I have an S14. I was wondering if anyone has had any experience with a fuel cut-off switch. If anyone can help me out please PM me. Thanks!
Ryan.
you want to get rid of the factory one speed limter or you want to make one?
I want to make one so that I can turn off the fuel pump with a switch
find the fuel pump wire, it’s black w/ pink stripe IIRC, just cut it and put a switch in series with it.
ie. ECU — pretty wire ----> switch -----> fuel pump relay
I’d check ecu pin outs online first before you start cutting into junk.
is better to have a relay on it rahter then just have a switch on it…
the current on the fuel pump wire might burnt the switch
doesnt the fuel pump go and off and not always just on, if you force it to always on presume wouldnt be the best idea, if your gonnar removed your speed limiter, do it right with a controller
Zeta_g,
that wire just primes the coil for the fuel pump relay. I guess you could include a relay but adding a relay to trigger another relay seems kinda overkill.
and asserfate,
I would think that the fuel pump is always on, and a fuel cut doesn’t stop the pump it just stops the injectors.
shutting off the pump takes time, first, the relay has to respond, and then the pressure needs to drop, this can take a second or two. then the pump would have to turn on again (relay takes time) and the system would have to pressurize all over again. seems like a bad design since you would run lean while the pump primes/unprimes/primes/unprimes, and also the rev limiter would be bouncing over a huge rpm range.
when you’re bouncing over the rev limiter a few seconds is the difference between blowing the motor up and not. and I would also think that the speed limiter uses the same fuel cut mechanism.
I’m only assuming but it makes sense to me.
oooh
cuz while i wired up my alarm system
i had the cut off relay inline w/ the fuel pump 12v supply
and i donno theres an other wire u can just hook up a switch to…
put the key to on position, dont start your car, and listen to your fuel pump, after about 7 seconds it will stop, you can easily hear it when its a walbro, its not proportional speed but it is controled by the ecu in terms of on/off.
there is no way the ecu turns the pump on /off to control the amount of fuel, it controls the injectors, the pump is always on,
the ecu is never in direct control of the pump, it goes it through a relay.
and for poeple that do the hardwire mod sometimes even two… and those people still have rev limit / speed limits.
Well, the ECU has some control over the switch… there is a fuel pump relay wire going to the ECU
Well, the ECU has some control over the switch… there is a fuel pump relay wire going to the ECU[/quote]
don the ECU just turns on the fuel pump when ever the key is turned on?
and the fuel pump should be always on
that’s why I said it’s never in direct control 
I actually have two relays, when I got my walbro I did the hardwire mod and I was too lazy to eliminate the orginal relay circuit so I have:
ECU primes old pump relay, old pump relay primes hardwired relay, hardwired relay connects pump directly to the battery.
it’s insanely loud at 12V, people ask me what that f’in’ hummmmm is all the time. once you start driving though the road noise covers it up.
what your hearing is the pump building pressure , once it’s at pressure then the pump no longer needs to work as hard and it simply contineus to turn over pushing a stable fuel rate and the pressure set by the FPR.
the only time you will ever get a fuel pump that turns on/off in relation to pressure is in a returnless fuel system. ( no return fuel line) , the focus is an example of this.
[quote=“alesserfate”]
put the key to on position, dont start your car, and listen to your fuel pump, after about 7 seconds it will stop, you can easily hear it when its a walbro, its not proportional speed but it is controled by the ecu in terms of on/off.[/quote]
The fuel pump turns on and off based on weather or not the flywheel is turning. If the flywheel isn’t moving ie when you move the key to ACC the pump primes for 3 seconds and then stops if the flywheel doesn’t start moving. Once you start the car the pump is always on until the flywheel stops moving then it cuts the fuel pump.
If that makes sense.
the pump doesn’t turn on when ACC(essories) does… if that was the case then you’d run out of battery so fast when trying ot listen to the radio or somethiing. it’s when your IGN goes on.
and it doesn’t stop after three seconds… if you have an FPR/fuel pressure guage you’d see that once the ignition is on the pump stays on, regardless if the motor is going or not.
it’s louder for that initial bit because there is no pressure so it’s free to move with less resistance… it’s kinda like when you press a grinder/dremel/chainsaw into whatever you’re cutting… once you start applying pressure the tone completely changes / slows done considerably.
I did it…just take the ground wire off of the pump and splice a wire to wherever you need the switch…
the pump doesn’t turn on when ACC(essories) does… if that was the case then you’d run out of battery so fast when trying ot listen to the radio or somethiing. it’s when your IGN goes on.
and it doesn’t stop after three seconds… if you have an FPR/fuel pressure guage you’d see that once the ignition is on the pump stays on, regardless if the motor is going or not.
it’s louder for that initial bit because there is no pressure so it’s free to move with less resistance… it’s kinda like when you press a grinder/dremel/chainsaw into whatever you’re cutting… once you start applying pressure the tone completely changes / slows done considerably.[/quote]
luka,
I think you might be confused by your fuel pressure gauge. The gauge still shows pressure even after the car is off - does that mean the pump is still going after you shut the car off?
when you turn your key to ACC the fuel pump turns on for X seconds (3 if hurricane is accurate, I’m not sure how many seconds myself) to pressurize the fuel rail. It does not start again until you start turning over the motor (ie; flywheel spinning like hurricane said).
If your car was gutted like mine was, you would know exactly when the fuel pump is on and when it is off - you can hear it very clearly 
Jammin is right.
except it’s the ON position not ACC.
but yeah, same shite
the pump doesn’t turn on when ACC(essories) does… if that was the case then you’d run out of battery so fast when trying ot listen to the radio or somethiing. it’s when your IGN goes on.
and it doesn’t stop after three seconds… if you have an FPR/fuel pressure guage you’d see that once the ignition is on the pump stays on, regardless if the motor is going or not.
it’s louder for that initial bit because there is no pressure so it’s free to move with less resistance… it’s kinda like when you press a grinder/dremel/chainsaw into whatever you’re cutting… once you start applying pressure the tone completely changes / slows done considerably.[/quote]
luka,
I think you might be confused by your fuel pressure gauge. The gauge still shows pressure even after the car is off - does that mean the pump is still going after you shut the car off?
when you turn your key to ACC the fuel pump turns on for X seconds (3 if hurricane is accurate, I’m not sure how many seconds myself) to pressurize the fuel rail. It does not start again until you start turning over the motor (ie; flywheel spinning like hurricane said).
If your car was gutted like mine was, you would know exactly when the fuel pump is on and when it is off - you can hear it very clearly :)[/quote]
when you turn the key to ‘on’ position the pump runs for x number of seconds and shuts off, the reason you see pressure on the gauge is because it has built that pressure, if you get your friend to start the car after that, you will hear it come on if you stick your head right by it, when you dont hear the walbro, means its off, ecu has control in terms of on and off, i doubt that it ever shuts off while the engine is running, but when the engine is NOT running and key is in ON its probably on a timer…