Frequency Counter as FE Meter? - Page 2 - Fuelly Forums

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Old 11-28-2007, 05:11 PM   #11
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A simple low-tech way to measure relative consumption would be to build a circuit that drives a meter or a lamp off of a capacitively charged circuit that gets it's input off of one of the injectors. Obviously faster or longer pulses will convert to more throw or lighting of the meter.

So I guess it would be injector signal->diode (to keep the capacitor charge from going back through to the injector)-> resistor 10K or so ( to keep the circut from draining the injector signal too much) capacitor to ground parallel with anonther resistor(capacitor to store pulse charges, resistor to discharge capacitor when pulses get smaller) with voltmeter in parallel with the capacitor and resistor to measure the stored charge?

The amount of time the injectors are open would then be displayed as MV on the meter so you could see if it takes more gas on a hill in 3rd at 1800 rpm as compared to 2nd at 2400
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Old 11-28-2007, 06:26 PM   #12
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That sums it up. Throw in some variable pots to tune it, and you've got something nearly as useful as a Scanguage for realtime FE readout IMO.
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Old 11-29-2007, 12:35 PM   #13
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Thanks Snax, I think an analog meter would be the way to go so it wouldn't jump around though. It would look sharp as a fuel consumption guage

I was doing some thinking though. Wouldn't a True RMS AC voltmeter accomplish the same thing? The shorter the average time the injector is open the smaller the mean voltage.

Duty cycle automotive multimeter looks promising also. Besides a multimeter is always a good thing to have around.

My only other question is where is the best place to steal a signal from an injector on a CRX?
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Old 11-29-2007, 02:01 PM   #14
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The wiring at the ECU connectors probably. It's already in the interior, and the wires are relatively exposed (you won't have to pull off any wire loom). Though at the ECU, you will see a connection to ground when the injector is firing and 12V+ when it's idle.
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Old 11-29-2007, 02:21 PM   #15
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The wiring at the ECU connectors probably. It's already in the interior, and the wires are relatively exposed (you won't have to pull off any wire loom). Though at the ECU, you will see a connection to ground when the injector is firing and 12V+ when it's idle.

Thanks, good deal. I guess with that inverted signal and any metering scheme that would make it a fuel efficiency meter. The duty cycle meter would read 100% when the injectors are shut off and 0% at 100% Duty Cycle?

So I guess this is my new $19.99 scanguage?

http://www.sears.com/shc/s/p_10153_1...ty+cycle+meter
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Old 11-29-2007, 07:47 PM   #16
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If you connect the positive probe to the injector wire and the negative to ground, yes it will read that way.
If you connect the positive probe to a constant (ignition switched really) 12V source, and the negative to the injector wire, it should read properly. When the injector is off, there would be 12V+ on both probes, so no voltage potential between the two and no reading. When the injector gets switched on, the wire would flip to ground, causing the meter to see a 12V potential. All you're doing is hooking up the meter in a similar manner to the fuel injector: Constant power on one side of the coil, switched ground (the ECU) on the other.
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