Fuel pump on/off dash toggle switch - where in the circuit?

[beeman]

I'm just wondering if I should wire the dashboard fuel pump toggle switch (basically an override shutoff) before the relay or afterwards. I'd prefer to have it between the PCM and the relay to keep the amperage lower through the switch, but is there ever a situation where the relay could get stuck in the activated position? If so, I should probably have the switch wired between the relay and the pump motor to have complete control over the pump.
Thoughts?

[Papa]

I'd wire it on the ground side of the relay, similar to how an inertia switch works. That way, the switch isn't carrying any current.

[Bob Cowan]

I'd wire it on the ground side of the relay, similar to how an inertia switch works. That way, the switch isn't carrying any current.

That's what I would do.

[VRaptor SpeedWorks, LLC]

Ditto.....I would run the ground wire from the ECU to the toggle and then to the ground side of the relay. If you used the toggle to interrupt the power circuit, you'd be running heavy gauge wire from the engine fuse box, all the way up front to the toggle, then all the way back to the pump. I'd worry a lot more about ending up with voltage drop to the pump due to 20' of wiring and thru a toggle switch before I'd worry about stuck relay contacts.

[beeman]

Perfect, thanks guys! Now why didn't I think about that....

[jamesfr58]

I have one that is wired to the ground side of the relay, can trip pump on and off in cab, my relay and all wiring and right next to the pump power supplied from stand alone ECU and power distribution supplied with the create motor.

[beeman]

Just to confirm... The dg/wht wire from the PCM that goes to the pump relay is a 12V +. Looks that way in the wiring diagram.

[crash]

I'm speaking about an LS3 here, but you do understand that it has a deadhead rail system, right? Basically the only way the fuel pressure is regulated at the injectors is via pump control via ECU. If you override this you can cause some problems. Why the desire to put this override into the system?

[beeman]

Mainly to minimize the size of the fire.
I also have an inertia switch wired, now to the relay ground, in line with the toggle switch. Yes, LS3 with LS1 C5 PCM.

You make a good point though, I'm not installing the switch for any 'cool factor', it will always be in the on position unless I need the fuel off asap. I don't want to piss of the PCM.

[beeman]

I had discussed this in my build thread a while back. Correct me if I am wrong, I'm unoffendable!

There is no inertia cutoff. The PCM does control the fuel pump and apparently will eventually kill power to the fuel pump if the engine dies. That's potentially more spraying fuel than I want.

If a fuel line is compromised, the fuel rail will see a pressure drop which I'm guessing will tell the pump to send more fuel?

[jamesfr58]

I have modified fuel rails on my LS3 not the dead head one that come on create engine. The fuel is held a 58 psi by a regulator after the fuel rails with fuel allowed through the regulator back into passengers side tank. I put a fuel cutoff switch in cab to as Beeman said minimize fire risk by insuring I can cut power to the fuel pump.

[VRaptor SpeedWorks, LLC]

Ohhh....yeah, it appears that is correct!...which means our advice is bad. I'm so used to wiring up crate engines that I take for granted that the ECU controls the ground to the relay trigger and not the power to it. You are correct...the relay is hard-grounded to the chassis and the ECU controls the power to it.....so you would want to interrupt that DK-GR/W wire with your toggle switch or the ground side of the FP relay. Probably safer to interupt the ground circuit of the relay trigger.....somewhere between the relay and "splice pack 122" on your schematic.

[beeman]

Thanks again guys, sorry I didn't clarify my system initially.

[crash]

Okay, got it. For some reason I thought you were using it to prime the system or something. Our fuel pressure sender is actually pretty far away from the rail so not sure something like a crushed rail would have much of an effect, but then I can't remember where the sensor is on a "stock" setup? I can tell you that a fuel pump, even when turned off, that is controlled by the ECU can end up pumping fuel during a fire. Our best guess is that the ground wire melted enough to short to the frame and then the pump came on. Unfortunately neither the driver nor the safety crew turned the correct master switch off to cut power to the entire car. This caused the PDG car to burn for quite some time a couple years back. You can hear in the video where the pump goes off with the ignition switch, then, as the fire burns, but gets smaller, the pump kicks back on and the fire accelerates quickly. Both driver and safety crew attempted to turn the master off, but they actually turned the battery selector switch which is right under the master cut switch.

[KGTM]

Crazy question, why having a pump off switch? in what case would one use it?

Mostafa

[beeman]

I can tell you that a fuel pump, even when turned off, that is controlled by the ECU can end up pumping fuel during a fire.

That's a valid point, Mike, losing the insulation on a ground-activated relay wire will kick the relay back on as soon as it contacts the frame. The only fool proof way to kill the fuel pump is to cut power to the fuel pump relay. So I'll have a red-capped fuel pump toggle switch very close to the shifter to slap down in a quarter of a second, but I can't forget to reach for the battery disconnect (mine's on the driver's side of the tunnel) before exiting the car. I'm leaning towards a fire suppression system as well.

[KGTM]

I guess I still do not understand, why not turn the ECU off ( ignition)? that re removed 12V and shut off other stuff also.

I do understand the thought of having fuel shut off but I am really trying to understand what you are trying to avoid that ECO off will not do?

I have placed fuel pump inertia switch to cut the fuel pump off, it is not directly connected to any fuel pump, just tell my system to turn fuel pump off, I can soft reset it from dash just in case it went off with a bad bump and reset when I stop.

Mostafa

[beeman]

In my setup, the ignition key is only used for the starter. Everything electrical is activated by the battery cutoff switch via fuse blocks except for the always on ECU circuits.

[KGTM]

In crate engine, there is only one 12v for ECU connection and Pink wire ( ignition) to activate it, once that happens pump comes on and other circuit are activated, and removed that it all turned off, it yours different?

I am certainly not car builder like some of you guys and really just trying to understand the need so if it really save me I can Add one also, but does not want to add if odds of helping me is not much when I need it the most.

Crash, you race a lot, Has your ECO ever gone BAD and left the pump on while in the middle of accident after turning the ECU off or what ever you have to turn it off?

[beeman]

Even with the crate engine, I'd highly recommend you install an inertia switch. I cannot find anything that suggests GM used one on the C5 or crate motors. The Ford one is nice and cheap, I put one in my Roadster and now the GTM. If you are tracking it, note that the switch can trigger with extreme driving, in that case install it where you can reach it belted in. And buy one that has the pigtail included.

https://rover.ebay.com/rover/0/0/0?m...Fp%2F679741233

[KGTM]

I do have one if this https://www.pegasusautoracing.com/pr...SABEgL4r_D_BwE already.

it is not directly connected to pump, just lets my system know to turn pump off, I just need to program it, I can also bypass it if accidentally goes off if I want too.

Mostafa

[Papa]

I do have one if this https://www.pegasusautoracing.com/pr...SABEgL4r_D_BwE already.

it is not directly connected to pump, just lets my system know to turn pump off, I just need to program it, I can also bypass it if accidentally goes off if I want too.

Mostafa

That is an inertia switch. There is a ball that gets held in a cage when you depress the plunger. With a significant enough jolt or impact, the ball pops out of the cage and that interrupts the circuit that the switch is wired into (typically the ground wire for the fuel pump relay or pump). This is the same switch that comes with the roadster kits.

[Shoeless]

I'm wondering about mounting these inertia switches near the driver only cutting power or ground to the relay controlling the fuel pump with the situation that Crash mentioned. If there is a fire and a wire melts in the circuit allowing it to ground out after the switch, then the switch did noting to help you.

I plan on putting one of these inertia switches on the 12v wire going to the fuel pump as close to the fuel pump as I can. If memory serves me, most GM fuel pumps draw about 8 amps, so the one Mostafa share is perfect.

If it trips, than it did for a reason (high impact). I couldn't imagine any regular driving forces that would trigger this accidentally where you would want to immediately reset it without investigating. Am I missing something here?

[beeman]

I've had the Ford switch trigger on high g cornering in the Roadster on 2 different tracks. The first time I thought I lost the engine so I was happy to realize what had happened. Both episodes required me explaining to a corner worker how to reset it in the trunk (they don't like you leaving the car unless it's on fire). Now it's within reach.

[Shoeless]

I've had the Ford switch trigger on high g cornering in the Roadster on 2 different tracks. The first time I thought I lost the engine so I was happy to realize what had happened. Both episodes required me explaining to a corner worker how to reset it in the trunk (they don't like you leaving the car unless it's on fire). Now it's within reach.

That makes sense now. How do you have it wired up in your roadster?

[beeman]

Just like it was wired in the 04 Mustang Mach 1 donor, near the fuel tank, I'm pretty sure between the relay and the pump motor.

[Shoeless]

I guess it wouldn’t hurt to run a power wire up to the dash area to this switch then back to the fuel pump. I’m trying to keep my engine wiring harness and power distribution separate from the chassis wiring harness and connected with one Deutsch AS connector. I’ll have to review a higher current option for a different plug.

[beeman]

For the GTM, I'm going to run both the kill toggle and the inertia switch to the relay ground as recommended above.

[Shoeless]

I just referenced back to my schematic for my wiring diagram and happen to have two 20 ga pin openings in my body connect Deutsch AS plug. That would be perfect to use the relay ground circuit to trip this with the inertia switch.

Thanks for the dialogue on this.

[beeman]

And all bets are off if there is still voltage when things start melting so have access to the battery cutoff.

[KGTM]

personally in case of fire, I will just get out of the car fast and whatever happens will happen.

I have two pump in my car, one draws about 9.8 amp or so the other 12.5 amp, since it is different model but for same model C5 2004, so personally I would NOT connect in line with pump, you will drop also going voltage back and forth.

20200112_162753.jpg

Above is Where I have mine about center front. above battery area, Hope It will never need it.

Mostafa

[crash]

Crash, you race a lot, Has your ECO ever gone BAD and left the pump on while in the middle of accident after turning the ECU off or what ever you have to turn it off?

Only the one that happened and I mentioned with the fire. I have had only one other major incident and that was a guy that drilled me from the side. I think the G meter peaked during that event. 10G? 7G? can't remember, but it was significant and probably a bit more than the G meter recorded. Took out a lot of things, but the engine kept running and no major leaks from oil/water/fuel.

[Bob Cowan]

We're making this way more complicate than it needs to be. If the ECU controls the fuel pump, then it will shut off when there are no RPM's detected. That will happen much faster than you can do it yourself.

If you're racing, you should have a master cut off switch for the battery. Engine quits, hit the switch, everything stops. Simple and easy.

The inertia switch should really only be used on a street car. And even then, used with caution in these cars. As said above, hard cornering can trip the switch at the worst possible moment. Then bad things can happen. Same thing can happen on the street. I originally installed one in mine. But during hard launches or donuts, it would trip. very annoying. I took it out.

IMO, there's no need for any additional controls. Let the ECU do it's thing and don't worry about it.

[beeman]

I don't disagree with you, Bob. For a track only car, I wouldn't install the inertia switch. I even over-rode the switch at M1 Concourse/Champion Raceway when it triggered unnecessarily (which it has never done on the road, nor would I expect it to). I'm not sure where it would be dangerous though, just very annoying. The car just began losing power, sputtered, stopped, and would not restart.

That being said, the inertia switch does some work for you when you can't- i.e. you are knocked cold and the car is still running. On the track with a helmet and harness, this is less likely. Plus you have a corner worker with a fire extinguisher within 100m or so.

[Bob Cowan]

I'm not sure where it would be dangerous though, just very annoying. The car just began losing power, sputtered, stopped, and would not restart.
.

When you're in traffic in the middle of the chicane, and suddenly you lose power. :0

[KGTM]

You guys are way too pro for me, Had to look up the meaning of chicane, you do not want to be in the middle of that with no power.

I am going to make it so I can disable the inertia switch by my touch screen, right now it is just there, I will do code for it later.

Lively discussion all.

Mostafa