Shifting from neutral to reverse while driving..

good ideal

 

I suppose it depends on your definition of stall out..

Let me put it this way...if I take the truck to some speed and pull my foot of the gas and slip it into neutral. Then turn off the ignition...do you think I'll feel anything different? By your explanation I shouldn't: the gas had been turned off when I popped it into neutral and, so, the engine should have 'stopped' by then due to fuel starvation.

I haven't done this, but my money says I'll feel the truck lurch slightly and decelerate faster, steering will suddenly become massively difficult and brakes only have one or two more pumps before THEY become so much more difficult. Why? because gas (as well as the ignition) is TRULY turned off now and the engine isn't powering accessories! The torque converter can't turn the engine over.

Turn it back on and I expect it will decel at the usual rate as ignition and gas is turned back on allowing the engine to run and everything operate normally.

I just don't see the ECU turning gas 'off', it reduces it...doubtless to no less than a normal idle, maybe a tad more.

 

this is correct and AFAIK std for all EFI vehicles. If the vehicle is moving (and there may be a speed threshold), in gear, and you are off the throttle (idle), the fuel injectors shut down because there is no need to inject fuel. At this point the tires are driving the engine back thru the drivetrain. So you are not saving gas in neutral down hills- as others have pointed out. And it is certainly not safer to be in neutral than in gear.

 

I think you voided your warranty on your auto if Toyota checks this forum...

 

I think it's also why you're not supposed to tow auto's in neutral without disconnecting the drive wheels. It's OK for a little bit, but no lubrication spells disaster for the internals!

 

That is wrong and you'll see why...no fuel in the engine means the engine can't operate...no engine and the accessories don't operate...no accessories means no power steering and no vacuum for the brake booster.

The engine can't be driven backwards through the torque converter.

Try my experiment a couple posts back sometime if you doubt me...

 

Just for information: This isn't the case with the manuals. On mine, if I coast in gear down a particular downhill stretch of the freeway, my mpg reading on my Aeroforce gauge shows about 69-75 mpg, depending on how fast I'm going. When I take it out of gear and let it coast in neutral, it jumps to about 100-105mpg.

Also when I'm decelerating in gear, the gauge will jump up to a particular mpg reading (e.g. 45mpg) when I first let off the accelerator and slowly come down as my speed slows, indicating that gas is flowing but the vehicle is not covering as much mileage with that particular gas flow.

If the engine is cutting off gas flow for the auto, I don't know why it wouldn't do so as well for the manual: same engine, same ecu.

 

Interesting...
I have witnessed auto trans vehicles push started - how do you explain this, given your statement?

 

Injector Duty Cycle = 0. This is the case when you take your foot off the gas pedal and the truck is moving forward in gear (at least faster than the speed it would move in 1st gear with no throttle input (manual) ).

I got a good chuckle out of several posts in this thread.

=D

 

The ECU shuts down injectors when throttle input is zero and certain other conditions are met. Cars have been doing this since not long after computerized controls were implemented.

Since the input shaft is turning when the ECU shuts down the injectors, there is pressure in the transmission control hydraulics, which means the transmission continues to function, which means the front pump keeps rotating, which maintains pressure, allowing it to transmit power from the driveshaft to the engine, driving the engine.

Oh, and as long as the driveshaft is turning the engine, even with the injectors turned off, the power driven accessories and vacuum accessories continue to function as normal. The presence or absence of gasoline in the cylinders of a driven engine does not affect the function of the alternator, power steering pump, or brake vacuum booster.

 

Easier to do in transmissions with both a front pump (driven by the input shaft) and a rear pump (driven by the output shaft). Older Chrysler torqueflites (pre-1965 or 66) had a rear pump too, so they could be push-started or towed with the rear wheels on the ground for significant distances without damaging the transmission. The rear pump supplied enough pressure and flow to lubricate the internals of the transmission and engage its hydraulic controls.

 

Then go out and turn the ignition off while coasting down the road in neutral...everything shuts down...no power steering...no power brakes...no engine braking. I know, I did it on the way home from work.

It just doesn't happen the way you think. Remember: the OP's situation is putting the tranny in neutral to coast down. Obviously there's little reason to keep on pumping gas when in D and using engine braking (what little there is with an auto). But it's not fair to say the injectors are 'shut down', they just need a little throttle and the gas flows again. Just like the carburetors of old, but a lot more efficiently.

 

Lots of people THINK it because they thought it was auto but it was actually manual, or any of a number of other possible reasons. Do you know the make/year/model of the vehicle you saw?

 

Exactly my point! so if you're in neutral and the injectors are 'shut down'...what would you expect to happen?

 

Me thinks buddywh1 has gotten himself confused. He was first saying that the injectors do not shut down in gear otherwise you'll loose you steering. Now he's saying if you shut it down in neutral toll loose your steering. The key difference here is gear/neutral. In gear while moving the wheels are turning the engine and all it's attached parts. No need for fuel. In neutral you have disconnected the wheels in essence, and therefore in order to keep the engine spinning you have to inject fuel. Big difference between the two.

 

Methinks everyone was confused...the OP's original question pertained to putting it in neutral and I just assumed everyone was talking about that scenario...

 

Agreed. So moral of the story is OP should just leave it in gear. Which will save some gas and give him power on demand in case of an emergency situation.

 

There was a time when you could "bump start" an auto in about any car out there that had one. It required that the vehicle attain at least 30 mph & you could move the gear shifter (usually on the steering coullum back then) from neutral to drive/drive2 & if all went as planned the spinning converter would build enough pressure to engage enough to spin the motor ('66 Dodge Darts were great for this ) seen it /done it !

 

I personally push (or roll) started my '64 Plymouth with an A-904-LA Torqueflite transmission on several occasions.

 

As soon as you put the transmission in Neutral, the computer will restart the injectors.

It can either use a metered or table-lookup injector pulse width that is appropriate for that engine RPM, throttle position, and other factors, or it can shut the injector completely off. Anything in-between produces an over-lean condition and will result in engine damage. It can't reduce the gas, it either delivers the correct amount or none at all.

Post #4 of this thread started the discussion about coasting in gear and injector shutoff. For the rest of the thread, the discussion of injector shut-down was clearly regarding how the vehicle operates while in a drive gear and under lift-throttle deceleration.

With the transmission in a forward drive gear, the motion and momentum of the vehicle will drive the engine through the transmission with or without injectors firing. The ECM shuts down the injectors under certain conditions of lift-throttle deceleration. This does not result in the loss of any power or vacuum accessories.

If the transmission is in neutral and you shut the engine off, the engine stops (along with power and vacuum supply) because there is neither combustion nor momentum powering the engine's rotation.