Fuel inertia switch issues

Hi everybody, I have a question to pose:

My 97 has this strange issue whenever I put gas in it. It'll run just fine until the next time I try to start it, then it just cranks without firing up. I know the Ex was in a rear end collision so I unhooked the inertia switch for a few seconds and that remedies the problem until I refuel it. Also I remember the reset button on the switches I've fiddled with in the past being pretty prominent, whereas this one doesn't seem to have a button to press (stuck down?).

I plan on replacing the switch, along with the gas cap (cracked o-ring). Will this fix the problem I'm having, or is there something else I need to look for?
Thanks

the inertia switch is like a circuit breaker that's triggered by shock/impact. when triggered, it cuts off the power to the fuel pump. if resetting it (which shouldn't be necessary unless you're in an accident) allows you to start the engine then you can try replacing it, although i don't see why it should be necessary to do this repeatedly. it's not really an electrical device. i think the problem might be your fuel pump. i've had fuel pumps that would work only if you turned the key on/off repeatedly and the real problem was that the fuel pump was worn out.

Thank you. Are there any other indicators I should look for to tell me if my fuel pump is going?

koda2000 said:

the inertia switch is like a circuit breaker that's triggered by shock/impact. when triggered, it cut off the power to the fuel pump. if resetting it (which shouldn't be necessary unless you're in an accident) allows you to start the engine then you can try replacing it, although i don't see why it should be necessary to do this repeatedly. it's not really an electrical device. i think the problem might be your fuel pump. i've had fuel pumps that would work only if you turned the key on/off repeatedly and the real problem was that the fuel pump was warn out.

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I think you meant to say is *IS* an electrical device. When tripped, it interrupts the voltage to the fuel pump. It's basically a circuit breaker that is tripped by inertia, rather than an over-current condition. They do go bad. Mine tripped once by lowering the truck too quickly off the floor jack.

If the button on the inertia switch is "popped out", and a frequent reset is required, my bet is the truck is being subjected to some extreme driving, or (more likely) the inertia switch is failing. Before you change it, inspect the condition of the wiring. If there is corrosion or an otherwise bad electrical connection, the act of moving the switch might be enough to improve the connection and it could be as simple as a bad connection.

pmonahan said:

I think you meant to say is *IS* an electrical device. When tripped, it interrupts the voltage to the fuel pump. It's basically a circuit breaker that is tripped by inertia, rather than an over-current condition. They do go bad. Mine tripped once by lowering the truck too quickly off the floor jack.

If the button on the inertia switch is "popped out", and a frequent reset is required, my bet is the truck is being subjected to some extreme driving, or (more likely) the inertia switch is failing. Before you change it, inspect the condition of the wiring. If there is corrosion or an otherwise bad electrical connection, the act of moving the switch might be enough to improve the connection and it could be as simple as a bad connection.

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i meant what i said. it is not an electrical device, unless you consider a wall light switch an electrical device (i don't). my definition of an electrical device is something that uses the power supplied to it, not just allows power to pass through it or not. jmo. the OP might as well try replacing it before looking elsewhere for the problem, but i don't see where merely putting gas in a vehicle should trip the inertia switch.

Next time it doesn't start, smack the bottom of the fuel tank with a soft faced hammer. If it starts, fuel pump bad. Most likely.

koda2000 said:

i meant what i said. it is not an electrical device, unless you consider a wall light switch an electrical device (i don't). my definition of an electrical device is something that uses the power supplied to it, not just allows power to pass through it or not. jmo. the OP might as well try replacing it before looking elsewhere for the problem, but i don't see where merely putting gas in a vehicle should trip the inertia switch.

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I not sure how to respond to that. I'm trying to help the OP understand what's going on with the switch and the vehicle. I'm not trying to be snarky, so let me say politely and with the best of intention that switches, circuit breakers and relays are all electrical devices. You are correct that Switches and Breakers do not consume power, but they are still electrical devices.

The inertia switch is an electrical switching device (circuit breaker) that interrupts the flow of electrical current when excess inertia is sensed. 12 Volts of Direct Electrical Current is provided to one terminal of the device and passes through the normally closed circuit to the other terminal, unless tripped. With the ignition "On", 12V will be present from negative ground to each of the two terminals. If one terminal or the other has no voltage present, then the inertia switch electrical circuit is open; either because it's tripped or defective. In that case, the current to the fuel pump (or fuel pump relay) is then interrupted.

The OP states that disconnecting the Inertia Switch remedies the problem until the truck is refueled. I can see where *RE* Connecting would remedy the problem, but DISconnecting should interrupt the circuit, preventing the truck from starting. The OP also states that the reset button does not pop out. Perhaps Red 97 could provide clarification.

If it were my truck, I'd measure the voltage from chassis ground at each terminal of the Inertia Switch to see if it's functioning.

like i said (jmo) Just My Opinion. your are entitled to yours. i'd be very surprised if the inertia switch turns out to be the OP's problem, but anything is possible. i just can't understand an intermittent inertia switch problem which is somehow initiated by refueling.

Thanks everyone for the replies. I looked at the switch again and it appears the button is not popping up, which is why I disconnected and reconnected it (couldn't find the button in the dark last night). The wiring harness into the switch looks cherry, no blackened wires or connections. The reason I suspected the switch is because the truck was in a collision and I didn't know if that would be enough to make the switch go bad. I also wasn't sure if something else in the fuel or electrical systems could be tripping it.
I had already ordered the switch before checking back here, so I'm gonna replace it and see how things go. I think I'll also keep a mallet on hand to check if the pump's bad but I hope not.
Thanks again.

inertia fuel shutoff

According to a note on the wiring diagrams the inertia fuel shutoff: "A safety device that cuts power to the Electric Fuel Pump if a collision occurs. Switch must be reset manually." Volvo was one of the first vehicles to have a similar device installed in vehicles but it was a roll over cutoff switch. According to my Haynes Repair Manual the inertia fuel shutoff will not allow electricity to flow to the fuel pump if power to the shutoff is removed. Sometimes removing and reconnecting power will trigger the shutoff and the reset button must be pressed. I question the validity of the second statement since power is removed and restored every time the ignition is switched off and then on.

RED 97 said:

Thank you. Are there any other indicators I should look for to tell me if my fuel pump is going?

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not really. sometimes they will just quit and that's it, often they will work intermittently for a while. the last one i replaced seemed fine until the first cold morning. then i'd have to turn the key on/off until i heard the pump prime. then it would be fine for the rest of the day. hitting the rear bottom of the tank would also get the pump to run. changing the pump was actually pretty easy, but i didn't have any rust to deal with on that vehicle.

And don't forget, the voltage drops after a couple seconds if the engine is not started. So, there is NOT always 12 V going through the inertia switch unless the engine is running.

Update!

Well, it's been a couple of months now and I find myself right back at square one. I've gone ahead and replaced the inertia switch and fuel pump relay, and the truck ran fine for over a month before it started acting up again. I tried smacking the bottom of the tank with a mallet and that seemed to jar the pump back into action. So I replaced the fuel pump and thought the problem was fixed. Then yesterday I had two failure to starts, both remedied by disconnecting and reconnecting the inertia switch. I'm at a loss as to what to do next.

Coincidence?

I can't think of any reason that disconnecting and reconnecting the inertia switch connector (while the ignition switch is in Off) would cause the fuel pump to start running. The PCM monitors the voltage to the inertia switch but only when the ignition switch is in Run or Start. Is it possibly just a coincidence that the engine starts after fiddling with the inertia switch connector?

Which engine do you have in your Sport (OHV or SOHC V6)?

What are your no start symptoms? Does the starter crank the engine but the engine doesn't run? If so, have you tried cycling the ignition switch from Off to Run three times before cranking the starter? That gives the fuel pump more time to build pressure at the fuel rails. Maybe your fuel filter is clogged and it takes time for the pressure to build.

Have you tested the fuel pressure? Maybe the fuel pressure regulator is faulty. Or maybe there is no fuel pressure problem now and something else is the problem. See Ford Explorer Ranger Fuel pressure test procedure

I've got the 4.0 SOHC. The symptom is the starter will crank the engine but the engine won't start The key was in the off position whenever I messed with the connector to the inertia switch. I have not tried checking fuel pressure yet, I'll have to get a pressure gauge to keep in the vehicle for the next time it does it.
Also, my inertia switch has three wires going into it: power in, power out to fuel pump, and a third one that redirects power when the switch is tripped. Where does this wire go, and I wonder if that might have something to do with it?

Edit: I searched on google and supposedly that wire isn't used for anything, but I could almost swear it gets power when the switch is tripped (opened up my old one and looked at it)

I would take a very close look at the inertial switch
connector plug. Even though the terminals look good,
I suspect one is losing connection.

inertia fuel shut-off wiring

According to my Haynes 1997 wiring diagram the inertia fuel shut-off switch has three contacts but only two wires connected to it. The DK GRN/YEL wire comes from the fuel pump relay and the PNK/BLK wire goes to the fuel pump. My 2000 Ford Wiring Diagrams show the same thing. The connector (C203) has three terminals (pins). There is no drawing of the connector in my wiring diagrams. I found a photo of one on ebay and it looks like there are only two pigtails.

However, this photo of one on a 2001 E150 shows more wires.

I plan to install an electronic fuel pump controller in that near the inertia switch.

I'll check my switch connector in a day or two and see how many wires I have.