Downshifting Etiquette

[toyotaspeed90]

I'm not suggesting the fan clutch is on/off. In short the purpose of the fan is to move air when natural flow is reduced (ie, driving at speed). Otherwise it IS a hindrance to the cooling system (drag on the engine and resistance for that natural airflow).

Fuel isn't cut completely at deceleration, otherwise the engine would shut down. It does, however, have a deceleration function/table that reduces fuel injector duration. Engine rpm decreases due to the throttle body shutting and effectively giving the engine little to no air.

Fuel and spark continue to be delivered- only exception to this is the rev limiter, which depending on how the sytem is set up, can be a fuel and/or spark cut.

 

[Bad Luck]

If all else is equal, more flow always makes better cooling. Always. It’s given by the equation Q=mcdT. m is mass flowrate, Q is heat. (Again, all else equal here). The thermostat will regulate flow rate rate of the coolant along with the water pump. You always have a very slight bypass of the thermostat with that jitter valve, then once it cracks you get a lot less dP across the valve (more flow if the pump is running). So the rpm on that water pump matters to coolant flow rate (along with thermostat).

Do you have some fan clutch data? Everything I’ve read says even fully disengaged you get 20/30% of shaft speed, which tells me fan rpm is never truly capped.

You won’t have any brakes to stop you in the first place if you ride them down an entire grade! That’s the entire point lol. And my point still stands, it’s even safer to be in lower gears in low traction scenarios. Why do you think your transfer case further gears you down upon engaging 4Lo lol.

Try removing your thermostat and driving around for awhile to tell me how well your higher flow rate works for you.

You completely missed my point regarding low traction scenarios. I also know how to brake during long grades and don't engage them the whole time. Let's say you're using your "engine braking" while going down an icy grade and your engine braking exceeds the traction of the road. All of a sudden you're doing 40 mph on an icy road with the rear of the vehicle sliding (possibly all 4 sliding) what do you do? It's a curve so you better think quickly! Too late you forgot to put it back in drive and instead panicked and hit the brakes further worsening your slide, hit a guardrail, went tires to Jesus a couple times, and now you're having a really bad day. Am I exaggerating? Yes. Is it still possible? Also, yes.

While we're at it, there is no such thing as warped rotors. What is misconstrued as warped rotors is really an uneven application of brake material caused by heating the rotors/pads up too much AND not letting the cool properly before parking the vehicle or stopping for an amount of time. Don't believe me? Take a trip to your local google and research it yourself. Enjoy your weekend and I'll be back on Monday :llama:

 

[jmansfield]

I'm not suggesting the fan clutch is on/off. In short the purpose of the fan is to move air when natural flow is reduced (ie, driving at speed). Otherwise it IS a hindrance to the cooling system (drag on the engine and resistance for that natural airflow).

Fuel isn't cut completely at deceleration, otherwise the engine would shut down. It does, however, have a deceleration function/table that reduces fuel injector duration. Engine rpm decreases due to the throttle body shutting and effectively giving the engine little to no air.

Fuel and spark continue to be delivered- only exception to this is the rev limiter, which depending on how the sytem is set up, can be a fuel and/or spark cut.

Do you know that for a fact on our 4Runners?

Most modern cars do cut fuel for efficiency and emissions (though I don’t know about our 4Runners specifically):

automotive engineering - While going downhill, does my car consume less fuel when in neutral or in gear? - Engineering Stack Exchange

Engine won’t stall if it is being back driven by the movement of the car (i.e. through the trans and tc). If you back drive the engine via wheels turning and the transmission there is no need for fuel.

 

[Sieuphan]

I drive a lot of sports cars and am used to downshifting.. that being said I have an automatic 4runner and will use it to downshift, probably higher rpms than I should, but it works well.

I live in an area with lots of hills and my gtr required a brake job after 7 months at the cost of $4k ��. 4Runner needed a brake job after 3 months..

 

[toyotaspeed90]

No. Toyota ECUs are locked down. While you can make some internal component changes (like reclocking the crystal) you can't modify them like with an Epsom based system. It's also why if you boost the motor you have to use a 7th injector and external system to control it or go full standalone.

However I can deduce it doesn't cut fuel. This is based on a typical 90s Toyota ECU system. Then only "upgrade" is that i doesnt utilize an additional injector for the cold start sequence (something they used on popular engines like the 4a, 5s, etc) - but in short it's a pretty rudimentary EFI system. I haven't torn the injector wiring on one but I'm willing to bet it's a batch system (not all at once - which they have used as well, but they 'graduated' from that in the early 90s). Toyota uses a 4 wire TPS on these which is actually unique (most manufacturers use a 3 wire system - ground, 5v ref, and a potentiometer signal - assuming the lowest signal is the TB being shut... Toyota has a 4th wire that registers the TB shut and tells the ecu ro, possibly, be in idle mode there's more ro the idle circuit, but still). The ignition system I'm guessing is a wasted spark as 2 cylinders share 1 coil each.

In short - this system is pretty simple. Newer advancements like direct injection, sequential injection, COP (and the control those give) just weren't available or used on these rigs.

I'm done, we're way off topic here.

My $0.02.

 

[St Runner]

I downshift all the time. Its second nature in my 5speed but I also do it on the steeper switchbacks in my auto. As a rule of thumb the steeper and slower you are going, the more you should use engine braking. I personally have never warped a rotor but in tourist season I smell burning brakes at least once a week. I run engine load on my ultraguage. Under engine braking once the rpms get over 1700 the ecu goes into open loop and the engine load drops from 14%(idle) to 7%. It does it in both the auto and the 5 speed ecu

 

[DAW89446]

I practice downshifting whether in my manual transmission Tacoma TRD or automatic transmission 4Runner or Subaru Outback. And many other vehicles. I do so to stay off the brakes on grades.

I’ve done so for so long I never give thought to RPM, it just comes natural and my engine speeds are not excessive. I use the engine/transmission to brake on pavement, dirt, in 2WD, 4WD and low range if necessary.

Never had engine problems, transmission problems. Brakes on all my vehicles have lasted the life of the vehicle, most in my possession five to twenty years, up to 300,000 miles.

 

[PatrickStapler]

Now I’m worried about my trans!

I didn’t realize this was an issue. My truck has 315K on it. I tow this short distances. Should I be worried?

YouTube

I upshift it at 6500...

 

[absalom]

Living in Colorado, downshifting on steep grades is (or seems to be) mandatory.

Some of the posters in here are way overthinking it. Downshift to whatever gear you need, generally try and keep your RPMs below 3,500. I mean, what's the alternative; riding my brakes all the way down i-70?? That's crazy talk ...

 

[rightyouareken]

I live on a plateau and there are two ~mile long very steep hills that drop me down towards town. One has a speed limit of 45 MPH, and I can either ride the brakes all the way down or click off O/D to keep speeds around 45-50. The other is steeper, and has a limit of 35MPH. I general drop down into second on this hill.

Both hills have a stop light immediately at the bottom...so there is no room for the brakes to cool before needing to fully stop. If cars ride the brakes all the way down, then sit at the light at the bottom, it's a great way to warp the rotors and/or leave pad deposits which cause brake pulsing.

I've also been on some wheeling trips where engine braking is mandatory due to 5+ mile constant grades dropping 4-6k feet. That will cook the brakes in a hurry.

Like you, I don't let my engine braking RPMs get above 3k RPM.

I try not to engine brake unless I really need to though. Brakes are certainly cheaper than a transmission.

 

[phattyduck]

I live on a plateau and there are two ~mile long very steep hills that drop me down towards town. One has a speed limit of 45 MPH, and I can either ride the brakes all the way down or click off O/D to keep speeds around 45-50. The other is steeper, and has a limit of 35MPH. I general drop down into second on this hill.

Both hills have a stop light immediately at the bottom...so there is no room for the brakes to cool before needing to fully stop. If cars ride the brakes all the way down, then sit at the light at the bottom, it's a great way to warp the rotors and/or leave pad deposits which cause brake pulsing.

I've also been on some wheeling trips where engine braking is mandatory due to 5+ mile constant grades dropping 4-6k feet. That will cook the brakes in a hurry.

Like you, I don't let my engine braking RPMs get above 3k RPM.

I try not to engine brake unless I really need to though. Brakes are certainly cheaper than a transmission.

Those are the perfect situations to use engine braking, even in an automatic. Saving many brake applications (keeping them cool) and controlling speed for long(ish) periods of time.

In the original post, it sounds like he was suggesting to downshift the automatic around town for normal day-to-day driving, which isn't reasonable or normal...

-Charlie

 

[phattyduck]

I'm not suggesting the fan clutch is on/off. In short the purpose of the fan is to move air when natural flow is reduced (ie, driving at speed). Otherwise it IS a hindrance to the cooling system (drag on the engine and resistance for that natural airflow).

Fuel isn't cut completely at deceleration, otherwise the engine would shut down. It does, however, have a deceleration function/table that reduces fuel injector duration. Engine rpm decreases due to the throttle body shutting and effectively giving the engine little to no air.

Fuel and spark continue to be delivered- only exception to this is the rev limiter, which depending on how the sytem is set up, can be a fuel and/or spark cut.

Fuel is absolutely fully cut above a certain RPM. Generally coasting above somewhere between 1200 and 1600 rpm, depending on conditions (this has been the case on basically all EFI cars since the beginning). As engine RPM returns towards idle, fuel is re-introduced to 'catch' engine RPMs to keep it from stalling.

-Charlie

 

[phattyduck]

It's safer in low traction conditions to use your brakes. The reason behind this is your brakes have ABS/Stability controls and your engine does not.

Engine braking will never lock up your tires. Most 3rd gens do not have any sort of stability control. The 3-channel ABS that most have is not all that effective, and won't help as much as more modern systems.

I'd rather go down a snowy/icy hill in 4WD in low gear than try to control my speed with brakes alone... It has kept me safe in all my AWD and 4WD vehicles in the past.

-Charlie

 

[jmansfield]

Living in Colorado, downshifting on steep grades is (or seems to be) mandatory.

Some of the posters in here are way overthinking it. Downshift to whatever gear you need, generally try and keep your RPMs below 3,500. I mean, what's the alternative; riding my brakes all the way down i-70?? That's crazy talk ...

Exactly. There is literally no other option in some mountain scenarios.

I was looking around on Google Maps, here are a few of the steeper grades I've been down in California:

Whitney Portal (leads to Mt Whitney trail head): 10.8% for 1.4 miles, 9.7% for 4.7 miles, overall 7.6% (4,400ft descent) for 10.9 miles
Kennedy Meadows/Sherman Pass Road: 10.4% for 1.1 miles, 7.5% for 8.6 miles overall
190 from Death Valley to Panamint Valley: 9.1% for 2.5 miles, 7.5% for 8 miles overall
Horshoe Meadows Road: 9.5% for 1.2 miles, 7.5% (4,000ft descent) for 10.2 miles overall

These are all curvy, one lane roads, with steep mountain on one side and sheer drop-off on the other (except the 190 between Death Valley and Panamint). If you go off the road on any of these, you're falling a few hundred feet to your death (again except the 190). You absolutely need to engine brake in these scenarios. Fortunately, your engine and tranny will be just fine.

 

[Bad Luck]

Engine braking will never lock up your tires. Most 3rd gens do not have any sort of stability control. The 3-channel ABS that most have is not all that effective, and won't help as much as more modern systems.

I'd rather go down a snowy/icy hill in 4WD in low gear than try to control my speed with brakes alone... It has kept me safe in all my AWD and 4WD vehicles in the past.

-Charlie

Engine braking has caused my rear end to slide sideways while descending a muddy slope. I had to put in neutral and apply my brakes to regain control.

 

[rightyouareken]

Engine braking has caused my rear end to slide sideways while descending a muddy slope. I had to put in neutral and apply my brakes to regain control.

Engine braking can absolutely upset the balance of a car if it's done abruptly, at the wrong time (like in a turn), or on a slippery surface.

People who drive on the track know it all too well...trying to downshift in a turn and not matching revs properly can absolutely cause a loss of traction and a spin...it's why drivers "heal & toe" downshift to minimize the shock of the increased engine braking associated with a downshift.

 

[toyotaspeed90]

Fuel is absolutely fully cut above a certain RPM. Generally coasting above somewhere between 1200 and 1600 rpm, depending on conditions (this has been the case on basically all EFI cars since the beginning). As engine RPM returns towards idle, fuel is re-introduced to 'catch' engine RPMs to keep it from stalling.

-Charlie

I would be curious to look at real time or data logged information of the injector pulsewidths.

If this is truly the case then I would assume its above 1200 rpms, as that's usually the cutoff for the idle circuit (which won't go into idle mode and for dizzy-based systems you cannot set base timing without idle mode working)

First I have a hard time believing fuel is completely cut on a batch based ECU system - sequential makes sense as theres control of the fuel of a given cylinder, but the batch system would be cutting fuel to multiple cylinders at the same time.

Admittedly my experience has mostly been with Megasquirt- in data logging, building tables/maps, and real time watching of actual injector pulsewidths.

Agreed that fuel is reduced significantly- theres no acceleration increase from the TPS, however shutting the TB would change the airflow/map reading - and admittedly the volumetric efficiency would be quite low... but when I've built and seen maps, it isnt set to zero. You then add in the deceleration factors and, again, theres still fuel VEs.

 

[phattyduck]

I would be curious to look at real time or data logged information of the injector pulsewidths.

If this is truly the case then I would assume its above 1200 rpms, as that's usually the cutoff for the idle circuit (which won't go into idle mode and for dizzy-based systems you cannot set base timing without idle mode working)

First I have a hard time believing fuel is completely cut on a batch based ECU system - sequential makes sense as theres control of the fuel of a given cylinder, but the batch system would be cutting fuel to multiple cylinders at the same time.

Admittedly my experience has mostly been with Megasquirt- in data logging, building tables/maps, and real time watching of actual injector pulsewidths.

Agreed that fuel is reduced significantly- theres no acceleration increase from the TPS, however shutting the TB would change the airflow/map reading - and admittedly the volumetric efficiency would be quite low... but when I've built and seen maps, it isnt set to zero. You then add in the deceleration factors and, again, theres still fuel VEs.

You don't really need to log. You can do it with a Scangauge or equivalent. Batch vs. sequential injection doesn't matter for this discussion. The Megasquirt is either missing deceleration fuel cut as a feature or you don't have it turned on.

This article gets it mostly correct: Coasting in Neutral or Gear to Save Gas - Coasting and Fuel Economy

Other links (various vehicles, etc. - just spend some time on google):
https://www.z28.com/threads/injector-pulse-width.178639/
Does EEC-V PCM shut off injectors when COASTING? | The Ranger Station
Fuel Injector shut-off while Coasting - Fuelly Forums

The action is very obvious in a manual transmission car - you just coast in gear all the way to idle. You'll feel the fuel injectors turn back on before the engine gets all the way back to idle (the engine braking force suddenly reduces). It is less obvious with the 4Runner auto, since the ECU releases the torque converter lock while coasting, so you can't feel subtle changes in engine power output as easily.

-Charlie