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Michael Crimp
Tinkerer
QUEENSLAND
V8 UZZ32

Posts: 93
Reg: 06-2008

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Saturday, November 01, 2008 - 05:05 pm, by:  Michael Crimp (Zen1953) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Reverse thread
The Myth Buster guys tried putting an automatic car into reverse in many different ways on a couple of different cars and found there are preventions built in to the box - i.e. It could not be done.
Cheers
Matthew Sharpe
Goo Roo
North Island
JZZ31

Posts: 3857
Reg: 10-2005

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Sunday, November 02, 2008 - 06:46 am, by:  Matthew Sharpe (Madmatt) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

True, I remember that episode, and they were working with a very primitive 80's or early '90's yank tank too.
Cihan Aday
Moderator
etuner.com.au
JZZ30

Posts: 2736
Reg: 07-2005

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Sunday, November 02, 2008 - 06:19 pm, by:  Cihan Aday (Cihan) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

The injectors switch off when you're coasting in 1st, 2nd, 3rd and O/D, true fact for most fuel injected cars..
Spencer Cameron
Tinkerer
NSW
JZZ30 (converted Manual)

Posts: 7
Reg: 04-2008

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Sunday, November 02, 2008 - 08:42 pm, by:  Spencer Cameron (Switchio) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

I'm no mechanic, but wouldn't the engine lean out and melt with no fuel going through it and all that load?
Spencer Cameron
Tinkerer
NSW
JZZ30 (converted Manual)

Posts: 8
Reg: 04-2008

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Sunday, November 02, 2008 - 08:51 pm, by:  Spencer Cameron (Switchio) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)


Spencer Cameron wrote on Sunday, November 02, 2008 - 08:42 pm:

..no fuel going through it and all that load




My bad, i saw engine braking instead of coasting. Still, same problem, just not as extreme.
David Vaughan
Goo Roo
ACT
V8 Ltd manual

Posts: 3985
Reg: 07-2005

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Sunday, November 02, 2008 - 08:51 pm, by:  David Vaughan (Davidv) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

No. You assume there is a lean explosion but what is there to spark? Zero injection = zero fuel = zero combustion.

However, in neutral at idle, fuel is required to turn the engine over, there being no mechanical drive to do the job for you. That is, the coasting theory is a crock even though the result will be little worse than coasting in gear.

See also my posts 3970 and 3971 to which Cihan is here adducing specific evidence rather than my generalised knowledge.
Spencer Cameron
Tinkerer
NSW
JZZ30 (converted Manual)

Posts: 9
Reg: 04-2008

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Monday, November 03, 2008 - 04:50 pm, by:  Spencer Cameron (Switchio) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

I cant speak for auto ecu's, but i've never seen injector duty drop below idle levels (about 5% when hot) in my soarer.

Not during engine braking or coasting (in any gear)
Cihan Aday
Moderator
etuner.com.au
JZZ30

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Monday, November 03, 2008 - 11:52 pm, by:  Cihan Aday (Cihan) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

If your throttle position sensor is working and aligned as it should be, when the throttle is lifted off above 1500rpm or so the ECU will cut injection to save fuel. When you're coasting / engine braking (same thing, no?) - the wheels are turning the transmission which is rotating the engine. No fuel is necessary, we're running on potential energy baby!

Its called deceleration fuel cut, or deceleration enleanment. Nothing special or new, has been used since electronic injections wide spread inception in the 80's.

Melted pistons occur when piston dome temperatures get too hot and stay that way prolonged periods of time and there is sufficient cylinder pressure to take advantage of the piston materials weakened state. Under vacuum / light load - combustion pressure is minimal. Cylinder and piston temps are minimal.

If it was detrimental we'd all have blown engines from hitting boost or rev limiters. Both limiters are achieved by cutting power to the injector circuit!

Imagine that, 20psi of boost, 7,350rpm and suddenly NO FUEL.



On that note, in very high powered applications high RPM's fuel cut isn't the best idea for *repeated* use. Hitting boost or RPM limiters during hard acceleration isn't good for your engine mounts either.
Michael Keen
Goo Roo
nsw
Soarer TT

Posts: 1009
Reg: 10-2007

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Tuesday, November 04, 2008 - 06:12 am, by:  Michael Keen (Spoilt) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)


Cihan Aday wrote on Monday, November 03, 2008 - 11:52 pm:

On that note, in very high powered applications high RPM's fuel cut isn't the best idea for *repeated* use. Hitting boost or RPM limiters during hard acceleration isn't good for your engine mounts either.




oooo but the 1j sounds so nice at rev limiter heheh pop pop pop.. much better then them nissan's
Spencer Cameron
Tinkerer
NSW
JZZ30 (converted Manual)

Posts: 10
Reg: 04-2008

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Tuesday, November 04, 2008 - 10:59 am, by:  Spencer Cameron (Switchio) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)


Cihan Aday wrote on Monday, November 03, 2008 - 11:52 pm:

If your throttle position sensor is working and aligned




Working fine, thanx for asking.


Cihan Aday wrote on Monday, November 03, 2008 - 11:52 pm:

When you're coasting / engine braking (same thing, no?)





No, coasting, as i understand it, is a state in which the car is in a high enough gear that the engine only has to idle to keep pace. Thereby not applying any accelerative or deccelerative forces on the gearbox.

Note the use of the word IDLE, its kinda
important..


Cihan Aday wrote on Monday, November 03, 2008 - 11:52 pm:

If it was detrimental we'd all have blown engines from hitting boost or rev limiters. Both limiters are achieved by cutting power to the injector circuit!

Imagine that, 20psi of boost, 7,350rpm and suddenly NO FUEL.




It IS bad for your car to bounce off fuel cut, ask any tuner. In drag racing the car is expected to perform for such a short length of time that u can get away with just about anything. Drifters, on the other hand, tend to go through engines like toothpicks if they spend a lot of time on fuel cut.

That's why they invented IGNITION cut as well. I assume the only reason its not used in road cars is emission laws.
Ben Richardson
Tinkerer
NSW
V8 UZZ31 GT-L

Posts: 62
Reg: 03-2007

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Tuesday, November 04, 2008 - 01:44 pm, by:  Ben Richardson (Ben_richo) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)


David Vaughan wrote on Sunday, November 02, 2008 - 08:51 pm:

That is, the coasting theory is a crock even though the result will be little worse than coasting in gear.




David, its not a theory, for several weeks now I have been coasting and as stated I have gained approx 50 - 80ks per tank extra. Since owning my soarer (about 8 months) I have monitored fuel usage on every tank. Unless someone is slipping some extra fuel in my tank when im not looking I cant explain where the added efficiency is coming from other than from reduced revs by coasting in neutral when feasible.

After speaking with a mechanic friend of mine, it is true that the injectors cut fuel when coasting in gear, but this seems irrelevant as I had been making the same trip for a couple of months without coasting with the lower efficiency.
David Vaughan
Goo Roo
ACT
V8 Ltd manual

Posts: 3988
Reg: 07-2005

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Tuesday, November 04, 2008 - 01:57 pm, by:  David Vaughan (Davidv) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

I guess it depends how steep is the hill. If coasting allows you to run where otherwise you would need some throttle to stay with the traffic or to pick up speed at the base, then coasting in gear will not be "fuel off" and coasting in neutral more efficient. I am imagining circumstances where your speed is not brought below normal levels by coasting in gear.

I still don't like it on safety grounds even where the hill is shallow enough for in/out of gear to make a difference.
Cihan Aday
Moderator
etuner.com.au
JZZ30

Posts: 2744
Reg: 07-2005

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Tuesday, November 04, 2008 - 04:29 pm, by:  Cihan Aday (Cihan) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Spencer, Toyota 1JZ / 2JZ ECU's manual or automatic use deceleration fuel cut. Its a fact. One of the main reasons i come across this feature not working (when tuning cars, mind you) is the throttle position sensor. If the tps is not relaying an output below the ECU's 'no throttle' threshold there is no decel fuelcut.

If you confirm the minimum and maximum output voltages of your TPS, i'd be glad to let you know if that's your problem.

The problem with high powered, high RPM hard fuel or ignition cuts is the cut period - Usually it is not long enough making the act of limiting RPM a violent one. A 600hp engine might hit a 7,000rpm hard fuel cut 10-20 times a second if you let it, which is hard on internals (bearings, rods and crank).

FYI - The series one 1JZ vvti uses a soft ignition limiter with timing retard, series two uses soft ignition cut, timing retard and throttle control as a limiter, as does the 2JZ vvti. They're progressive / soft RPM limits that aren't violent or obtrusive to the engine or driver.

Lighten up chief.

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