Downshifting

[revetec]

Actually...post the RPM that the injectors start to operate. It would be good to compare vehicles. My Holden Caprice has a GenIII V8 and uses a Delco ECM.

[CapnBoost]

I can't look at logs unfortunately but my injectors kick in between 1000-1200 rpm at ~1% over normal idle duty cycle. I moved my idle from 700rpm to 1000rpm and nothing changed.

[revetec]

My Caprice injectors cut back in around 1,200rpm.

[Cernicalo1]

Guys,
I apologize for reviving this old thread, but I am trying to solve an issue that has prompted me to ask an additional question.
When downshifting a modern fuel injected vehicle with standard type intake and exhaust valve operation, how does the incoming air enter the manifold? Does the negative pressure created by the engine force the throttle body open, so the air can get in as it does while accelerating, and if so, does the throttle body position sensor activation causes a release of fuel by the injectors?

Pease help me clarify my confusion.
Thanks,
Infante

[csl177]

Welcome, Infante. To answer your questions: through the intake (where else?), no, and no. Hope that's clarifying enough.

Some basic books on ICEs should help.

[Lagonda]

so the injectors stop "throwing" petrol inside the cilinders completly? if one had a trip only on an incline that would keep the car moving, 5th/6th gear in, it would have 0 consuption?

Also when we downshift to help the breaking, without using heal and toe, does it also have 0 consuption? same principle aplies? even on very brutal downshifts?

Yes.

It really is very simple. As long as you're not pressing the gas you are using zero fuel. The gear you're in or the rpm are completely irrelevant. Even if you're running 10000 rpm you won't use any fuel if you don't step on the gas.

Also, coasting with your gearbox in neutral is essentially the same as standing still and idleing. Which obviously uses fuel to keep your engine from stalling.

EDIT: whoops I just realised that this is a pretty old thread!

[ruim20]

Yes.

It really is very simple. As long as you're not pressing the gas you are using zero fuel. The gear you're in or the rpm are completely irrelevant. Even if you're running 10000 rpm you won't use any fuel if you don't step on the gas.

Also, coasting with your gearbox in neutral is essentially the same as standing still and idleing. Which obviously uses fuel to keep your engine from stalling.

EDIT: whoops I just realised that this is a pretty old thread!

Old thread, but importante non the less, thanks for that

[culver]

Old thread but depending on the ECU, not pressing the gas may still used fuel. On a long down hill the engine is very likely to keep some fuel flowing if nothing else to keep the engine up to temperature.

[cmcpokey]

wouldn't it always give idle levels of fuel with the throttle lifted?

[pimento]

Nope cmc, the wheels will drive the engine so the ECU shuts down the injectors as a fuel saving measure. Not sure what the effect on a carburetted engine is.

[cmcpokey]

interesting... i had no idea. although i would expect that isnt the case on a carb.

[culver]

It's wouldn't give idle levels but not all engines will cut the fuel flow to zero.

[Gotmilk]

This actually gives me a question since I'm new to driving.

The instructor that taught my sister told her to not change gears when she's slowing down to take a turn/corner. But that's kinda illogical right? I mean my dad does it.

I do it. But when I do the car "pulls" and makes a strange sound.

[pimento]

Depends on how much you're slowing by, but before the corner is when to downshift if required.

[IBrake4Rainbows]

Pimento has it in one - you don't want to have to change gears mid corner - that means you didn't enter the corner correctly.

Changing down while slowing down for a corner is a wise decision provided the corner is slow enough. These days driving instructors will teach you not to change down gears when coming to a stop at traffic lights, this is also crap - change to an appropriate gear or engage the clutch. It's all to do with making sure your brakelights are showing - something changing down gears supposedly doesn't do...