engine rpm to determine whether to inject and will cut off fuel in pretty much any over-run situation.

if you want an example, megasquirt is a d.i.y. injection system that the consumer can program. if you want, you can dig out the computer code and read it yourself. more accessible though is the over-run setting which is discussed here:

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Reply to
jim beam

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