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Old 06-09-2008, 12:27 PM   #11 (permalink)
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I have a 2001 5sp TDI Jetta, and I do a lot of NICE-OFF coasting in my P&G (Pulse and Glide) routine. I have to shut the engine off with the key every coast, and a push-button fuel cutoff would be much easier. Just to make sure I've got an idea of what's going on, the fuel-cut solenoid is normally closed (12 V allows fuel flow) and you used a normally open Push Button wired to a normally closed 12 V relay that is in series with the solenoid for your fuel cut. Is this how you did it/will this work?

Kirk

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Old 06-09-2008, 07:39 PM   #12 (permalink)
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no actually I used no relay to test this. I found the injector harness ground, cut it, and wired in a normally closed switch, so when I pressed the button it killed the injector's ground. Again the car doesnt quite die but it chokes bad @ idle, so it's pretty much instant no fuel. I do not have electronics hooked up to an injector yet so I cant tell you how much juice is going thru, as stated before I might have a second ground, or the actual wires might be their own ground, like the current could be shorting on a 5v lead from a 12v power. Ive never really messed with these things before. I do notice that I'm P&G much more just to be able to use my toy, so the placebo effect and further practice might be much more effective than the button.
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Old 06-09-2008, 10:01 PM   #13 (permalink)
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Thanks getnpsi. I would rather have a normally open switch so if it's lead are somehow detached in the dash, I will lose the choke, but the engine will still run. Which means I need a normally open switch and normally closed relay. Will the wiring diagram in the attached file work? (I forgot to draw it, but the GROUND wire goes to the switch, then to the ground)

Relay: SPDT (OR SPST NC) 12V 1A
Switch: SPST NO, Momentary



Will 12V 1A relay, and 3A 250VAC switch, work for this application?

edit: I'm using it to kill the engine in idle for P&G, not for engine braking, so I need a complete kill.

Thanks.

Kirk
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Old 06-09-2008, 10:18 PM   #14 (permalink)
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re: kill switches, I'm a convert to the ignition type kill switch. I've done the fuel system cutoff and inevitably they stumble on after hitting the switch (even with mpfi). It is better to interrupt the ignition signal from the camshaft/crankshaft sensor.
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Old 06-09-2008, 10:44 PM   #15 (permalink)
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Quote:
Originally Posted by dcb View Post
re: kill switches, I'm a convert to the ignition type kill switch. I've done the fuel system cutoff and inevitably they stumble on after hitting the switch (even with mpfi). It is better to interrupt the ignition signal from the camshaft/crankshaft sensor.
So how long does it take to burn the fuel left on the intake valves? Would keeping the throttle open for an instant longer clean it up faster?
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Old 06-09-2008, 11:02 PM   #16 (permalink)
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Quote:
Originally Posted by dcb View Post
re: kill switches, I'm a convert to the ignition type kill switch. I've done the fuel system cutoff and inevitably they stumble on after hitting the switch (even with mpfi). It is better to interrupt the ignition signal from the camshaft/crankshaft sensor.
Hmm are there any repercussions to doing it this way? I thought it would be 'cleaner' (have less impact on other electronics) if I cut the fuel directly, but that's two people saying it didn't cut the fuel completely. John, have you had problems with the engine not dying completely while in neutral?

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Old 06-09-2008, 11:46 PM   #17 (permalink)
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When I release the switch, the car runs fine and it doesnt stumble at all. This may be because it never really dies completely, however I'm thinking if there is a noticeable stumble and the ecu's trying to catch up it might be dumping fuel and making emissions go up anyway.

Now doing this on a diesel could be easier or maybe even harder...the injectors' pressures aren't any 43psi. I need to pick up that dwell meter toy from harbor freight and get a diagram of my harness. I'm planning on tearing out this engine and want to use the same ecu/harness to power a larger engine, so matching up fuel injectors will be an upfront issue in the future.
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Old 06-10-2008, 12:09 AM   #18 (permalink)
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DJ, et. al. the problem is that there is fuel in the manifold even though you cutoff the injectors. You *can* burn it out faster by holding the throttle pedal open while in neutral, but I prefer leaving it where it is that I might use it for accelerating the car.
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Old 06-10-2008, 12:33 AM   #19 (permalink)
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There is a thread that parallels this idea, the member is using a seperate switch for everything LOL. Anyway he kills the ecu rather than just the fuel injectors. I might try this idea when I get under the hood again. Ill probably keep this fuel injector circuit because its already made, use a vacuum switch and add an ECU cut. I have one on my srt-4 already to reset the computer, but on the aspire ill just use the 12v ignition for the key so it doesnt kill the stored memory.

I never thought of bumping the throttle with the button held down. If i hear an extra sputter then ill know if there is that much fuel left. I'm not goosing throttle when trying to save gas, that naturally never occured to me heh.
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Old 08-19-2009, 11:02 AM   #20 (permalink)
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For those who have a stumbling engine when trying to cut fuel, I would guess that the reason is that not all of the injectors are being cut off. You're essentially running on 3 cylinders (if you have a 4 cyl engine).
On my Focus, there is a single +12v power wire coming from the power distribution box that then splices into 4 separate power wires... one to each injector. The 4 wires that come out of the 4 injectors are then the ground wires that go to the engine control module. The control module "switches" the ground wire in order to control each individual injector. So if your car is like my car, you cannot cut just one ground wire, or you will be cutting only one injector. In my case, I cut the single power wire before it splices into 4 separate wires. I have a normally closed momentary switch attached to the shift lever, and it works beautifully (except that the switch broke today, almost leaving me stranded in traffic). No relays necessary. I found this thread while searching for a source for a more robust NC momentary switch, to replace my broken one.

So my technique is to simultaneously lift the throttle, press the clutch, and press the fuel cutoff switch. I watch the tachometer drop to zero, and then let go of the switch. It does take some time for the engine to spin down to zero, especially if you are traveling at higher speeds. Around 45mph in 5th gear at about 2000rpm requires around one second to kill the engine. 65-70mph at 3000rpm can take around 2 full seconds to spin down, before you can release the switch.
I can tell you that pulse & gliding with the engine off (versus letting it idle while gliding) is definately worth it. Idling at stop lights also destroys your trip average fuel economy. Glide to a stop light with the engine off, leave it off, and when the light turns green then key up and go. I'm getting 55-57mpg in my Focus, and before I wired in the fuel kill switch I was getting 40-45mpg.

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