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fuel pump resistor ohm reading...

Old 08-08-07, 10:34 AM
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fuel pump resistor ohm reading...

I am checking the fuel pump resistor to see if this is my cause for the problems. The manual says that the resistance between the 2 prongs on the connector should be 0.5 - 0.7. Mine is reading 0.9 on the 200 ohm scale...would this be far enough out of whack to warrant replacing it?

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Old 08-08-07, 05:14 PM
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Current draw at 12 V at .7 (outside reading) is 17 amps

Current draw at 12V at .9 (your reading) is 13ish amps....

That is a lot less current, and should lead to worse performance....

I would replace it personally as fuel is not something to be taken lightly
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Old 08-08-07, 06:32 PM
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i found that at idle, and under light load of driving, my fuel pump is producing 8.9-9.4 volts...should I do the re-wire AND replace the resistor?

Trev
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Old 08-08-07, 06:35 PM
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for one thing your fuel pump doesnt produce voltage. and for another, the entire function of the fuel pump resistor is to lower the current to the pump during idle and light load conditions. this makes the pump spin slower and saves wear. the resistor is switched out of the circuit under high load conditions so the pump recieves full voltage. so its fine leave it alone and just make sure the fuel pump speed relay is working correctly.
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Old 08-08-07, 10:22 PM
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right, sorry for the mis-verbage. Fuel pump speed relay...are you just referring to the fuel pump relay in the fuse box at the nose of the car? Yes, that is functioning. So, you are not advocating the fuel pump rewire to get the extra volts to the pump?
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Old 08-08-07, 11:18 PM
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it runs on 2 circuits. theres one relay to turn the pump on, and one to control the speed by switching the resistor in or out of the circuit. feel free to rewire the full speed circuit if you think you need to (mostly a waste of time) but leave the low speed alone. make sure the second relay (the speed control) is working and not keeping the pump running through the resistor all the time.
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Old 08-09-07, 10:05 AM
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where is the speed control relay? I understand where the relay at the front of the nose is located...is that just the one to turn the pump on?

Trev
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Old 08-09-07, 12:51 PM
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Here are the locations:
Attached Thumbnails fuel pump resistor ohm reading...-solenoid_relay_location.jpg  
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Old 04-15-12, 01:27 AM
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I know it's an old thread, but I'd like some clarification.

Based upon what Mahjik posted, and looking at the wiring diagram (Section Z: B-1a), it is my understanding that the Circuit Opening Relay (located in the X02 Relay & Fuse Box) triggers the low-speed circuit via the Fuel-Pump resistor

It is the ECU that triggers the high-speed circuit via the Fuel-Pump Relay located near the FRONT bumper.

Please correct me if I'm wrong.

Lastly, my fuel-pump is out of spec, also at 0.9 ohms on my Fluke.

Do I need to get a new one ?

Thanks,
:-) neil
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Old 04-16-12, 11:56 PM
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I haven't personally checked these sections of the OEM wiring harness, but what I'm seeing in the Mazda diagrams matches what you've described.

In low-speed mode, power to the fuel pump goes through the ignition key, then through the 20A fuel pump fuse, then through the Fuel Pump Relay, then through the fuel pump resistor, then to the fuel pump.

In high-speed mode, power to the fuel pump goes through the ignition key, then through the 20A fuel pump fuse, then through the fuel pump relay, then through the Fuel Pump Speed Relay (bypassing the fuel pump resistor, since the relay is wired in parallel), then to the fuel pump.



The ECU controls both the Fuel Pump relay (pin 1T), and the Fuel Pump Speed Relay (pin 1K).


One thing to note: when trying to measure very low resistance values you should remember that the multimeter probe wires have some resistance to them also. Try connecting the black lead to the red lead (without anything else in the circuit), most meters will usually measure 0.2-0.8 ohms.
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