Exhaust sound & injectors w/ no throttle?

[Zenja]

I know that probably most cars (at least fuel injected ones) with a manual transmission shut off injectors when no throttle is given. I always wondered what then creates the exhaust sound if there is no combustion going on? Is it just air moving or engine parts moving?

Also, do pretty much all fuel injected cars shut off injectors when no throttle is given? If not, then is there any characteristic that distinguishes ones that do from ones that don't?

 

[Auladan]

Are you talking about idle (when the car isn't moving, but the motor is running)?

If so, the injectors never completely shut off. Without combustion, a motor can't run. So when the car is idling, your injectors are still feeding the motor with small ammounts of gas. The RPM guage should show you what rotations per minute your pistons are operating at, both at idle and when moving.

So, when the motor is running there is always combustions, thus exhaust. Even when idling.

Does that answer your question?

 

[psychlow]

Are you talking about idle (when the car isn't moving, but the motor is running)?

I think he's referring to deceleration while in gear. Not sure though.

 

[Quasimondo]

It's still getting minimal gas even when decelerating. Decelrating with the engine on and decelrating with the engine off will have different sounds. The difference is more pronounced when you have an aftermarket exhaust and can hear your exhaust more pronounced.

 

[Zenja]

Sorry, I forgot to mention that this is in gear.

My logger shows that injector pulse width is 0ms under these conditions. Doesn't this mean that no gas is being used?

 

[c5chris]

Exhaust note during deceleration can be even as loud as that during WOT since your engine is revving more freely when it is out of gear. This is also known as resonance.

 

[Fakie]

I agree. I have HKS cat back with test pipe...and when I let off the gas in gear it gets a lot louder than if I give a little gas. as far as 0ms injector pulse goes...I dont know the answer to that one...I would assume there is still some fuel being used...otherwise you would just be turning it over with no fuel.