1 Topic by gunn (edited by gunn 2011-03-03 04:54 PM)

  • gunn
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Topic: Q: Do I need an inertial fuel pump cutoff switch? Should I bypass it?

My rookie team and I had a work day this past weekend and after one of my fellow monkeys... team members found the inertial fuel pump shutoff switch and he proceeded to turn it off. 20 minutes of trying to figure out what the hell I had done to the ECU/dash/gauge cluster (I was mucking around in the front at the time) later, it finally dawned on me what had happened.

Anyways, I started thinking about the possibility of being bumped (or bumping into somebody) on the track and it occured to me that should the inertial switch get tripped, it's going to be super inconvenient (and quite possibly dangerous) to go all the way back into the trunk to push the switch down again.

My thought is that perhaps I should wire in a bypass (either to eliminate it altogether or to bring the cutoff switch forwards to the driver's dash area). Plus, this also gives me another item I can sell to the enthusiasts on TCCOA.com

I understand it's meant to cut off the fuel pump in the event of an accident but without power (i.e.: with the kill switch turned to OFF), the same result will occur.

Q: Is eliminating this inertial switch a good idea?
Q: If so, should I just go ahead and deactivate it completely (short it out) or should I run a wire so that I have manual cutoff capabilities from the driver's console?

I know this may seem like a mundane question to you folks rebuilding 50's radial engines to shoehorn into small cars but this is the first project car we've taken on and we want to do things right. Or attempt to at least.

Thanks in advance for your replies,
-g

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  • From: Newton, KS
  • Registered: 2010-02-23
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Re: Q: Do I need an inertial fuel pump cutoff switch? Should I bypass it?

Bypass and remove the switch. I know the rules do not require it, but it is never a bad idea to have a battery cut-off switch that the driver can reach (whether or not this requires a second switch to do so) just in case there is a need to cut power for items such as the fuel pump.

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  • DaveH
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Re: Q: Do I need an inertial fuel pump cutoff switch? Should I bypass it?

Yup, get rid of it.  The last thing you want is to get rear-ended and have the motor die in the middle of the track.  Run a dedicated switch for the fuel pump within reach of the driver.  Make sure you feed it from the kill switch, not directly from the battery.  Both this switch and the safety kill switch should kill the fuel pump.

The other plus of this method is that you can test with the fuel pump on and the ignition off or vice versa.  It can come in handy diagnosing problems.

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  • From: Da Nati, oh
  • Registered: 2009-10-07
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Re: Q: Do I need an inertial fuel pump cutoff switch? Should I bypass it?

We started with a 98 crown vic interceptor (currently unofficially for sale)and to our surprise for being an interceptor we had the idea that a police (or in our case a City parks car) that this wasn't deleted for police duty.

Anyways... back on track

Our first race at CMP it tripped without reason. It tripped again at another race but I believe it was due to an accident. I said the heck with it and unplugged and removed the button from the trunk. I then jammed a wire in the connector and zip-tied the wire in place. We haven't had a problem since, till my brother picked up a car we been racing lately. now the battered beauty is just sitting in storage burning a hole in our pockets.

so to answer your question... Yes get rid of that mo-fracker. It's trouble waiting to give you trouble on race day.

5 Reply by Sledge (edited by Sledge 2011-03-03 08:43 PM)

  • Sledge
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Re: Q: Do I need an inertial fuel pump cutoff switch? Should I bypass it?

We have one as well in the trunk of the t-bird.  Didn't have any problems with it at our first race, but I am going to bypass it for the second.  I recommend you do the same.

As for a cutoff switch, our ford had a 60 amp fuse in the engine bay power distribution box that controlled both ignition circuits (we have 2 coil packs).  We simply ran a line from both sides of where the fuse hooked up to the cutoff switch, with the fuse wired inline.  We put the cutoff switch inside the drivers door so that it both the driver and anyone outside the vehicle can reach it.

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  • From: Land Of Subarus, Colorado
  • Registered: 2009-04-30
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Re: Q: Do I need an inertial fuel pump cutoff switch? Should I bypass it?

I recommend an oil-pressure-actuated fuel pump switch, the kind with a separate circuit to energize the pump when the starter is cranking.

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7 Reply by TeamDFL (edited by TeamDFL 2011-03-04 05:43 AM)

  • From: Craphole, NJ
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Re: Q: Do I need an inertial fuel pump cutoff switch? Should I bypass it?

Judge Phil wrote:

I recommend an oil-pressure-actuated fuel pump switch, the kind with a separate circuit to energize the pump when the starter is cranking.

If you lost fuel when oil pressure goes away, how are you going to drive 3 laps and throw a rod into the paddock?

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  • jrbe
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Re: Q: Do I need an inertial fuel pump cutoff switch? Should I bypass it?

If you wire up a fuel pump switch in its place it becomes a fuel pump kill switch.  You can just bypass it (connect the 2 wires) and let the ecu control the fuel pump as recommended.

I would stay away from a fuel pump switch that runs the pump key on.  If you get knocked out and the fuel is leaking the last thing you want is the fuel pump still running or having to remember to shut the switch off.  Basically leaving the ecu in control of it is the safest way.

  Oil pressure is good too but if your engine gets oil starved in a corner you end up fuel starved too unless there is a delay circuit built in.

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  • Serj
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Re: Q: Do I need an inertial fuel pump cutoff switch? Should I bypass it?

jrbe wrote:

If you wire up a fuel pump switch in its place it becomes a fuel pump kill switch.  You can just bypass it (connect the 2 wires) and let the ecu control the fuel pump as recommended.

I would stay away from a fuel pump switch that runs the pump key on.  If you get knocked out and the fuel is leaking the last thing you want is the fuel pump still running or having to remember to shut the switch off.  Basically leaving the ecu in control of it is the safest way.

  Oil pressure is good too but if your engine gets oil starved in a corner you end up fuel starved too unless there is a delay circuit built in.

throw a small capacitor inline to the fuelpump wiring so it'll run for another few seconds before cut-off? you probably wouldn't want to do this in anything other than the oil pressure scenario though.

  • Mulry
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Re: Q: Do I need an inertial fuel pump cutoff switch? Should I bypass it?

My suggestion: run your fuel pump switch through a relay. Wire the relay to ignition/key power, so that you can't have the fuel pump on unless you have the ign switch on (that way you kill the fuel pump when you kill the ign). Car doesn't have to be running, just ign on.

In other words, take a wire from the hot side of the ignition to the bottom terminal on the fuel pump cutoff switch, then the other side of that to the appropriate terminal on the relay. Then wire the relay per the normal instructions. That way you're not running full voltage through switchgear that might not be able to handle it and you've got it controlled both by the fuel pump switch and by the ign switch. Just my  2 cents. But Bosch-style 4-post relays are cheap cheap cheap on eBay thanks to global commerce. smile

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  • DaveH
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Re: Q: Do I need an inertial fuel pump cutoff switch? Should I bypass it?

hrlyTCH wrote:

We started with a 98 crown vic interceptor (currently unofficially for sale)and to our surprise for being an interceptor we had the idea that a police (or in our case a City parks car) that this wasn't deleted for police duty.

Yup, ran into one on our CVPI as well, and it actually was a NY cop car (either county or townie).  Hint: if the cops are chasing you, hit them in the driver's rear quarterpanel.

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  • gunn
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Re: Q: Do I need an inertial fuel pump cutoff switch? Should I bypass it?

jrbe wrote:

If you wire up a fuel pump switch in its place it becomes a fuel pump kill switch.  You can just bypass it (connect the 2 wires) and let the ecu control the fuel pump as recommended.

I would stay away from a fuel pump switch that runs the pump key on.  If you get knocked out and the fuel is leaking the last thing you want is the fuel pump still running or having to remember to shut the switch off.  Basically leaving the ecu in control of it is the safest way.

  Oil pressure is good too but if your engine gets oil starved in a corner you end up fuel starved too unless there is a delay circuit built in.

That's my gameplan. I plan to override the inertial switch, not the ECU.
I'll put it on the rapidly growing list of "stuff to be stuck on the new dash console."

-g

So far I have:
* Coolant Temp Gauge
* Oil Pressure Gauge
* ATF Temp Gauge (automatic tranny so this is a concern)
* Fan motor override (so I can run at full speed while the car is off)
* Fuel pump cutoff (cuts out just like the inertial sensor)
* rear defroster (why not, it's already there and I took out the center console it was mounted to)
* Trunk release button  (ditto above)
* Gas door release button (ditto above)
....
More to come I'm sure (like the comm system and the dangerous homemade tech bits)

Myopic Motorsport's #888 Ceci n'est pas une Citron Thunderbird ("This is not a lemon" but a 1995 tbird w/ 93 V8 swap + shopping cart rear wing + engine mounted frito maker)
2017 Sears Pointless Organizer’s Choice
Frito Making Tbird from 2018 Sears Pointless Engine Heat BBQ - http://goo.gl/csaet4