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Old 09-14-2008, 10:53 PM   #21 (permalink)
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How are you all determining when your injectors have stopped firing? Are you going by the cutoff feature in the Scangauge? Or have you wired up LED indicators? I'm still very curious about this. I'm not convinced that my car does this, but I can set the "fuel cutoff" setting in the SG according to the manufacturer's instructions and see cutoff indicated by "9999MPG" under certain coasting conditions. But as best as I understand it this is just a guess. On the other hand, one of my manufacturer-specific X gauges is fuel pulse width, and I never see this register zero under any coasting conditions. Thoughts?

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Old 09-14-2008, 11:07 PM   #22 (permalink)
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The mpguino reads all 9s when fuel is cut. But long before having that, I could tell when mine cuts the fuel. It feels different. The exhaust note disappears. And when I tried an O2 sensor monitor once, it shows nothing when the fuel is cut.
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Old 09-14-2008, 11:20 PM   #23 (permalink)
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You could wire an LED with a 470 Ohm series resistor directly across a fuel injector. The LED would light up to its full brightness whenever the injector is NOT firing. It will be progressively dimmer when the injector is injecting larger amounts of fuel.

Better yet, connect a voltmeter directly across the injector's two wires. Turn on your key but do not start the motor. Read the voltage. This is the full source voltage when the injector is NOT firing. Now start the motor and notice that this voltage will drop and drop further when you are accelerating (using more fuel).

Anyway, when driving, coasting, etc. just look at that voltage. If it reads the same as the key-ON, engine-OFF voltage then you know that your engine is not using fuel.

EDIT: I have that a bit backwards... If the key is ON but the motor is not running, the voltage measured across the injector will be zero volts, not full source voltage. My above numbers would be correct if you wired the voltmeter the way I did to my vehicle, which was to connect the meter between circuit ground and the switched side of the injector (not the powered side of the injector). Same applies to the LED circuit.

Last edited by Gregte; 09-14-2008 at 11:27 PM..
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Old 09-15-2008, 12:36 PM   #24 (permalink)
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I know my tbird cuts fuel until it drops to 2000 rpms coasting, not sure about the festiva though, Im gonna guess lower rpm, as its a total economy car and has much more usable low end power.
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Old 09-15-2008, 05:48 PM   #25 (permalink)
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Since Dane-ger said he had carbs, not fuel injection, it reminded me of what another member of my car pool once did (this will give away how old I am!).
He had a 1956 Ford with the 312 T-bird engine. On a couple of downhill stretches on our commute he could flip a switch to a valve that let outside air into the intake manifold, and that killed the flow of air through the carburetor. Supposedly this saved gas, but I wonder what kind of damage this might have done to the engine, plus the engine cooled too much on long downgrades.
He had an automatic transmission--no lockup in those days-- but the engine kept turning. Maybe the early Ford automatics had a rear pump like the early Mopars did that allowed this to happen.
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Old 06-24-2009, 05:50 AM   #26 (permalink)
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if you have to have power full time power steering - go electric!
one of my diesel rabbits has 4 additional vacuum tanks i can do reeeeeeeally longs hills
that way...
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Old 06-24-2009, 10:40 AM   #27 (permalink)
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I changed over steering to manual and brake booster to electric for coasting (and elimination of engine belt drains).
(If I don't need power steering in my giant truck, nobody does)

But on long steep descents I really want to be able to engine brake to preserve the brakes.

This was easy for me, because I have a diesel.
The engine kill switch I already installed on the shifter cuts off the electric fuel pump. All I have to do is hold it down for as long as I want to engine brake. A couple jobs in the hills past couple days, used this feature a whole lot.
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A few months ago I returned home just as my neighbor pulled into his driveway. It was cold (around freezing) with some rain and sleet, and he yells to me: You rode your bike? In this weather?!?

So the other day we both returned home at the same time again, only now the weather is warm, sunny, with no wind. And I yell to him: You took the car? In this weather?!?
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Old 06-24-2009, 12:38 PM   #28 (permalink)
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Originally Posted by MetroMPG View Post
That's one area I'm less familiar with (I rarely drive an automatic). I suspect they can only fuel cut when the torque converter is locked, otherwise the engine would stall out.
Not necessarily, my father's Bravada will cut if I shift down to 2, and EB down a hill at 25-30 mph. I do not know if it's locking the converter or not, though.
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Old 06-24-2009, 01:26 PM   #29 (permalink)
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Quote:
Originally Posted by Formula413 View Post
How are you all determining when your injectors have stopped firing? Are you going by the cutoff feature in the Scangauge? Or have you wired up LED indicators? I'm still very curious about this. I'm not convinced that my car does this, but I can set the "fuel cutoff" setting in the SG according to the manufacturer's instructions and see cutoff indicated by "9999MPG" under certain coasting conditions. But as best as I understand it this is just a guess. On the other hand, one of my manufacturer-specific X gauges is fuel pulse width, and I never see this register zero under any coasting conditions. Thoughts?
I can't tell if my father's truck does it or not, the 2.2L doesn't have much back torque to begin with. But on his Bravada, it's very noticeable when the engine stops receiving fuel. It also has a factory gauge, which hits 99mpg when the injectors stop.
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Old 06-24-2009, 01:31 PM   #30 (permalink)
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Quote:
Originally Posted by fud2468 View Post
He had an automatic transmission--no lockup in those days-- but the engine kept turning. Maybe the early Ford automatics had a rear pump like the early Mopars did that allowed this to happen.
Ray Mac.
Pretty much anything prior to the 60's had rear pumps, and most from the 60's did, too. But even without a rear pump, there's enough pressure built up in an automatic going at speed that it won't drop the motor until you get to a very low speed.

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