The relay labeled fp or fuel pressure relay by the bumper is actually the switching relay for the fuel pump speed. The car will still run with it removed, but only get about 9v to the fuel pump. The fuel pump relay is actually the green circuit relay next to the shock tower. Pull the switching relay and make a jumper wire for the back two pins when looking from the front of the car. That bypasses the resistor. In the relay box by the shock tower I perform what Dale Clark describes. I ran 12v to that right from the front fuse box that the positive battery terminal is located on. In the back by the pump I mounted a standard 40 amp relay. I used the stock fuel pump power wire to trigger the relay and ran a 10 gauge power wire direct from the battery to that relay. I also added an extra ground.

 

so it would be smart to do both rewires under the hood and in the back?

 

if you want but just doing the one in the back is enough, unless you are affraid your relay won't be triggered with the 9V the resistor gives...

 

now the only thing that cunfuses me here is, your using the newly run wires to power the pump and the original wires to activate the relay..so

which wires now tell the pump how much fuel to bring up front since the R/W wire has been bypassed?

and is there anything else you have to do to that R/W wire upfront to get this working properly?

i probably missed this part but i just want to clear that up before i do this

 

Any of you ever consider running the fuel pump straight off the battery? That's how mine is wired. I have a switch though.

 

Rotary Experiment Seven- how many hours of labor to do this?

 

The LS1 swap guys have been doing this for awhile now.

 

Its not always necessary to rewire the truck/pump area. The main issue is the 9v/12v switching and the resistance through the ignition switch. Doing the Dale Clark under the hood bypass to the battery increased my fuel pressure dramatically and I ended up having the retune the car completely!

The wiring to the trunk should now be carrying 12v consistent. If its not, then I would consider the relay+10gauge wire back there...

 

Strictly speaking, the value of the fuse is set to be appropriate for the expected total current. Bringing the voltage at the pump up from 11 volts to 14 volts will only increase the total current by 3/11 = 27%, not enough to justify a 50% increase in fuse amperage, especially considering that the fuse was designed for a circuit with 14 volts at the pump. The fuse IS there to protect the wiring, in case of a short circuit at the pump or between the fuse and the pump, but there is no reason to up its value from 20 amps to 30 amps just because the wire is heftier.

 

my mechanic told me he's being doing this to every car... is this enough or do i still have to rewire the fuel pump?

 

I did the same thing. Very easy job since my battery is sitting behind the seat. I have a 30 amp switch without a relay.

 

Essentially a relay is a switch. But I prefer to use a relay to keep things more automated. My battery is also now located behind the driver seat, which allowed me to get rid of several feet of the wire going from the back to the front.

Also I see nothing wrong with running a 20, 30 or even 40 amp fuse on a heavier gauge wire. I'm running dual pumps so the load is going to be higher in my case. I can't remember what fuse I put in there but it's been holding.

 

Sorry for the late response. About 1.5 hours labor if your battery is in the trunk or bins. More if I have to run a power wire from the front of the car.

 

A side note to add, not sure if this has happened to anyone before. But we did the same mod to a friends FD and for some reason deiced to use the same stud/bolt that the fuel gauge sensor was grounded to. The fuel gauge did not like that at all. So please when looking for a new ground don't use any existing ones near the fuel pump as you might grab the fuel gauge sensor ground. This was on a 94 R2, so I'm not sure if the ground location for it changed between models?

 

Sorry to bump this up but i am about to rewire my fuel pump and install a KB boost a pump and saw that thing about the resistor. You don't have to jump that if you are running a new wire do you? Since that wire will just be activating a relay to send power to the fuel pump so as long as it gets voltage(low or high) it will be fine right?

 

Correct.

 

hi guys,
if i understand corectly , if someone do this rewiring that means that the resistor pack will stay off and the pump will get a constant 12v . is this correct?
my questions are:
1) is there any problem to the pump if it gets a constant 12 v all the time ? mazda says that this resistor helps the pump life.is it true or it is another stupid thing on the car?

2) if i make the mod and run the heavy gauge wire from the bat to a new relay , do i need to make or jumper something at the resistor circuit?

3)can i place the relay in front beside the bat?i am thinking that as an easy if i need to have a look and check the relay.that means i must find the wire that goes to the pump at rear.any ideas?


thanks!!

 

1) one of the reason they had the resistor pack was to improve fuel economy. Many older rx7s get a constant 12volts to their fuel pumps without a problem.

2) yes make a jumper wire for the plug that used to be plugged into the resistor pack

3) relay placement is not as important as size of the wire.

 

^ The resistor pack was also their to improve pump life.

thewird

 

"2) yes make a jumper wire for the plug that used to be plugged into the resistor pack "
do you mean to completly remove the resistor and its place to fit the jumper wire?
if i remove the fuel pump relay that controls the resistor and jumper it i will have the same result?
i am refering to the page F-108 from the workshop manual.
in that diagramm it seems that the fuel pump is also wired to the cirquit opening relay.that means that when i turn the switch to the "On" position i will have the pump working all the time?



thanks

 

^ If you jump it, there is no longer a need for the resistor so you can save 1 pounds by removing it lol.

thewird

 

Could you source the FP signal wire before all the stuff in the engine bay, and just run it to the back to the new relay? It's the red/white wire in the drawing above.

 

why would you want to do that? you already have a wire in the back, what is the point to take a wire in front to run it all across the car?

Also, someone up there said the resistor ir for fuel economy, it has nothing to do with it, it is for fuel pump life. Otherwise, you would have to show me how it affects fuel economy without changing the fuel pressure.

 

cpnneeda:
i do not want to run the fp signal wire to the back. i will put the new relay in the front and i will run the heavy gauge wire to the pump in the back.

puma:
yes it is for pump life. i wonder how this will affect the pump life.
do anyone know how other cars wire the pumps? the resistor for low load is mazdas invention or it is common?

 

I say it affects fuel economy because it keeps the stock pump from running at full speed. Even in full boost conditions. Have you ever measure the voltage at the pump when in full speed mode? It will be less than 12. Some where around 11.2-11.5 range. That is not good in my books. And may lead to lean conditions. Anyone that has done this mod knows that once done the entire fuel map has to be readjusted because of the extra fuel. Now whether this is a problem with the fuel pump over powering the stock regulator. I do not know because I don't have a way to measure pressure right now. But I do have the stock regulator and a PFC/Datalogit and can tell it you it affected the entire map. And I did not touch the regulator.