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Old 01-24-2007, 05:53 PM   #41
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It's not pumping losses, just engine friction. I asked a similar question at the end of this post and got this response...
Quote:
I tried it in my car. The deceleration time, in gear, with the ignition off, was identical whether I had the throttle open or closed.
Pumping losses only have with combustion, especially in gassers.
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 01-24-2007, 06:22 PM   #42
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BeeUU -

Quote:
Originally Posted by BeeUU View Post
I have a question about the kill switch use:

In order to eliminate the "bump" start could you:
1 Kill the injectors
2 leave the engine engaged
3 open the throttle fully to reduce pumping losses/alt still charging (REGEN BRAKING?)
4 finishing coasting but still be in motion (rpm about 1500)
5 close the thottle while still rolling
6 start the injectors

The bump will be removed....saving a tiny bit of clutch material.

Bill
I have the same question for a different reason. Correct me if I am wrong. This is what I was thinking :

EDIT : Re-order the list below

1 Foot off the accelerator
2 Leave the engine engaged
3 Kill the injectors with momentary switch (gotta hold the switch down)
4 Finish coasting but still be in motion (RPM never lower than idle RPM)
5 Start the injectors by releasing momentary switch.
6 Foot on the accelerator

Some cars do a form of this already. When the driver is "coasting in gear", the PCM sees that the throttle is 0, so it shuts off the fuel injectors. It does this until the car slows down to it's idle RPM.

Other cars don't do this or do this to a less efficient degree. From what I can tell on my ScanGauge, my Saturn doesn't appear to do this. I think this is true because when I am "coasting in neutral", I see roughly 3 to 1 MPG to MPH. That is, if I am going 60 MPH in neutral, I see over 180 MPG on my ScanGauge. This is not true when I am "coasting in gear" because the RPMs are so much higher. In that case I think I see maybe a 2 to 1 MPG to MPH.

So, I think there is value in doing this from a *tactical* standpoint where you want to emulate the features of a car that is a better manager of MPG.

Safety Side Benefit : I *think* in this case that you maintain your power brakes and your power steering. This is the real reason I am curious about this.

You aren't getting the MPG of coasting with the gas off, but it may be better than what the drivetrain is doing right now, and it may be tactically smart in high-density/aggressive driving conditions.

CarloSW2
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Old 01-25-2007, 02:47 AM   #43
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Originally Posted by thisisntjared View Post
since my car was stolen i redid a good chunk of wiring around my relays. so now i have a kill switch and i remove one of the relays.

i refuse to give specific online. i am sure most of you understand. anyway, i use it for security, not for engine off coasting.
I just had somebody do mine then I relocated it to a different location. I have over $400 in security stuff on my car. It's not the fact that the car will be stolen that irritates me but the fact that finding another car and paying title&registration is a huge hassle.
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Old 01-25-2007, 08:54 AM   #44
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My VW and Peugeot both cut fuel when I lift and coast, but with the throttle closed the car decelerates. I was hoping that with a injector cut I could open the throttle and coast. I did not think the friction would be that great. But I guess the alternator and PS/H20/oil pumps are dragging alot.

Since I am new at this, I will make this one of my first experiments!!!

I guess I still am getting a little of that energy back with the alternator still charging the battery, pseudo brake regeneration.

Thanks everybody for the help.

BTW, are there instructions posted any-where on how to accomplish the injector cut out. I saw the post by skewbe with the huge resistor, I am not sure what that is used for......

Quote:
Originally Posted by skewbe
The injector resistor is HUGE (purple circle), I'm a little concerned about my little switch. But I have an alligator clip and can jury rig the leads back together if necessary A relay would provide more peace of mind, but cei la vie. I'll keep an eye on the mileage. Last tank sucked.
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Old 01-25-2007, 10:56 AM   #45
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It was simple enough on the metro since it only has one injector (TBI). Since the injector resistor was in series (according to the schematic) with the injector, I just added a switch in series with one of the leads going to the injector resistor. Presumably the resistor is there to limit the current going to the injector.

It hasn't thrown any codes that I have detected on the metro.

I don't have a step-by-step guide, each car is possibly different and you have to look at the schematic and decide where to put the switch, electronically speaking. I've deemed describing how to physically install a switch and how to run wires as being out of scope
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Old 01-25-2007, 11:07 AM   #46
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engine braking v/s coasting

The idea is to go as far as you can without expending any fuel, so avoiding engine breaking IF THE ROAD IS CLEAR AHEAD is the preferred method.

Otherwise it all comes down to timing, i.e. can you slow down enough, but not too much, in 3'rd gear before the light turns green, etc.

Sometimes theres an unexpected turn arrow and you wind up at a dead stop and have to use the starter, other times you were able to keep it in gear for the relight, other times you coasted half a mile without spending any fuel and had just enough momentum left to bump it when the light turned green. It's all good
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Old 01-25-2007, 12:34 PM   #47
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resistor!!!

Oh, the resistor heat sink is an original part, sorry I misunderstood. I though you added that as part of your switch.

Thanks for the clarification.

I was planning on using the existing throttle position switch, and wiring my in cabin switch to make the ECU think I have the throttle closed. Should be fairly clean.
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Old 01-25-2007, 05:44 PM   #48
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Standard disclaimer:

The brakes lose there power boost after an application or two if the engine stops turning, you still have brakes but you have to press a lot harder for the same effect, so get used to stopping without power assist AWAY from other people/cars/backs of garages. It's quite doable, I've had cars that weighed more than twice as much without power brakes, but something anyone installing a kill switch needs to be prepared for and will assume all liability (henseforth known as "duh") for should they turn off their engine whilst moving.

Also if you manage to lock your steering column while moving, then duh.

And if you over allocate your focus on your technique and lose situational awareness, then duh.

And if you stop/slow down on the tracks or other perilous spot and cannot relight the engine, then duh.

And if you critically overspeed going down a mountain, then duh.

And if your modification causes your vehicle to burst into flames, or otherwise affects its longevity, then duh.

And any other case where you might not want to be accountable for your actions, duh.

offer void where prohibited, for entertainment purposes only, employees do not qualify, may cause primisim nausea or potatoe famine, your mileage may vary.
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Old 01-25-2007, 06:01 PM   #49
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Quote:
Originally Posted by MetroMPG View Post
(it occasionally seems to spin an extra rev, half-heartedly, which could be due to the injector providing a last dribble of fuel.)
Ya know, mine still takes a while to die. It seems to stumble and shake a bit right before zero rpm. I'm running a bottle of injector cleaner through it now, will see if that helps.
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Old 01-25-2007, 06:58 PM   #50
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Quote:
Originally Posted by theclencher View Post
affleck (Electrical) 12 Sep 06 15:54
If this guy is right...
Ya know, my scangauge said I was using .2 gal/hr in overrun, but it said that even with the injector disconnected, so I'm not sure I believe it. I'll have to actually measure to see if there is any current going to the injector in overrun. I've seen my scangauge go into open loop during a decent overrun?!?

re throttle open braking, assuming engine is off: If you hold the throttle open, the compression stroke works harder, but as soon as it goes past TDC you have more pressure pushing the piston back down, so you pretty much get the energy back. There will be more pressure pushing the rings out and on the bearings, but nothing like when there is the usual controlled explosion in the cylinder.

re: jake brake, basically it pops open the exhaust valve at TDC on the compression stroke so all that compressed air DOESNT push the piston back down and return the energy to the crankshaft. No 14.7:1 considerations or anything. No throttle on the Diesel anyway and the exhaust valve is not held constantly open, so I'm not sure how right that guy was. However, a jake brake probably would work better with the throttle open/unobstructed.

The jake brake folks themselves diagram the concept nicely:
http://www.jakebrake.com/products/ho...rake-works.php
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