my question is...if you have an automatic, then why the f*ck would you go out of your way to throw it into nuetral? why? do you want a manual that bad that you have to shift from nuetral to drive in your automatic?

 

A manual transmission vehicle uses zero gas while coasting downhill. Zero injector pulsewidth = zero gasoline consumption.

You get the "loud exhaust note" because air is still moving through the eninge but it is NOT being ignited. The engine doesn't stall because it can't - it's being kept spinning by the vehicle's momentum. As the engine gets closer to idle, or below a certain cutoff rpm (usually 1500ish depending on the vehicle/manufacturer), it starts spraying fuel again.

I've tuned a lot of manual transmission vehicles. I'm not making this stuff up out of thin air.

 

I'm still not buying this. The ignite is what makes sound. Take away that, and it would be more like an air compressor....Like i siad before.....If you have loud exhaust on your car truck, and you downshift to coast....you still hear the igniting of the fuel/air. if it didnt ignite, it would be quiet. There may be a few vehicles out there that do it....but not any i drive/ seen

 

From what i understand now after reading about this. Some cars used to turn injectors off while coasting but they stopped doing that when OBDII came into play. Something to do with the Cat losing temp and then not working correctly.

 

I can't seem to wrap my head around this. If it turned off the injectors it should sound like a diesel rig (aside from being a much smaller engine) which would cause the engine to slow down.

 

Ditto. Not only have I been driving standards for about the same amount of time, but I've put my manual in neutral while coasting downhill countless times too. Its almost a habit now. I've never heard that doing this was bad for the engine. O.o

 

You can find various results by Googling, but the SRT-4 folks have already discussed it pretty well. Looks like I'm not looney just yet:

http://www.srtforums.com/forums/f10/...asting-361496/

 

The quote on that site says "momentarily turn off the injectors". In computer terms, momentarily can mean 100th of a second. But regardless, it can't be for any significant amount of time or the engine would stall. No fuel means no spark/ignition which means no running engine.

John M I'm not saying you're wrong, by that quote you are very correct, and I'll conceed to that, but even if I'm wrong, because of personal experience, no one will ever convince me that coasting in neutral is hard on your engine or tranny, and harder on fuel.

 

THe engine is running on all eight cy when coasting in N. If the engine was not running, you would lose P.S and P.B, with my 2500 hemi, the rpms don't drop past 1000 Rpm when coasting ...

 

If coasting in neutral, it is indeed firing to maintain idle. Also, like you said, it actually keeps rpms slightly above idle to make sure there is vacuum available for brake assist.

Exactly! When you coast in gear, the engine technically is NOT running! It's being kept spinning by the vehicle's momentum.

If you're coasting in gear (zero throttle input), over a certain rpm (depends on vehicle), it will cease any and all fuel injection until the rpm goes below that point or when the throttle is pressed. Fuel injection makes this transfer seamless. It'd never work on a carb, and actually I'm not 100% sure if TBI vehicles do it that way.

You're also correct in that coasting in neutral is not hard on a manual transmission vehicle. The difference between fuel to maintain idle and zero is something you could never calculate. The only sure thing is that something > nothing, meaning that whatever that amount is, it's more than the zero used while decelerating in gear.

Like I said - I've tuned a lot of cars. It's a pretty basic fuel injection fact that any manual-trans vehicle since the late 80s is set up the same way. If there was a such thing as a DIY scan tool for these trucks, I'd datalog and prove it.