Fuel Pump Switch Wiring Questions

[turbosax2]

Lately my brother (snowborder714) and I have been piecing together a complete fuel system for his 95 GST (including lines, pumps, afpr, injectors etc.) to be installed in the somewhat near future. I am posting this instead of him because these are mostly my ideas. We're considering going with a Walbro 255 intank pump, which he already has and it is rewired, and a Walbro 255 inline pump. We have read on numerous posts that that Aermotive afpr's do not hold the fuel pressure and will drop to zero in roughly a few hours. People complain that if they let their car sit for a few hours then try to start it, it takes a few more cranks than usual to get it started. To alleviate that problem, some people have suggested installing a switch for the fuel pump. Now, on to my questions for all of you.

We want one switch that will turn on both of the fuel pumps - the catch is:
The switch should not be able to turn the pumps on if the key is in the off position or not in ignition switch.
The switch should not be able to turn the pumps off when the car is running.
The switch should only be able to turn the pumps on or off when the key is in the accessory position.

With that being said, the normal procedure for starting the car would be as follows:
Put key to accessory position, turn switch on to activate pumps and build fuel pressure, start car, turn switch off but pumps continue to run.

We need to know how to wire the switch so that it meets those requirements. Also, we need to know how to wire up the external pump.

I made a crappy drawing on Paint of the only way I could think to do it, but I don't think this way would work. (Ignore the wrong orientation of terminals on relay.) Neither my brother nor I are wiring experts but we understand some of the basics and have done simple wiring on gauges and lights.

Please, do NOT turn this thread into a discussion on need of external pump or need of the switch. I am just interested in how to wire them correctly in case we do decide to go with an external pump and/or switch for the pumps.

Thanks everybody for your help in advance!

 

[steve]

I think your trying way too hard to solve a problem that is due to either a leaking fitting between the pump and fuel line in the tank or a bad regulator. There isn't any reason why a properly working 255 lph pump and regulator can't build presssure as soon as you turn it on.

What setup are you going to run that you need both a intank and inline 255?

Steve

 

[snowborder714]

Steve,

I am building up my car so in the future when I upgrade my engine and turbo, the fuel system can handle it. I don't have any problems with the current setup. Sorry for any confusion, but the only fuel system upgrade I have is a Walbro 255 in tank.

My current fuel system will need an AFPR seeing as I am running an in tank 255. But I am just going to upgrade the whole fuel system so that it can support anything I want to throw at it (yes, it's overkill now, but will be put to good use later). With the AFPR, it slowly bleeds off the fuel pressure. So, if my car sits for longer than a few hours, the fuel pressure won't be there and will take a few extra cranks to build it back up. To avoid cranking it, I want to be able to turn on fuel pumps before starting car so that it will build up the fuel pressure and I can crank it right up.

 

[Defiant]

As far as switching that relay is concerned, just put your switch between 85 and the ground.

 

[compression]

That is what i did, exept i can turn the fuel pump on/off whenever . i think its fine like that. i just ran the ground from 85-switch-ground.

 

[turbosax2]

I do not want to be able to turn the pump on or off whenever. Basically, I want the pump to be off if the engine dies for safety reasons. If I put the switch on the grounding wire, would that work the way I want it to?

 

[snowborder714]

Also, how would that work for switching on fuel pump if car is off? When you flip that switch, it wouldn't necessarily turn the fuel pump on without having to start the car, would it? I would think that if I put it in the ground wire, that if I switched it off while the car was on, the fuel pump would then shut off because it doesn't have a ground.

I may also be looking at this completely wrong as I just woke up.

 

[compression]

your right, i had my fuel pump hardwired at one point and i changed it back. i just eliminated 86 pretty much , i put my switch in between 86 and a 12v source. if im not mistaken you can take 86 which is the wire that tells the fuel pump the ignition switch is on, and run that to a switch and from the switch to the fuse box to a fuse that is only hot when in the ignition position.

unless im completely misunderstood im having a major brainfart.. and my gf is driving my car so i cant go look at it really quick.

 

[compression]

Also, how would that work for switching on fuel pump if car is off? When you flip that switch, it wouldn't necessarily turn the fuel pump on without having to start the car, would it? I would think that if I put it in the ground wire, that if I switched it off while the car was on, the fuel pump would then shut off because it doesn't have a ground.

I may also be looking at this completely wrong as I just woke up.

the fuel pump would shut off because it wont have a ground correct. but whats wrong with that? it wont shut off unless you want it to and flip the switch. either way you look at it if the car dies and the key is still in the ignition position and the switch is on then the fuel pump will stay on. so how is the fuel pump supposed to shut off when the car dies?

 

[eclipsh]

turbosax2 PMed me about my tech article and asked that I post here about it.

My wiring system does not shut the pump off with the engine either. If the key is in the "ON" position, the pumps are running unless you turn off the ground switch on the relay. As stated in the article, there may be a wire from the ECU that would work better than the heater relay, I just haven't gone looking for it. With the setup I used any wire that goes hot when the key is in the "ON" position works just fine.

I'd be very happy to hear of a wire that does work better, and will add it to the tech article with credit to the one who finds it

It would be very easy to modify the setup to have a second switch in between the heater relay and pump relay if desired. I'd rather find a good wire that goes hot on the ECU coming on and dies with the engine. The logging wire should do that actually, and it is right nearby but I don't know how the voltage acts.

 

[turbosax2]

turbosax2 PMed me about my tech article and asked that I post here about it.

My wiring system does not shut the pump off with the engine either. If the key is in the "ON" position, the pumps are running unless you turn off the ground switch on the relay. As stated in the article, there may be a wire from the ECU that would work better than the heater relay, I just haven't gone looking for it. With the setup I used any wire that goes hot when the key is in the "ON" position works just fine.

I'd be very happy to hear of a wire that does work better, and will add it to the tech article with credit to the one who finds it

So we're looking for a wire that is live when the key is at the "on" position and the "start" position (only used while the car is cranking over), but will lose power if the engine dies?

 

[eclipsh]

Yup.

Alternatively, a two wire system could still be used if that additional wire loses power in the "Start" position (like so many do) but it needs to lose power when the engine dies.

A diode could also be wired into this line so power only goes one way, no feedback.

 

[turbosax2]

Yup.

Alternatively, a two wire system could still be used if that additional wire loses power in the "Start" position (like so many do) but it needs to lose power when the engine dies.

A diode could also be wired into this line so power only goes one way, no feedback.

Where would the diode be placed and what would that accomplish by eliminating feedback? I'm simply not familiar with diodes.

 

[turbosax2]

So we're looking for a wire that is live when the key is at the "on" position and the "start" position (only used while the car is cranking over), but will lose power if the engine dies?

Well, I found some good wiring diagrams. Anybody have any ideas on which wire(s) might work without going through and checking all of them?

http://www.vfaq.com/mods/wiring-gen2wir.html
http://www.vfaq.com/mods/ecu-harness-2G.html

 

[eclipsh]

A diode only allows power to flow in one direction. Putting one or two in line would prevent power from feeding back and forth across the system so it was only powering the relay. Feedback might have been the wrong term.

Pins 12, 13 and 25 might be worth checking out.

 

[turbosax2]

Should I use a diode if I find 1 wire to power the relay, or is that only if i go with the 2 wire system?

 

[eclipsh]

Only for the two wire setup.

 

[turbosax2]

And would the diode go on the old fuel pump wire or the heater wire? Also, what type/size of diode should be used?

 

[SFRacingGST]

Not for nothing, but why don't you locate the problem (fixing why your fuel system is loosing pressure) rather than putting a band aid on it? Seems like a waste of effort and time to go about wiring the whole fuel system off a switch rather than running it the way it was meant to. I am not sure if i am over looking anything, but if you fix your FPR or what ever is cause the leak than your should be golden . Also wouldn't a leak, even if it is small cause a loss of presure while driving also??
Just my 2 sense, good luck

 

[steve]

Not for nothing, but why don't you locate the problem (fixing why your fuel system is loosing pressure) rather than putting a band aid on it?

Exactly, I don't have any problems starting my car after it's been sitting overnight and the fuel pressure has bled down. I know Oldman doesn't either and he has a Aeromotive AFPR.

I think I know the electrical system as well as anyone but I'm not about to sit down and spell out a fix for something that really doesn't seem to be a problem.

Steve

 

[turbosax2]

SFRacingGST,

Lately my brother (snowborder714) and I have been piecing together a complete fuel system for his 95 GST (including lines, pumps, afpr, injectors etc.) to be installed in the somewhat near future.

My brother currently has nothing installed but an intank fuel pump - therefore, the afpr is not giving him a problem currently because he does not have one.



steve,

We have read on numerous posts that that Aermotive afpr's do not hold the fuel pressure and will drop to zero in roughly a few hours. People complain that if they let their car sit for a few hours then try to start it, it takes a few more cranks than usual to get it started.

Again, neither my brother or I have any experience with an afpr - we can only read what people have to say on this forum and take thier word for it. It may turn out that the switch is not neccessary for us. However, we are trying to plan ahead and get some ideas in case we do need a switch. If you would like to help us locate the wire we're looking for, both of us would appreciate it and I'm sure eclipsh would too. If not, that's fine too. Even if we do not have a problem with the afpr, we have read about other people who have and I'm sure they would also benefit from your advice.

Please, do NOT turn this thread into a discussion on need of external pump or need of the switch. I am just interested in how to wire them correctly in case we do decide to go with an external pump and/or switch for the pumps.

No disrespect to either of you, we are just trying to plan ahead in case it turns out to be a problem.



eclipsh,

Thank you very much - you have been a HUGE help getting us on the right track and sharing your thoughts.

 

[compression]

why dont you just leave it the way it is stock and just put a button from a 12vsrouce-button-86 (splice into the existing wire ) and you can just hold the button for priming purposes and then when primed start the car normally and the fuel pump will turn on and off when you want it to.

 

[turbosax2]

why dont you just leave it the way it is stock and just put a button from a 12vsrouce-button-86 (splice into the existing wire ) and you can just hold the button for priming purposes and then when primed start the car normally and the fuel pump will turn on and off when you want it to.

Because I think that would allow the fuel pump to be ran when key is in "off" position or not in ignition switch. I don't want to be able to do that. I think right now the best solution is eclipsh's idea about using one wire - just have to find that particular wire now.

 

[steve]

tAs stated in the article, there may be a wire from the ECU that would work better than the heater relay, I just haven't gone looking for it. With the setup I used any wire that goes hot when the key is in the "ON" position works just fine.

I'd be very happy to hear of a wire that does work better, and will add it to the tech article with credit to the one who finds it

The output of the MPI/MFI relay to power the ECU is the closest, It comes on when the ignition is switched to run and stays on during cranking. Hooking a momentary switch up to prime the pump off this lead is safe but hooking a toggle switch up to run the pump isn't. If the get into an accident and the car doesn't shut off the fuel pump like it should because you modified the activation could be risking your life and others, leaving you liable and alowing your insurance company to turn down any claims.

On a 2G, Mitsubishi changed the fuel pump circuit and eliminated the second input from the starter that primed the pump when the starter was engaged. If you think that would solve the problem you could add that back in.

Steve

 

[turbosax2]

Thanks for the info Steve. I definitely want this switch to be safe and have the fuel pump turn off if the car shuts down in an accident. I'll seriously consider your idea when the time comes for the switch. Do you know for sure that the MFI relay will still supply power to the ECU if the engine dies? Thanks!