How to over-ride computer RPM while coasting?
 

My 2012 Toyota FJ Cruiser has a 6 speed manual. The vehicles computer adjusts the RPM's based upon the mph. For example, if I am going downhill (45 mph) and put the tranny in neutral and foot off the gas, the computer idles up to 1,500 rpm. The faster the mph, the faster the rpm. Typical manual trannys allow the vehicle to idle as normal at 6-700 rpm.

Has anybody on this forum been able to over-ride their car computer to adjust the idle as it should be?

Until I get around to proper wiring for my kill switch, I just use the key.

Does the vehicle have some kind of active rev matching?

Lots of cars do this. My Toyota Matrix did it as does my Metro. Until you're stopped, it won't idle down all the way. IMO its a pretty minor thing and I don't intend on trying to mod anything to 'fix' it. I'm not even sure you can. Even if you faked the signal, I think you'd create other issues with ABS and other stuff.

If I turned the car off, it would impact the power steering and possibly brakes...right?

Yes. I have heard it does this for two reasons....emissions and allow for easier shifting. I don't need it though.

I'm interested, as such a mod would roughly 1/2 the gas use while coasting.

Turning the car on and off is not always efficient, and has it's own issues.

Generally the brake system stores enough vacuum for three full presses. If you need anything close to that, your engine should be running.

Once you're moving, especially at driving (not parking lot) speeds, power steering doesn't add too much. Cars with electric steering have it come right back. I'd be concerned about whether an automatic transmission car would treat things like locking the column, but I can't really speak to that.

But shutting it off does override the computer's desire to keep the revs up. ;)

I doubt you'd ever pull off a swerve and recover without PS on an FJ Cruiser, I know my Wrangler won't.

The aerodynamics of these 4x4's is such that EOC isn't very practical anyway. If I do EOC occasionally, it's with the gearbox in gear and foot on the clutch ready to bump start at short notice.

EOnC is probably the preferred method, the only solution I can see to the problem is to spoof the ECU's speed input while in neutral. An ECU tuner might be able to help.

As far as the engine revving while coasting in neutral, i would start by measuring the fuel consumption when idling (stopped) and when coasting.

this!!!!
Get a scanguage and do this test in about 5 minutes.

it's easy to get fixated on something like this....had a tarsus that did the same thing.
But there are probably three other things you could do to get better mileage.
half of a quarter of a gallon OVER 1 hour is nothing.
maybe you can reduce the rpm in half, but it doesn't use twice as much gas to run 1500rpm (IN NEUTRAL). And honestly, how much time do you really spend coasting....:o;)

^That.

Also, based on my Wrangler and an expected 200,000mile life, I can actually buy a brand new Prius (inclusive of fuel and insurance) with the fuel savings. My Prius is actually 'free' as compared to using my Wrangler on a regular basis. I bought a used Prius so it actually 'makes' money. In fact I could even say I bought my Fiat brand new and the used Prius and got free fuel, with the fuel money from the Wrangler.

4x4's are awfully expensive to run. US figure will be a bit more SUV friendly I suspect.

that is a great thought. I have been considering a ScanGauge.

there is a function call "fuel per hour" or "consumption per hour" that shows an instant continuous reading.
So one day you can coast down a regular hill and stay in gear, and the next day you can coast the same hill in neutral.
The you can see the difference.
Remember, the gauge is giving you a gallon/hour reading so you have to divide by the guestimate of the number of minutes you actually coast.
God Luck!
(ps you can buy a scangauge from this site!!;):thumbup::D)

Please clarify. If coasting in neutral at 65 mph & 1500 rpm is 400 mpg, wouldn't 750 rpm in neutral at the same speed be 800 mpg, which is half the gas and double the mileage?

Same way that coasting at 65 at 1 rpm doesn't double the mileage from the 750 rpm. It's not a simple math equation. I would actually assume it is based on what is required to rim the engine. Engine load, gearing etc.
the issue, imho is consumption of fuel during the brief moments of coasting TO THEN justify a hack that might have unintended consequences.

The bigger issue is: is it worth it?
Ecomodding makes sense on a older car.
But in newer cars, when there is so much pressure on manufacturers to I crease corp mpg, do you REALLY think that they have left MPG's on the table?
Look at all the trouble dodge went to to achieve class leading mpg on a truck! The actually have an active dispersion to lower the body 1" to improve aero at speed.
I would bet that Toyota has a reason for the rpm NOT to drop.

It may simply be to throw enough BTUs down the exhaust pipe to keep the cat running. Look back here:

http://ecomodder.com/forum/showthrea...ing-20338.html

rpm ~ no significant effect on mileage
 

I'm interested in your tests of coasting at 1 rpm, and how they support your theory that coasting rpm makes no significant difference to mileage. Likewise, please post some evidence that 3000 rpm, for example, is no worse for mileage then 1500 rpm, and whether this applies to gas use when idling at a stop, as well as when coasting.

Fuel consumption is more dependent on engine load than engine speed, particularly when engine speeds are well below the normal torque curve. The question directly related to the OP and his/her situation: Is the additional fuel usage from the elevated idle enough to actually be concerned with? We don't know until it is measured.

read this.....again
it's easy to get fixated on something like this....had a tarsus that did the same thing.
But there are probably three other things you could do to get better mileage.half of a quarter of a gallon OVER 1 hour is nothing.
maybe you can reduce the rpm in half, but it doesn't use twice as much gas to run 1500rpm (IN NEUTRAL). And honestly, how much time do you really spend coasting....
__________________________________________________ ____
1.) buy a scangauge
2.) aba test your theory
3.) report back

you can discuss all the 'theories' you want until you are blue in the face.

everything in life is a bell curve. It's not worth dealing w the fringe stuff UNTIL you address the stuff in the middle.
SO....... how much time and distance is spent 'coasting'? (the fringe stuff) Which by the way has the LOWEST consumption of fuel on the whole trip probably only 10-15% of driving consumption.
FOCUS on the stuff that matters.

I'd like to see some evidence of 1 rpm vs 3000 rpm not making any difference to mileage when coasting in neutral, and the same when idling at a stop.

In my experience that is not true at all.

Plus if fuel use while coasting made no difference to mileage, then no one would use bump starting and engine off coasting.

it's easy to get fixated on something like this.... :rolleyes:

your question was already answered by another poster. you chose to ignore it. you keep repeating the same question.
AGAIN, in 2012 when the op's car was manufactured, Toyota (AND MOST OTHER BUILDERS) really were trying everything they could to get better mileage. So I would bet that the rpms being higher is for a pretty good reason. AND that changing it will have greater negative result than positive results.

Here chase this rabbit down a hole....learn to get out of your car VERY FAST so the air conditioning doesn't escape........and waste fuel.
Pay attention!!!!
FOCUS!

You spend a VERY little amount of time coasting. PERIOD.
Focus on what makes a difference.

and finally I didn't say "it didn't make any difference"....pay attention!
I said that there was not a simple "if this drops 50% than that drops 50%' relationship.

Which was answered....which you ignored. :rolleyes:

Yeah I can see that, the bold caps, exaggeration, ignoring facts etc. :rolleyes:

Meanwhile, no evidence. When you get that 1 rpm test completed let me know. :)

Personally I spend the majority of time coasting, instead of having my foot on the gas.

Maybe this will help....

I drive a Honda Insight, and for the past few months the HV battery is starting to get finicky, so I don't trickle charge it much.

When the HV battery voltage gets low, the ICE engine idle goes from a normal 1000 rpm, to about 1200 rpm or so.

The effect on gas consumption at idle?

FCU display stays maxed out at 150 mpg until I reach a coast down speed of 20 mph when idling at 1000 rpm.

FCU display stays maxed out at 150 mpg until 22 mpg when idling at 1200 rpm.

That's a difference of 10% in fuel consumption at idle.

The consumption at load is much higher than this, so the result of idling at 1200 rpm is pretty small in the grand scheme of things.

Jim.

So I have an update. I started using the DashCommand iPhone app so I get some data.
I have been looking at the gph while in neutral and while coasting downhill in 6th gear. The RPM's and gph remain the same weather in neutral or coasting downhill in 6th gear. Approx 1,100 rpm = .9gph (this is at 45 mph). So there is no savings in gph between coasting in gear or shifting to neutral.

My base idle at 600 rpm is .3 gph. So my ECU is nearly doubling my rpm and tripling my gph while I coast downhill at 45 mph (no foot on throttle). Tripling my gph is significant when it is not necessary. Older cars used to get better mpg than autos. Now the opposite is true. Part of the new inefficiency is our car's ECU not allowing our engines idle when we are coasting in neutral or gear.

What I did not know is if someone was able to link their laptop to a Toyota ECU and make a simple mod to reprogram this high idle. A friend of mine does some high end car tunes. He says Toyota's ECU's are really locked down for mods.

EPA doesn't test coasting in neutral, so that's not why autos sometimes do better on the EPA cycle.

Real world, manuals still beat autos.

Besides, you need to be at 2000rpm before gliding in gear to enter DFCO and use zero fuel. This isn't very useful in an FJ but works brilliantly in small cars. You can also key off with the car in gear, this keeps everything working but essentially means forced DFCO.

The math IS pretty simple, you just have to pause and consider what you're mathing.

One mile at 50mpg followed by one mile at 30mpg should average 40mpg, yes?

If so, then it follows that one mile at 5,000mpg followed by one mile at 30mpg would be 2,515mpg, and as we approach engine-off coasting, our average goes toward infinity. We know this is not the case though.

We're not interested in miles per gallon per mile, we're interested in gallons per mile. Burning 0.020 gallons over one mile (50mpg) followed by burning 0.033 gallons over one mile (30mpg) results in a total fuel consumption of 0.053 gallons over two miles, or 37.7mpg.

Doubling your MPG while coasting might look significant, but it's important to figure out exactly how much fuel you're actually saving. It might or might not be significant over a tank, depending on how much coasting you do.

This is why L/100km is a better metric than MPG. Going from 15 to 17mpg actually saves 50% more fuel than going from 60 to 90mpg; MPG obscures this.

~

Just as a thought exercise, if we assume 15mpg @ 60mph climbing one side of a hill for 30 minutes, and coasting down the other side (assume also at 60mph) for 30 minutes, just how much fuel can you save by reducing fuel consumption while coasting? Note that we're assuming 50% coasting in your normal driving - it's probably far less than this.

15mpg @ 60mph = 4 gallons / hour

If you coast at 0.40 gallons per hour on the other side at 3000rpm, you're going to use a total of 2.2 gallons to go 60 miles (again, with 50% coasting), resulting in 27.3mpg.

If you coast at 0.20 gallons per hour @ 700rpm, you're using 2.1 gallons to go 60 miles, resulting in 28.6mpg.

Approximately what percent time are you coasting, would you say?

So what you have in your example is a 4.8% improvement in MPG, and a 4.5% reduction in fuel consumption. Incremental changes add up, and an increment from a reduced idle seems worthwhile for those who pulse and glide on open roads, especially (from my experience) hilly ones.

On slow city streets I think I probably glide over half the time, and then there is time idling at stop signs and (sometimes engine off) traffic lights. So there is a lot of opportunity there to both save gas and improve mpg (or l/100-km) as well.

------ Later edit, Jan. 28

I have calculated my average idle time from a datalog. It is from a 13 minute trip at mostly 40-50 MPH (some 30-35), no stops, with 23 pulse/glide cycles, starting and ending at the same place.

I used power 26% of the time (average 9 seconds, range 2 to 29 seconds).

Idle RPM coast time was 56% (average 19.3 seconds, range 4 to 60 seconds). Low idle differed on the glides, 600 to 750 RPM, usually about 650 (Focuses have a mind of their own on this).

The remainder was the RPM decline with zero throttle (i.e. dash pot effect) which was 12% of the time (avg. 4.1 seconds, range 3 to 5 seconds). Notably, these drops are much faster than before tinkering when my "low" idle was 1500 to 1600 RPM (idle drop to get there, 7 to 8 seconds). The Focus is notorious for having a high idle (many complaints on other forums).

So, I am saving in two ways; lower idle and faster drop to idle, the latter being important to make the most out of P&G driving.

Lowering my idle as above has made a repeatable difference of about 38 vs 41 MPG on this same route, measured on an UltraGauge, which is nearly an 8% gain.

You need to reflash the ECU for this. Nobody has bothered to develop such a thing because there is no money in it. There is a fair bit of economy left on the table but at the expense of tailpipe emissions. Changing the shifting program is one of the most effective ways to do it without changing the tailpipe output.

-Michael

No.
One mile at 50mpg uses 1/50 gallon, one mile at 30mpg uses 1/30 gallon,
for a total of two miles at 1/50 + 1/30 = 8/150 gallon,
for an average of 2/(8/150) = 37.5mpg

Got the email for this thread today, and it caught my eye so I've read through it. I might have another answer for you guys as to why manual cars in particular do this, and I'm pretty sure it has little to do with the ECU.

First, some details on my own car; it's a 2009 Mazdaspeed 3 with factory drive by wire and electronic throttle body.

Now, for some anecdotal information:
A few years ago, I was redoing the PCV setup on my car to help with oil going all over the place in the intake and whatnot, and I completely bypassed (capped) the line going into the intake manifold (post throttle body). It ran fine except under one condition: Holding the clutch in after hitting high RPMs and letting the car coast.

With no air bypassing the throttle body (via PCV), RPMs would drop sub-idle and usually stall. Sometimes it would hunt for idle RPM a few times, but normally it would stall out. I fixed this issue by installing a hose to the intake manifold with a low spring check valve that goes to the intake, post MAF (so it doesn't pull in unmetered air).

My thought is that there's still some coupling going on which is causing the engine RPMs to run higher than idle (similar to how a manual car in neutral on jackstands will have the drive wheels turn slowly).

I vaguely recall seeing the throttle body reading the same as idle or below idle settings when I was troubleshooting this issue myself, but I've asked a friend to pull some logged data for me to confirm since my car is down. I should have the data within a couple of hours of the time of this post.

Stay tuned!

OK so it looks like my particular vehicle isn't trying to increase RPM on decel (rev matching). It takes about 5 seconds to go from 3k rpm to 6700 at right around 25% pedal, which is roughly the same throttle on his tune (we can change this and mine isn't linear like his is).

It takes 4 seconds for the engine to spin back down to idle, in which it hunts for idle a little bit and modulates the throttle position to do so (no change in pedal). Overall, it's trying to keep the throttle right around what it normally is at idle.

Sorry this theory doesn't pan out on my end, but it might be worth looking into on yours with some kind of monitoring device; I'd check idle valve duty cycle if there is one, as well as throttle position and compare between (hot) idle and when you encounter the issue. It's worth noting that it might be that your clutch isn't floating on the input shaft properly for whatever reason, and might still have a bit of friction against either the pressure plate or flywheel and thus, run higher while coasting.

Just a thought.

And it may affect the lubrication of your automatic transmission. Check your model of car to see if it is OK for 'dinghy-towing' or 'four-wheel towing' as if behind a motorhome. If it is not OK for dinghy-towing it may mean that with the engine off, lubricating fluid does not cycle through the moving parts of your transmission--even though you are in neutral. I used to engine-off-coast (EOC) in my automatic transmission Matrix till I was advised of checking whether the model was approved for dinghy-towing and, sure enough, it is not approved! I don't EOC anymore, fearing damage to my car. I just coast, engine on, in neutral.

My 87 Dodge Daytona does this and it drove me crazy. Discovered different conditions vary coasting idle from 800-1,200 rpm. But, the biggest is when the front windshield defroster is on with the fan switch engaged then it's 1,500 rpm until almost stopped when it drops to 800 rpm. The easy fix is to press the bi level button and move the fan switch one notch higher. Some drivers run a independent power wire to bypass the computer and/or cut the sensor wire to the computer.
The Daytona has a transplanted 2.5 turbo 5 speed with some mild performance mods and fat 225 tires. Unfortunately it's ganged fuel injected that can only be fixed with a ECU change & that's above my pay grade so it only gets 17 ½ in town, 24 mix if lucky. However, highways a different story.
Aero's Work!
I flared the front nose plastic fascia (easy mod that looks good) to cover the tires and installed a black chloroplast belly pan (almost invisible) from the nose to the engine, about $20. The belly pan slips into & overlaps the front bumper cover and attaches with heavy duty Velcro for fast easy removal. This made a massive improvement not only in highway mileage but wind noise reduction. Also installed is a modified spoiler off a little Chevy S10 pickup using R clips for fast removal. I can remove both pan and spoiler in under 1 minute. Although the spoiler doesn't make any mpg difference it does help handling but also scrapes over every speed bump. This old car won't take a Scanguage without major wiring hacks but came with a primitive version stock that matches the odometer readings. Puget Sound highways are all up and down, rarely flat. In 80 degree weather I consistently get between 36-38 mpg at 58-60mph. Retarding the timing a few degrees, flat ground, good gas, a 5 mph tail wind, 55-58 mph, careful right foot and she does 43 mpg. Today I drove in a 18 wheeler's slip stream and did 59 mpg. In a few months I plan to flair the rear fender skirt and install a belly pan to cover the massive parachute bumper hole. Hoping for another 1 mpg highway.

Most vehicles kick on the AC compressor for defrost; not entirely sure why other than possibly engine load (more heat faster) and temp control of the defrosting air.

I have a scanguage on the ranger, and coasting at 60kph at idle (750rpm) I will get 65MPG or more, while at 2000 RPM I'm getting closer to 30.
At 100 kph I may get 144MPG at idle and closer to 50 at 2000 RPM. I'll have to record actual mileafe next time I do it - but it is VERY substantial.

I moved the scanguage to the Taurus to see what happens there last summer, and coasting in gear or out makes no difference in mileage because the revs match the speed when in neutral and their is no closed throttle fuel cut - so "pulse and glide" doesn't buy me anything on the Taurus.

With the Ranger (4 liter 5 speed 2.55 ratio and 235/70-16 tires) on my Wedneday trip to the local airport just coasting on the hills changes my fuel consumption from 20 MPG without to 24-27 with coasting - on a 15Km trip, about1/3 in urban traffic - rolling land in the Grand River Valley of Ontario