Have you Rewired your Fuel Pump ?

[antnicuk]

I\'m looking to run new wires to the fuel pump to keep high current going to it as they apparantly lose power with the stock wiring, on the FD the relay is at the front of the engine bay,  my battery is in the stock location,

just wondered how people had gone about re wiring the pump

[RobbieRX-7]

Dale clark over on the yank site has http://www.clubrx.org/default.asp?id=5&ACT=5&content=71&mnu=5

[antnicuk]

thanks for that Robbie,    i have had a read but i dont understand how it makes a difference, i thought that the main power for the pump *red and white wire)  runs from the relay at the front is the cause of the problem.  

can anyone shed any olight on this?

[Prof]

there is a rewire thread for the FC as well - seems the stock wiring is not very thick and couple with the length of the run, it can lead to a drop in voltage at the pump - instead of seeing 13V or more, the pump might only see 11V.   On the FC there is a Resistor switched in series with the pump at idle and lo load, so the voltage measurement must be made when starting or driving under some load - I\'m not sure if the FD has the same circuit in it ?

[rx7veilside]

there is a thread on rx7club.com...as i understand it u take a feed directly from the live in the fuse box which cuts out all the power sapping bits in the middle ..seems quite straight forward in the write up

[antnicuk]

I think the link that robbie put up is the one that you mean,  he doesnt go from the fuse box, he just puts a live to the circuit relay,  i thought i had to do something like you say, and run a new 12v from the fuse box.

still confused...........

[andysmee]

yeah, the FD is the same, the fuel pump relay drops the voltage to about 6.5V at low revs for some reason. RE:Worx rewired mine with a new relay as they couldn\'t get good pressure out of my wiring even on the Supra pump.
 
Put it this way, after rewiring it, the new pump blew the fuel pump fuse which someone had replaced with a 10A by mistake (should be 20A)...which means that the stock pump on the stock wiring was not pulling the expected current so god knows what fuel pressure it was supplying...

[efiniste]

The wiring from the relay to the pump isn\'t the problem. It\'s the feed to the relay that has the current drop (it goes via the ignition iirc). I put in a new supply line to the standard fuel pump relay which upped the voltage at the pump by nearly 2 volts.

[antnicuk]

The wiring from the relay to the pump isn\'t the problem. It\'s the feed to the relay that has the current drop (it goes via the ignition iirc). I put in a new supply line to the standard fuel pump relay which upped the voltage at the pump by nearly 2 volts.

where did you wire this to and from ?  that sounds like the way it was done in the link above to the rx7 club

[efiniste]

I\'ll take a look tonight but from memory there\'s a good feed, straight from the battery, nearby. Use that to replace the standard feed on the relay. I can\'t remember colours off the top of my head but that link above is pretty much spot on. You\'ll find that there\'s a big supply in that fuse box that you can use (two thick wires running to a metal plate that feeds the other relays in there), rather than running another wire to the battery.

[efiniste]

Just read through that link and the pics have jogged my memory a bit. In that fuse box there\'s an empty fuse holder that receives a feed direct from the battery (via the thick wires mentioned in my last post). Use that to supply the fuel pump relay. It\'s pretty straightforward once you\'re actually looking at it. You just remove the 20a fuse from under the dash and put it into the spare holder you\'ve just used.

[antnicuk]

so to clarify, this is the circuit relay not the fuel pump relay on the slam panel at the front of the car.  Do i leave that one stock then?, i had a look and the wires seem quite thick going to the fuel pump relay.

[Laeeq]

do you have to do this mod if your injector duty is up to mark at high boost showing on pfc commander??  I did rewire the pump on my black car as shown in that link but then had to change the fuel lines on top of the engine as they couldn\'t keep up with the fuel pressure and burst on idle.  I think that mod is done on standard fuel pump.

[antnicuk]

I think the mod should be done to all cars regardless of pump as a bigger pump needs even more juice.  All the pumps are designed to run at their optimum at around 13v, anything less and its not running efficiently.

Your lines bursting is a different issue, this is too much fuel pressure which is controlled by your FPR,  no matter how big you pump, with a good FPR you can run low fuel pressure, if the FPR is too small or their is a restriction in the line then your fuel pressure will go up.  

If they burst after you did the conversion you just needed to wind the pressure back down to what it was before the mod, but it just goes to show you that the conversion works and the pump works better when done.

So did you do what is show in the RX7 club link above?

[efiniste]

so to clarify, this is the circuit relay not the fuel pump relay on the slam panel at the front of the car.  Do i leave that one stock then?, i had a look and the wires seem quite thick going to the fuel pump relay.

Yep, I\'ve not touched the one on the slam panel.

Although the wires going to the Circuit Relay look pretty substantial, the actual wiring path is very convoluted and passes through the ignition wiring and a crummy circuit box before reaching the thick wire that goes into the circuit relay. The wiring mod cuts all of that out.