Inertia switch - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 01-21-2015
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Inertia switch

Trying to troubleshoot my vehicle's fuel pump, I first tested the inertia switch and found it OK. One wire goes straight to ground, while the other, I think, goes to the pump's positive terminal. Also found at the wire 12v. for about 2 secs. when the ignition is turn on.

On the other wire, I read 2.5Kohms for what I thought was the fuel pump's coil. Is the reading too high and the fuel pump should be replaced?

Question: Can anyone point me in the right direction? what reading should I get
at the pump's coil? Are my assumptions correct?.

Thanks,

Raz45
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Old 01-21-2015
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You can't really get a reliable OHM test on the fuel pump motor or any electric motor via it's power wires, if you take the motor apart you can test the coils.

Pretty simple test is to just give the pump 12volts, if you did the OHM test you already have access to the correct wires.
If pump comes on it works.

Inertia switch just has 12v IN from fuel pump relay, and 12v OUT to fuel pump, no Ground.
Fuel pump's Ground wire is often located near the inertia switch, if that is what you meant.

And if you have 12v for 2 second at inertia switch and fuel pump is not coming on then fuel pump is the problem, for sure.
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Old 01-21-2015
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Hello RonD,
I brought a 12ga. ground wire bolted onto bare metal at the engine compartment and into the cabin (no good ground inside the cabin). If there is a diode inside the pump to prevent reverse polarity voltage applied to the pump maybe I'd get an open reading. I'm trying to avoid removing the gas tank(for the 4th time) just to inspect the fuel pump.
What's your suggestion?
Thanks.
Raz45
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Old 01-21-2015
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Ground for cab should be from engine head to firewall, but you can't have too many Grounds.

Best way to check fuel pump is to give it 12volts, it either works or is doesn't.

Ford fuel pumps generally last 20-25years, surprised original pump failed, but that being said the newer pumps, 2000 and up seem to have a higher failure rate.
You can usually find Motorcraft pumps for much less than dealer pricing, but still not what I would call cheap.

There are quite a few stories about other brands of fuel pumps that fail in 1 to 6 months, under warranty but still a pain to replace.

I think Motorcraft fuel pumps have 30 day warranty, lol.
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Old 01-22-2015
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Inertia Switch

Hello Ron,
Thanks for the observations.
It's difficult to be working on the electrical inside the cabin and simultaneously, listen for the humming/priming noise at the fuel tank. I'll get me an assistant next time.

One of the times that the fuel pump was mistakenly replaced, it was really a pats problem. I had to remove any metal objects, such as a metal key ring from the key, use only one key to turn the ignition on(no second key dangling on the plastic key ring). Have to have a free transponder system between ignition-antenna switch and the transponder key.
My next trip to the US, I will purchase: Haynes Repair manual, OBDII code scanner/reader(I had one but I can't find it) a Timing light, and couple of fuel filters. In the meantime, the broken truck is blocking my garage.
I'll do some more electrical test, and probably end up changing the fuel pump once again.

Thanks,

Raz
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Old 01-23-2015
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Ranger fuel pumps are not quiet, if engine isn't running you can hear them easily from inside the cab, .........if the radio is turned down, lol.
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