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Old 11-12-2013, 07:31 PM   #1 (permalink)
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Drive by Wire Throttle tune = ~3 MPG gain & more

Background:
For those of you who are unfamiliar with Drive by wire throttles (DBW), they are basically 'electric' throttles. The computer in your machine (ECU) determines how much the throttle plate should be open based on several conditions including the accelerator pedal position. Almost all new cars have a drive by wire system now. DBW systems are often Not linear in function compared to traditional cabled throttles and DBW accelerator pedasl do Not directly control the throttle plate.

Issue:
My factory throttle mapping for my subaru was always a pain in my butt. After buying this car I started to sorely miss my cabled throttle in my old Honda. This Subaru Drive By Wire throttle (DBW) is so sensitive (presumably to attract buyers at testdrives) that I would accidentally go WOT at sometimes only 20% pedal travel. So an example: using scangauge, while accelerating, I would try to maintain 70% engine load at 2000rpm. but when transmission would shift all of a sudden my engine load (manifold pressure) would jump to 99%. This was because Subaru programmed for more throttle opening at lower pedal travels for lower engine speeds. This caused poor gas mileage in the city and I could accidentally use more throttle than I needed when hypermiling in traffic. Unwanted acceleration, a jerky drive and a fatigued foot were causing problems.

Solution:
I was desperate for a drive by wire tune for a more linear feel, at least for the first 1/4 of throttle travel. After much research and reading I learned to use an opensource Subaru tuning software to design my own Maps. I used a guide from a Subaru fan site and adjusted my DBW until I was satisfied.

Here are the drive by wire maps - before and after:

*I don't want to bore you with the technicals so skip this paragraph if you are not interested. Basically in the map above lower values 'could' mean less throttle plate opening, but note these values are checked against another table which determines how much requested torque means exactly how much throttle plate opening for every RPM. So >120 requested torque at 1500rpm could mean WOT while you will need at least 200 requested torques to open the throttle plate wide at 2500rpm. It's a 3D map.


Results:
WOW! Not only did my driving experience become silky smooth but engine Load stays very close after shifts. No more spikes in manifold pressure and unwanted accelerations. I really feel sorry for owners who are stuck with crappy factory tuned DBW throttles. Also when cruising it's very easy to feather the throttle to put the engine in its 'sweet spot'. So far for the past month I gained about ~3mpg in my city driving which is a massive improvement to my dismal 23mpg. The only downside is that the torque converter unlocks easier now since there is more pedal travel now. This has to do with TCU which I am not able to manipulate. Also engine load can fall to pretty low levels during acceleration if you're not careful which can induce pumping losses. But for experienced drivers armed with vacuum gauges, this is not an issue.

a graph to illustrate the change (red line is the new requested torque vs. stock black dots):

please note 'load' in this context is actually "absolute load"

Now at reasonable engine speeds <3000rpm and reasonable accelerator pedal positions <30%, the throttle response is almost linear. Above 30% accelerator pedal things start to pick up quickly. This was kept so to prevent pumping losses and throttle response problems.

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Last edited by ever_green; 11-12-2013 at 07:44 PM..
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Old 11-12-2013, 11:43 PM   #2 (permalink)
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I am curious how I could apply this to a Toyota vehicle
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Old 11-13-2013, 02:07 AM   #3 (permalink)
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Quote:
Originally Posted by TexasCotton View Post
I am curious how I could apply this to a Toyota vehicle
Agreed!

And also... subscribed! Very cool concept. I wonder if there is a way to trick the system into thinking it needs to lock up the converter when you want it to, instead of when it thinks it should. That might net you another couple of MPG.
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Old 11-13-2013, 03:46 AM   #4 (permalink)
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My toyota prius has a throttle with two potentiometers (for redundancy). It would be a fairly simple thing to splice in a microcontroller and two digital potentiometers to create any throttle position to signal map you like, probably something exponential where there is finer control at lower throttle and more rapid change towards full throttle (perhaps with limits to prevent any enrichment modes).

Weigh any such changes against the litigious nature of your locale, as well as actual dangers involved, which I will not go into here because they are largely counterproductive in the innovation space.

But in the case of the prius, it could tie into some feedback for the various efficiency operating modes, such as keeping it in EV mode or coasting mode (or opening it up more when the engine lights to reduce pumping losses). Certainly just having it coast when off the gas could be useful instead of regen.

Last edited by P-hack; 11-13-2013 at 03:53 AM..
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Old 11-13-2013, 06:30 AM   #5 (permalink)
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Ah, folks are doing something similar. Plug and play but expensive, and not quite the feature set I would hope for:
Pedal Commandertoyota Prius 1 8L Hybrid Throttle Controller Faster Acceleration | eBay
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Old 11-13-2013, 09:44 AM   #6 (permalink)
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Nice project.

Manufacturers are doing this more and more with "Eco" buttons that smooth/calm throttle inputs (among other things).

There was a similar mod done by Julian Edgar (Autospeed) and others for the 1st generation Honda Insight which was intended to smooth out throttle transitions in order to keep from accidentally kicking the engine out of lean burn mode. In that application, a capacitor was used to "buffer" the throttle signal: http://ecomodder.com/forum/showthrea...tor-25641.html
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Old 11-13-2013, 11:56 AM   #7 (permalink)
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Quote:
Originally Posted by jeff88 View Post
Agreed!

And also... subscribed! Very cool concept. I wonder if there is a way to trick the system into thinking it needs to lock up the converter when you want it to, instead of when it thinks it should. That might net you another couple of MPG.
not that I know of...I have heard of commercial softwares for scions like ECUTEK. but i'm not sure about toyotas. I have seen some people doing DBW to cable conversions though. There is growing support for software tunings on vehicles with growing role of computers on cars though. One other thing that can also be tuned is the variable timing and lift systems.

Quote:
Originally Posted by MetroMPG View Post
Nice project.

Manufacturers are doing this more and more with "Eco" buttons that smooth/calm throttle inputs (among other things).

There was a similar mod done by Julian Edgar (Autospeed) and others for the 1st generation Honda Insight which was intended to smooth out throttle transitions in order to keep from accidentally kicking the engine out of lean burn mode. In that application, a capacitor was used to "buffer" the throttle signal: http://ecomodder.com/forum/showthrea...tor-25641.html
thanks. Yes good thing about electronic systems in cars are that you do not need to have an engineering degree to mess with it.
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Old 11-14-2013, 10:33 AM   #8 (permalink)
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It's been done by our very own Orange4Boy: http://ecomodder.com/forum/showthrea...tch-10028.html

And for the Subie fans: Bobs Torque converter lockup mod (PhaseII 4eat/01 4eats) - Subaru Impreza GC8 & RS Forum & Community: RS25.com

This last one grabbed me in particular because virtually all of it translates word-for-word to work on my Forester. I can't tell if the 4EAT got bolted into any 09 Imprezas and of course the wiring might be different too, so YMMV. But you can see there are some possibilities.

For my own part, I would try to install a relay that depowered the TC lockup at the 3-2 downshift, so you couldn't accidentally leave the TC locked up at stoplights, for instance. It might become a tad troublesome to keep resetting the lockup, but how much cheaper is that against getting a new lockup clutch, especially when it permits you to skip gassing up for another day?

My Forester on its best day might break 24mpg. It's a great car when the snow flies, but man. It's thirsty.
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Old 11-14-2013, 11:08 AM   #9 (permalink)
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Quote:
Originally Posted by elhigh View Post
It's been done by our very own Orange4Boy: http://ecomodder.com/forum/showthrea...tch-10028.html

And for the Subie fans: Bobs Torque converter lockup mod (PhaseII 4eat/01 4eats) - Subaru Impreza GC8 & RS Forum & Community: RS25.com

This last one grabbed me in particular because virtually all of it translates word-for-word to work on my Forester. I can't tell if the 4EAT got bolted into any 09 Imprezas and of course the wiring might be different too, so YMMV. But you can see there are some possibilities.

For my own part, I would try to install a relay that depowered the TC lockup at the 3-2 downshift, so you couldn't accidentally leave the TC locked up at stoplights, for instance. It might become a tad troublesome to keep resetting the lockup, but how much cheaper is that against getting a new lockup clutch, especially when it permits you to skip gassing up for another day?

My Forester on its best day might break 24mpg. It's a great car when the snow flies, but man. It's thirsty.
ya those mods don't seem too easy to do (for me). my engine doesn't like lugging at all. high loads at low RPM for more than a second starts causing weird engine noises and poor mileage. i find its sweet spot to be around 2000rpm-2500rpm or 3000-3500rpm at moderate loads. since the torque converter is 2300rpm stall, it doesn't usually shoot up the rpm's too high. on the highway it will not unlock unless i go WOT. it's in the city that it unlocks easier now...but havent seen any negatives from the unlocking/locking itself yet. maybe an extra 0.5mpg to squeeze?
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Old 11-15-2013, 11:56 AM   #10 (permalink)
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Quote:
Originally Posted by P-hack View Post
Ah, folks are doing something similar. Plug and play but expensive, and not quite the feature set I would hope for:
Pedal Commandertoyota Prius 1 8L Hybrid Throttle Controller Faster Acceleration | eBay
unless you have installed this with a couple other drivers/posters and done a complete review.............I would not try for these reason.

Ebay seller out of country
reliablility
quality
install issues
not worth the risk of paying 300 bucks and then not working plus having negative impact on my vehicle..................

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