Fuel pump rewire: this look good?
 

Just wanted to run something by you. I found this on my hard drive downloaded from here but I can't remember what post it comes from. Does it look about right for rewiring the fuel pump?
https://i673.photobucket.com/albums/...pumprewire.jpg

Many prefer the simplicity of eliminating the fuel pump resistor. This may result in a richer idle, but if you have an adjustable fuel pressure regulator or a means to tune the computer you can mitigate that.

Yeah it has the benefit of simplicity, however, you're recirculating gobs of fuel at ~43psi sitting at that traffic light and puttering around the neighborhood.

Because fuel normally doesn't recirculate in the system? Is recirculating fuel bad or something? ~43 psi is about 10psi greater than what your pressure should be at idle...(28.4psi according to FSM)

Have you verified that your pump voltage is low or something? Are you Turbo'd? Why are you rewiring it?

The diagram also adds an additional relay and wiring to the system. IMO, most of this unnecessary, unless your running good amount of boost and aftermarket pump(s). Personally, I didn't/wouldn't rewire my car that way. It will probably work, but the voltage to the coil in the relay is going to be getting WAY more voltage/amperage than it needs and could possibly fail.

Good luck though.

How would I go about doing it that way?

Rewiring because everything else checks out ok and I'm only getting just over 5V to the fuel pump.

More recirculation increases HC vapor emissions as hot fuel returns to the tank. Removing the resistor also increases fuel pump noise. While those are lesser concerns for many of us, there is a chance that idle AFR will become richer without some other measure being taken.

https://www.rx7club.com/attachment.p...1&d=1268778622

Got it hooked up this way and the voltage to the pump is a lot better. Is an adjustable FPR an easy thing for these cars? May seem a silly question, but the stock one seems pressed into the fuel rail so wouldn't be easy to remove from the system. Or am I thinking about it the wrong way?

for a FPR, you can either use a S4 fuelrail, modify the rail or go aftermarket...

Or I could use something like an SAFC and just get the ECU to compensate for the increased fuel pressure that way, right?

Is this an s4 or s5?

With that you can add more fuel.
But higher fuel pressure does not only provide more fuel, also the spray is better which also helps in better combustion...

But i would recommend a fpr anyways, i had detonating issues with stock fuel pressure when i started to upgrade.

S5

Sorry for being dumb but are you saying the higher fuel pressure will cause better spray and combustion? If so I'd have thought that would decrease detonation issues.

thats exactly what i said...

i raised fuel pressure and had no more detonation

Sorry to bump this thread from the dead, but does anyone know if the modified diagram arghx posted still retains the safety feature where the pump will shut off in a crash/rollover?

Im running a large streetport and an FD pump and have noticed AFR's have been eerily lean. (14-15) under load.

Measure my voltage between the blue and black at the fuel pump connector and im seeing 7~8.2v at idle and 8.7 under load smh....

Yes it does still include that particular safety feature.

Thanks for the fast reply

a) you don't necessarily need to bypass the resistor relay by the RF headlight, just use the original power wire to the pump to turn on the relay.

and

b) if you have an S5 and are using an upgraded pump you should bypass the OEM bulkhead connector.

ok understood. makes sense. im running an S4 fwiw.

so just for clarification, either methods work just fine, just one retains the resistor to lower voltage to 9v and the other is if you want to do without.

now maybe im being ocd but is that a 5 pin relay in the diagram or a 4 pin with just a random line unused line in the center?

One small suggestion: The wires to Pin 86 and 85 should be switched. Pin 86 should see the switched voltage, and Pin 85 should see ground. If your relay has resistive suppression across the coil (like most of them), it probably doesn't matter. But if you use a relay with diode suppression, it'll short the leads and something upstream won't be happy.

Bringing back an old thread so I don't have to make a new one.

Can anyone tell me the location of the harness in the engine bay that needs to be cut to bypass the resistor? I am about to rewire my fuel pump according to the diagram (taking Elwood's advice into consideration).

And just to be clear, I will be adding the relay, not using the factory relay. Is this correct?

That plug is at the resistor box. The resistor box is a grey aluminum box underneath and in front of the factory airbox, bolted just behind the passenger side headlight.

And yes, elwood is correct. Pin 86 should receive 12v and 85 ground, not the other way around.

Thank you!

You are welcome and by the way...

I personally have no issues with the factory relay, and find that adding another one is simply redundant.

EDIT: also I want to mention, instead of running shit to the battery, there are very large 12v fused wires at the ignition switch. I will never understand why people run wire to the positive battery post (audio amplifiers excluded). You have huge 12v positive wires at the ignition switch that are already fused and are located in an inconspicuous location!

I'll keep that in mind. What does it take to get to the ignition switch? My S4 has a mostly mint condition dash, and I'm afraid of things disintegrating if I try to remove anything.

Remove the knee bolster. It's the large panel under the steering column, that your knees would smash into if you got into an accident without a seat belt. To make things easier, also remove the steering column cover (careful! this one is brittle).

The ignition switch has a long harness coming from it, which then connects to the car via a molex connector. You DO want to connect wires on the car side of that molex connector, or you will hate yourself if you ever need to replace the ignition switch.

If I remember correctly, there is a big Black/Green wire that is 12v constant.

Just unscrew the clamshell column surround trim and the back of the ignition switch is right there.

See my post above clocker. If he tags it there, it makes life difficult if he ever needs to replace the ignition switch.

The two "harnesses" involved are the fuel pump and the resistor in the engine bay. For the fuel pump pull the hatch Harper up and your will see the wiring. Just follor it 12inches up and you will find the 4 pin plug. The one in the engine bay is behind the RF headlight where the stock airbox usually sits

My TII has low impedance injectors. Is it still ok to cut all of the wires at the resistor, or will that affect injector operation?

The fuel pump resistor and fuel injectors have zero relation to each other electrically.

Just don't snip the wires so close to the plug you can't wire it up stock again if you need to.

I made jumpers to fit inside the plug, so I can just plug it back in later if I decide to go back to stock. I'm working on wiring in the relay now.

Ok, one last question (I hope). If I am reusing the stock relay, which wires (colors if possible) do I connect? I can't find a good breakdown of the wires in my Haynes manual.

It has 6 wires, 2 connectors.

4-pin connector: fat blue, small blue, fat black/yellow, small black.

2-pin connector: small black/yellow, small white/black.

^ The relay I listed is the EGI main relay on the driver side, between the strut tower and firewall. I couldn't find anything on a fuel pump relay.

What do you want to do to the main relay?

The 4-pin relay in the diagram. Pins 30, 85-87. Is that a factory relay located somewhere in the car, or do I need to supply my own relay? I was assuming it was a factory relay based on the specific numbers listed.

If you're talking about the relay used in rewiring the fuel pump then that is a different relay than the main relay, thus you supply your own.

Ok, thank you. Is there a common aftermarket relay that everyone uses when doing this, or do I just pick up a 4-pin relay from auto zone?

You would use a standard automotive relay found at an auto store.

Perfect. Thank you again.

I got everything wired up today. It starts and idles like normal, but throttle response has improved, there's no more hesitation when I blip the throttle, and it doesn't act like it wants to die when taking off anymore. I didn't notice the 3800 rpm stumble anymore, either.

One thing I did notice, though, is that the relay I added got very hot to the touch. Not hot enough to burn my hand, but not far off. Is this normal?

What is the amperage rating of the relay. Usually, they will say something like "30/40" with 30 meaning 30 amps constant and 40 meaning 40 amp momentary.

It just says 30 amp. It's tied into a 10 gauge wire with a 30 amp fuse for my aftermarket stereo. Does it sound like anything I need to worry about?

Is it also powering your aftermarket stereo? How do you have this thing wired up, the best that you can explain?

There is a 10 gauge wire with a 30 amp fuse coming off of the battery (put there by the previous owner) that powers the stereo. I teed a 12 gauge wire off of that 10 gauge wire and ran it back to that relay. The relay only powers the fuel pump, the fuse is for both. The rest of the wiring is exactly as shown in the diagram.

I have a saying at work "Never trust anyones connections or terminations".

With that said, a 30 amp relay on a 30 amp fuse that isn't blown should not be getting hot. If it was pulling that much current, your 30 amp fuse would pop, so something else is wrong here.

After looking everything over again, I think the fuse holder is bad. I unplugged the fuse instead of disconnecting the battery to test all of my connections and I was still getting voltage at the pump. I'm going to replace the fuse holder and test everything again.

See, this is why you never trust anyone else's termination or connections.