anyone use a fuel pump kill switch?

[WagonCrazy]

Considering adding in this $20 item to the electronic fuel pump circuit in my restomod Nomad build...specifically to kill the power to the fuel pump relay in the event of a hard crash, rollover, etc.

As its wired now, if I had an accident that resulted in a break of the fuel line anywhere between the tank and the engine, (with the 12v power still on because the key is on)...I'd be shooting fuel out at the rate of about 50 pounds of pressure. Instant fire I think...

Do any of you guys run something like this item to kill the power to the intank pump and stop it from becoming a flamethrower?

https://www.amazon.com/Hotwin-Inertia-Standard-Ignition-Electric/dp/B07RBK4873/ref=pd_lutyp_rtpb_2_3/130-6117220-9473117?_encoding=UTF8&pd_rd_i=B07RBK4873&pd_rd_r=8c4e1f6e-aa92-4d7c-9a9d-e94063504651&pd_rd_w=Gehfo&pd_rd_wg=hBvtp&pf_rd_p=79c338de-db35-45bb-8877-1dfef7993da3&pf_rd_r=XNMAZ8YBVFV2CRV0Y0B0&psc=1&refRID=XNMAZ8YBVFV2CRV0Y0B0

[scorpion1110]

WagonCrazy:

I am admittedly the biggest Ron Francis fanboy in existence. They always have a solution and their parts are top notch.

Here is their electric fuel pump cutoff:

https://www.ronfrancis.com/prodinfo.asp?number=CR%2D92

Its Part Number CR-92.

Its a collision cutoff.

The less expensive way is to use an Oil pressure switch to complete the ground. Once oil pressure dies it effectively kills the pump.

Its not cheap but their stuff is so damn nice.....

[Rick_L]

That kind of switch is of no or little value for an EFI setup since the ecu is going to shut off the pump as soon as the engine isn't running, and an EFI engine won't run long with no fuel pressure. It makes more sense on a carb deal because there isn't anything to shut it off with that system.

[55 Rescue Dog]

It seems like it could be tied into a remote battery-disconnect latching solenoid, and that would kill the whole electrical system if something bad happened. The same solenoid could be also used for a remote disconnect, simply operated by a toggle switch. It would be a good setup even without the crash sensor. That's the disconnect I'm going to use in my car anyway. Can easily find a great place for a toggle/pushbutton switch, instead of trying to route battery cables for easy access to the disconnect. I will also try and do all of the switching/connections on the negative side, to minimize accidental contact points you have using the +plus side. I would also want a small pilot light to know when the system is powered up, since they use a momentary switch on a latching relay, with no indication. Pretty easy system to turn on/off, but also would be easy to accidently power up, especially if using the supplied 2-way momentary toggle switch. I will try and find a more fail-safe solution in addition, like when working on the car for example, which could as easy as just pulling off the negative cable like I've always done, or should have.:eek:
https://www.ronfrancis.com/prodinfo.asp?number=MS%2D21

[55 Rescue Dog]

I really like the products that Ron Francis wiring sells. They are not cheap, and the shipping prices are based on cost, instead of weight just to add to the pain of getting what you pay for, to get good stuff. The wiring harnesses do give you the option of wiring from either direction to the device, which I've found to be a plus too, instead of running all of the wires from one common point from the fuse panel.

[chevynut]

It's so worthless that Fords, Lincolns, Jaguars, and other cars had them for years. I think it's a good idea to incorporate some kind of safety fuel shutoff that doesn't depend on the engine dying to shut off the fuel. If the fuel return line is broken in an accident, the pump could continue to run until the tank is empty. Even a cracked pressure line could spew fuel and the engine could still be left running. Most new cars use the airbag sensor circuitry to stop the fuel pump in the case of an accident. I have an inertia switch from a Jag but it says Ford on it. IMO it doesn't hurt a thing, is simple and inexpensive, and may save your car or your life.

https://rts.i-car.com/collision-repair-news/where-did-the-ford-inertia-switch-go.html

[WagonCrazy]

the inertia switch, it is designed to shutoff the fuel pump in the event of a collision, as to not create a fire hazard if a fuel line is damaged. Inertia from a crash was used to trigger the switch. This worked good for a collision, but the switch would sometimes trigger after hitting a large enough bump, leaving a driver stranded on the side of the road.

So thinking this thru...I should install the switch somewhere where I can get to it fairly quickly, in case I have to manually reset it. I wonder how sensitive these $20 Amazon switches are to road bumps? I would hate to have this thing shutting the pump down in a non hazardous situation. Guess I'll just wire it in at the center console (where the fuel pump relay and fuse is) and take my chances...

[WagonCrazy]

That kind of switch is of no or little value for an EFI setup since the ecu is going to shut off the pump as soon as the engine isn't running, and an EFI engine won't run long with no fuel pressure. It makes more sense on a carb deal because there isn't anything to shut it off with that system.
Huh?

Running or not, when the key is turned to the first position...the ecu sends the 12v signal to the fuel pump relay, which allows 12 volts to got to the pump, which makes it run.
Running or not, as long as the key is in that position, the relay is on, and the pump is pushing 50# of pressure from the back of the car (tank) to the front of car (fuel rail on the LS engine).
If at any point between them...a physical break in the fuel line occurs...the fuel would continue to pump and fire hazard occurs.
Running or not.
As long as the key is in that first (run) position...

[WagonCrazy]

So I just ordered one from ebay.. $10 and change (delivered)...

https://www.ebay.com/i/183727849647?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=183727849647&targetid=539174493035&device=c&mktype=pla&googleloc=9031151&poi=&campaignid=6470648147&mkgroupid=74956728902&rlsatarget=pla-539174493035&abcId=1139336&merchantid=6296724&gclid=EAIaIQobChMIkZy34MG65gIVAcJkCh0UNgMPEAkYByAB EgKu8fD_BwE

I'll wire it up and bench test it before I install it....as I want to know how much inertia it can take before it triggers. Gonna be somewhat unscientific though...as I will whack it with a screwdriver handle, whip it around in the air by its wires, smack it on the bench, etc.

[Rick_L]

Running or not, when the key is turned to the first position...the ecu sends the 12v signal to the fuel pump relay, which allows 12 volts to got to the pump, which makes it run.
Running or not, as long as the key is in that position, the relay is on, and the pump is pushing 50# of pressure from the back of the car (tank) to the front of car (fuel rail on the LS engine).

No. When you first turn the key on, the pump is on and "primes" for a couple of seconds. It then shuts off. It turns on again when an rpm signal is detected from the ignition sensors. If the ignition sensors don't show rpm, the pump is shut off.

The only real question here is how long can an EFI engine run without fuel pressure. Not long at all.

[chevynut]

I'm sure there are LOTS of accidents where the engine keeps running after impact. That's why car manufacturers use impact sensors to shut off the fuel pump. As I said above, you can completely sever a return line or partially sever a pressure line and still have fuel pressure. My in-tank fuel pump is rated at 255 LPH (67 GPH or 1.12 GPM) at EFI operating pressure and that translates to a pretty big leak with the engine idling.

[55 Rescue Dog]

I think the inertia switch is a must have too. In an accident, that could come in very handy, but it's too bad their wasn't a good way to know when you have a simple fuel leak undetected too, until it bursts into flames. That seems to happen a lot! I've been caught more than once with a bad mechanical fuel pump spraying gas right onto the headers. Which you can only see with the hood up, with the engine running, since it instantly burns off. I don't know if it makes a difference, but as far as location I am going to mount my crash switch in the rear near the tank/pump. If it has an extra pair of contacts, I would connect them up to an indicator light, so you know WTH made your car quit running. While I'm at it I will do something on the cooling system to know when you've just dumped all of you coolant on the highway. That's happend to me too many times, and everything seems fine, because the temp gauge don't work heated by air.

[WagonCrazy]

I am going to mount my crash switch in the rear near the tank/pump. If it has an extra pair of contacts, I would connect them up to an indicator light, so you know WTH made your car quit running.

Good thoughts...but since the switch is resettable, i'm not going to bury it...but put it in the center console near all the other wiring so i can get to it. And good suggestion to add a simple led light, to know quickly if it tripped or not.

[chevynut]

And good suggestion to add a simple led light, to know quickly if it tripped or not.

You'll know quickly that the switch tripped because the engine will die.:eek: These switches usually have three contacts, common, NO, and NC but often only two are used. You could wire in a light, but it would only come on when the fuel pump is supposed to be running and the switch is tripped. Running it to a buzzer or chime might be a slicker alternative and you wouldn't have to actually SEE it. Bit then again it might be easier to just remember to check the switch if the car won't start. ;)

[chevynut]

Hey Paul, I'm curious how you ended up wiring your fuel cutoff inertia switch into your fuel pump circuit. It looks like Ford wires them directly in series with the pump. However, I was just ordering new terminals so I could wire mine and I realized it might be better to wire it into the coil side of the fuel pump relay. That way the fuel pump current wouldn't have to run through the switch and potentially cause a voltage drop to the pump. I wonder why Ford didn't wire it that way. :confused:

I think I'm going to put my inertia switch under the rear seat so it's easy to get to, and install an audible device to indicate when the switch is tripped. Hope I never hear it. :p

[WagonCrazy]

It looks like Ford wires them directly in series with the pump. However, I was just ordering new terminals so I could wire mine and I realized it might be better to wire it into the coil side of the fuel pump relay.

I'm wiring mine "in line" with the ECM signal wire -to- coil side of the fuel pump relay. For this same reason (not to have the inertia switch carrying the full amperage thru to the fuel pump).

I found a cheap led light+buzzer on amazon and ordered that.

I'm using that 3rd available pin (in the inertia switch) to energize the light/buzzer (so that when I hear it, and open the center console lid to investigate, i'll quickly see the light on, buzzer buzzin' and can quickly hit the reset switch.

I'll post a few picks when I get it all wired in.

[chevynut]

Sounds like we're thinking alike Paul.:) Looking at my switch it appears that it has a steel ball held in place by a magnet, which holds the switch closed. When the ball is yanked off of the magnet by a shock, the switch opens. Then it has to be manually reset by pushing the ball back into the magnet. I would be sure to mount it vertically as that should help prevent false tripping due to potholes or rough roads. Hope we never have to worry about whether these things work or not.:eek:

[WagonCrazy]

Got the fuel pump shutoff "inertia" switch wired in and working. However, my plan was to use the same signal voltage coming from the ECM to make the little LED light/buzzer sound off when the switch is triggered.
https://youtu.be/Qx2IbJRFGXM
But the light/buzzer didn't work after it was wired up in the nomad. (it DID work on the bench with 12 volts pushed thru it). Turns out the ECM signal output voltage for the fuel pump circuit is only about 5 volts, which is enough to trigger the fuel pump relay to shut off, but not enough to power up the light and buzzer. :eek: I'm gonna have to rethink this one and wire the light/buzzer to a full 12 volt source.

[55 Rescue Dog]

Pretty cool, and a good idea. You just need to run one more wire like you found out.

[chevynut]

How is “one more wire” going to solve the problem with only 3 terminals on the switch? I’d make sure the ECM is doing what you think it’s doing first. I would have expected the ECM to ground the relay coil. I’m pretty sure mine does.

[55 Rescue Dog]

True, just another wire won't do it. Since GM uses oil pressure as part of the fuel pump circuit it might be a little more involved, unless there is a 12 volt relay somewhere, sending power to the pump. The simplest way would be to just put the inertial switch in series directly to power the pump if it is capable of carrying the current of around 10 amps. That's the way Ford did it on a lot of vehicles, using the 3rd terminal to turn on a dash indicator light. It shouldn't see any duty cycle, which a relay would need to do every time you powered it up. I have had to troubleshoot many intermittent electrical problems that ended up being caused by a bad relay contact. Much easier with only a switch in the way. It was pretty easy to troubleshoot a relay on a machine tool back when you could check relay contacts by manually operating a relay by pushing it in with a screwdriver to check contact resistance. Too bad cars were not designed that way.

[chevynut]

I just got back from being gone for a few days and looked at my Holley C950 schematics. My ECM does supply power for the fuel pump relay. Apparently the LS ECM DOES supply power to the relay also, like other GM ECMs in earlier EFI engines. Here's an LS1 schematic.

http://chevythunder.com/1999x%20Fuel%20pump%20and%20fuel%20prress.%20senso r.gif

[chevynut]

What voltage is your buzzer designed to work on and how much current does it draw? The LED should easily light up if you have it wired right. Connect the "common" terminal of the inertia switch to the ECM output. Connect the NC terminal (the one that's shorted to common when the inertia switch is set) to the fuel pump relay coil. Connect the NO terminal to the buzzer and the light. The LED is polarity sensitive so you need to be sure it's wired correctly. I don't know about the buzzer. Note that the buzzer and light will ONLY be on when the ECM is trying to turn on the pump.

[chevynut]

Paul, which buzzer/LED are you using. Also, what is the brand and P/N of your fuel pump relay? I'd like to look at the specs. Those are usually 12V relays and I'm surprised it works at 5V on the coil.

You could always use another relay to turn on the power to the buzzer but it doesn't seem to me like you should need to.

[chevynut]

Here's some info.....you should see 12V on the ECM fuel pump control wire according to this:

https://ls1tech.com/forums/conversions-hybrids/1640749-ls1-pcm-fuel-pump-output-question.html

Also, a 12V relay should have at least 9V on the coil to operate correctly.

https://forum.digikey.com/t/understanding-relay-coil-voltage-specifications/946

[55 Rescue Dog]

It looks like the inertia switch should be in series with DK GRN/WHT wire 465 output from the PCM, and not the control input to the PCM? Assuming it's 12v going to the relay coil.

[WagonCrazy]

Here's how I wired it...
the light and buzzer now work when the switch is activated (thereby removing power to the fuel pump relay, which results in shutting off the engine).

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Link to the Inertia Switch https://www.ebay.com/itm/183727849647

Link to the LED light/buzzer https://www.amazon.com/gp/product/B07QN9XSQG/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&psc=1

[55 Rescue Dog]

Glad it works, but you should work on your schematic a little maybe. :)

[WagonCrazy]

i'm not an electrical engineer by any stretch. I'm a hack and trial and error guy with sometimes burnt fingers to show for it. :-D I'm expecing the full wrath from chevynut when he looks at my drawing and shitz...

[chevynut]

Paul, I'm not understanding your schematic. I can see how the fuel pump relay works. But I don't see how the buzzer can work with 12V on both sides of it. Where is the buzzer ground?

[WagonCrazy]

Laszlo.
So this is what Ive observed happening with this circuit.

the ECM puts out 12 volts when the key is first turned on. Then the engine starts and it continues putting 12 volts out thru the inertia switch and into the relay.

When I bump the switch (and it closes), the engine stalls within a second. When that happens, the ECM wire loses all voltage. Since it's connected to the C terminal on the switch, and the switch mechanically transfers the connection from the NC wire over to the NO wire...that NO wire now acts as a ground to the light/buzzer.

I first tried connecting the light/buzzer the "other way" (thinking the NO wire would now transfer the 12 volts coming from the ECM wire to the C wire within the switch, but since the engine dies that NO wire loses all voltage...so nothing powered up the light/buzzer with it connected in this manner).

So the NO wire becomes a ground when the engine dies, the ECM quits putting out 12volts, and that allows the light/buzzer to turn on (because of the 12 volt connection to battery power)

probably lost y'all on this by now. :mad:

[55 Rescue Dog]

I understand how you have it connected up now, but it's kind of a fluke the buzzer/light works that way. It must be finding a ground loop through the ECM which might not be good. I'm not really seeing a easy way to hook it up since the 12v goes away when the engine stops. I would think it would work briefly during the pump prime cycle when you first turn the key on when the inertia switch is tripped? The simple solution might be to just skip the light/buzzer and just put in a small indicator light to know when the fuel pump is on or off.

[chevynut]

I would have thought the ECM would "float" the fuel pump output instead of grounding it when it's not trying to turn the pump on. I don't know what kind of output driver they use in the ECM or how much current it can sink or source, but the buzzer probably only takes around 20mA to work. It's a piezoelectric buzzer and LED and neither take much current. I would guess the ECM has a FET output but it could be a relay. If it was a SPST relay it wouldn't work as wired. If it's a SPDT relay with ground on the NO terminal (inside the ECM), it would work fine. I wonder if there's a schematic for the internals of the ECM anywhere. It would be interesting to measure the resistance of the ECM fuel pump pin to ground with the power off.

The problem with your circuit is that if the ECM is trying to turn the pump on, but the inertia switch is tripped, the buzzer will NOT sound. And it looks like it would sound all the time with the key off and the inertia switch tripped, since the buzzer is always powered.

[chevynut]

Paul, if the ECM can power the relay with the 12V fuel pump output, it should be able to power the buzzer. Both require similar currents under 50mA. I'd check your wiring and try it again the first way. Wired that way, whenever the ECM is calling for the pump to turn on the buzzer will sound with the inertia switch tripped. That makes a lot more sense to me.

[55 Rescue Dog]

I believe the fuel pump output won't work with just key on, and the engine off, which you wouldn't want. I think the engine needs to be cranking, or running to fire up the pump.

[chevynut]

Paul, you might want to try this....I know it's possibly what you tried first, but it should work. Be sure to get the polarity on the buzzer/LED correct. Like I said, if the ECM can supply power to turn on the pump relay, it should be able to turn on the buzzer too.


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[55 Rescue Dog]

Paul, you might want to try this....I know it's possibly what you tried first, but it should work. Be sure to get the polarity on the buzzer/LED correct. Like I said, if the ECM can supply power to turn on the pump relay, it should be able to turn on the buzzer too.


10431
I think that's the way he had it hooked up the first time. The problem is the 12v goes away from the ECM when the engine shuts off. Good schematic though.

[chevynut]

I think that's the way he had it hooked up the first time. The problem is the 12v goes away from the ECM when the engine shuts off. Good schematic though.

It's not really a problem. If the inertia switch is tripped, the buzzer is connected to the ECM pump output. When the key is turned on, the pump output goes to 12V for 2 seconds before it shuts off. The buzzer will indicate a tripped inertia switch then. If you try cranking, the ECM will turn on the pump output, again sounding the buzzer.

The way he has it hooked up now it seems like the buzzer should be sounding all the time because the ECM isn't outputting 12V with the key off. The buzzer won't sound for the first two seconds after the key is turned on, until the ECM turns the output off. Then the buzzer won't sound while cranking.

I suspect Paul may have had something hooked up wrong the first time. It should work.

[55 Rescue Dog]

Yes is should work that way trying to start the engine, but that is the only time it will turn on the buzzer. And it won't work after the engine shuts off from the inertia switch is all. You would need to try and re-start the engine to see/hear that the switch had tripped out.

[WagonCrazy]

Some comments on your observations:

Chevynut-
It would be interesting to measure the resistance of the ECM fuel pump pin to ground with the power off. Yes, I plan to check that soon. I too would like to verify that there is some resistance in that "ground" circuit (when the engine is off...does that Pin09 really turn into a functional ground?)

RD-
I think that's the way he had it hooked up the first time. The problem is the 12v goes away from the ECM when the engine shuts off. Good schematic though. This is correct. So once that 12v signal goes away, there's no power to transfer (on the inertia switch) to the light//buzzer.

Chevynut-
It's not really a problem. If the inertia switch is tripped, the buzzer is connected to the ECM pump output. When the key is turned on, the pump output goes to 12V for 2 seconds before it shuts off. The buzzer will indicate a tripped inertia switch then. If you try cranking, the ECM will turn on the pump output, again sounding the buzzer.

The way he has it hooked up now it seems like the buzzer should be sounding all the time because the ECM isn't outputting 12V with the key off. The buzzer won't sound for the first two seconds after the key is turned on, until the ECM turns the output off. Then the buzzer won't sound while cranking. This is correct. But I have altered it since...and connected the 12v source to an "12v ignition on" connection point, rather than the "12v battery-always hot" connection point. This way it only sounds once it's been tripped, and stays sounding until i turn the key off.

RD-
Yes is should work that way trying to start the engine, but that is the only time it will turn on the buzzer. And it won't work after the engine shuts off from the inertia switch is all. You would need to try and re-start the engine to see/hear that the switch had tripped out. Correct. So this brings up a philosophical question about what we're trying to accomplish by including this inertia switch at all. I want a way for the pump to shut off in the event of a hard accident or rollover. In the event that I cannot physically turn the key "off", I want to know that the pump is shut off (because of the buzzer noise...that will confirm it). And that noise and light is a reminder that its shut off, should it "falsely shut off" for any reason. So technically, the ECU stops giving the signal when the engine dies (for any reason), so in an accident or rollover when the engine dies...the pump quits pumping fuel because the ECU signal is not there. And that's fine. But if the accident isn't bad enough to stall the car, and it keeps running, and I'm incapacitated, it want that pump to shut off. Seen too many people burn up in vehicles where they are incapacitated, and it appears fuel is just constantly running out fanning flames.

So for now, this is working as designed. But I will check that question about ground resistance back to the ECU Laslzo... because I'd like to know what's happening. Mabye I'll shoot and post a short video when I do that..

[chevynut]

Paul, I think connecting the buzzer to switched power makes more sense and the benefit is that as soon as you turn on the key it tells you the switch is tripped. Probably not a bad way to do it if the ECM really does hound the output when not outputting 12v. I’ll have to check mine to see if it works that way too.

[WagonCrazy]

Update:
All of this back and forth on "ECU grounding" that makes the light/buzzer work when tripped" has been haunting me.
So I went back thru it and confirmed a few things:

1. Laszlo's schematic is CORRECT. This is how I have it wired...
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2. I changed the electrical source from 12v Battery (always on) to 12v Switched (which only works with the key in the on position). Once I turn the key to OFF, the light/buzzer goes dead. (as I originally wanted).

2. The polarity (wire connection points) on the LED light/buzzer DOES matter...I had it wired backwards the first time thru and couldn't get it to work (once the inertia switch was tripped).

3. ECU Pin 09/Red CONTINUES to put out 12 volts AFTER the engine has stopped (either due to the inertia switch tripping OR just due to the engine dying and not running). It does NOT "go to ground once the engine dies" as I had stated in an earlier post. Disregard all mention of that please...

4. When the inertia switch is tripped, it transfers the 12 volts AWAY FROM the fuel pump relay and INTO the LED light/buzzer, and makes noise (as long as the key is still in the on position). The fuel pump stops running immediately, and the engine dies within 2 seconds of the pump no longer running.

Sorry for all the confusion on this.

[WagonCrazy]

And these are the items I used:

Inertia Switch: $10 and no shipping. Ebay- https://www.ebay.com/itm/183727849647
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There is no "3rd wire" in that harness plug, so you'll have to make one and install it yourself.

LED Light/Buzzer: $6 and no shipping. Amazon prime https://www.amazon.com/gp/product/B07QN9XSQG/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&psc=1
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