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Old 05-20-2015, 01:31 AM   #1 (permalink)
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Push button start hypermiling

Hey everyone,

I'm trying to pick up a Subaru BRZ as my next car since it's a pretty balanced vehicle that has pretty good mpg potential (1st goal is 50mpg freeway which I think is doable with minor mods).

The only thing is that on craigslist I'm only seeing Limited models (do not want an FR-S, don't like the interior). Limited = heated seats, auto climate control, keyless entry, push button start. I'm never going to use the first 2 features but the slightly nicer interior is worth the money IMO.

What I'm worried about though is push-button start. I've tried a BRZ with this as well as an Altima rental, and while I think I could get used to it, I realized starting and stopping during traffic is a bit cumbersome because there's a delay, and I don't know if the car would allow me to shut off the engine for long coasts, or start the engine while coasting.

Has anyone had experience with a push button start car? I guess I could install a kill switch but that seems kind of stupid.

EDIT: it seems like the engine can be shut off while the car is rolling, but you have to hold the button for 3 sec :/ When you're stopped it forces you to shut all power off. Who the hell designed this...


Last edited by serialk11r; 05-20-2015 at 02:27 AM..
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Old 05-20-2015, 07:40 AM   #2 (permalink)
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I think you'll have to wire in a separate ignition and starter switch. The engine will only crank with your foot on the brake, which could be a problem if you've misjudged the traffic ahead and need the engine to crank immediately without loosing any more momentum.

Also yes, you have to go: Ignition Off> All Off> Restart. You can't simply go Ignition off> Ignition On> Bump Start. In fact you might not be able to do bump starts at all, because you might not be able to switch the ignition back on without also spinning up the starter motor.

The keyless system is likely a separate module and could probably be removed if you have the right software to sort out the CAN communication on the now missing module.
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Old 05-20-2015, 08:36 AM   #3 (permalink)
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Yeah, if you're wanting to do EOC, you're not going to want the push button start. I'm sure you can probably wire around it, but it'll be a hassle.

Also, if you're doing that much EOC, you definitely do want a kill switch.
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Old 05-20-2015, 12:18 PM   #4 (permalink)
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I don't get why you would need to hit the brakes to start the engine. I try to coast to a hill spot, roll a way and bump start.
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Old 05-20-2015, 02:43 PM   #5 (permalink)
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Fortunately, the brake does not need to be pressed on manual transmission Subarus, it's just clutch in + push button to start, not too complicated. Apparently bump starting is possible but the car really doesn't like it and lights up the dashboard, and I prefer to use the starter.

It appears the engine can be killed while the car is moving by 3 presses of the button which is less convenient than a kill switch but not too inconvenient. So the remaining question is does the car do anything funny if you try starting it while it's rolling.

I think I figured out the engine on -> ACC problem, wiring a capacitor into the accessory relay coil circuit should leave the accessories powered for a fraction of a second to hit the button a second time and not kill the power causing the annoying delay.

I don't EOC that much though, so I'll probably be focusing my efforts on ECU tuning to maximize highway mpg. I'm hoping that with 12.5 compression ratio the engine can be tuned to idle lower than normal...

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Old 05-20-2015, 08:09 PM   #6 (permalink)
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Quote:
Originally Posted by serialk11r View Post
Apparently bump starting is possible but the car really doesn't like it and lights up the dashboard, and I prefer to use the starter.
My Renault will do the same if you just let out the clutch while moving. In fact the ECU will shut off the engine all together and you have to key off and restart to reset it. However, it still bump starts fine with the double clutch method
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Old 05-21-2015, 06:04 PM   #7 (permalink)
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There are eBay kits to add push start, there must be one to remove it?
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Old 05-22-2015, 03:25 AM   #8 (permalink)
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Quote:
Originally Posted by Arragonis View Post
There are eBay kits to add push start, there must be one to remove it?
Heh, no keyhole, no key! Keyless entry. I thought about it and realized it's kind of a nice feature when you're carrying groceries.

If I had my way, it would be like a race car where you have a toggle switch for ignition and power, then a button for the starter, but I don't want to figure out the car's wiring and mess with a newish interior. Or the Honda S2000 arrangement, where the key controls the power and the button activates the starter.

On a side note, I just realized blending 87 gasoline with E85 up to 20% alcohol (7.5 parts to 1) would give ~92 octane gas for 1.5% more per mile cost than straight 87 according to some research I found. Buying 91 (required) would be 5-6% more money than 87. Savings!
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Old 05-22-2015, 04:26 AM   #9 (permalink)
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I've bump-started push-button cars after EOC'ing. It's a bit more complex, depending on whether they'll turn all the way off when you press the button or whether you can put them in ACC or ON mode with the three-press thing.

Add me to the "put in a kill switch" votes.
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Old 05-22-2015, 05:59 AM   #10 (permalink)
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These geeky features such as a push-button start are not meant to eco-driving. Go for a kill switch.

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