Rewire Fuel pump.Why?
 

I've seen guys mentioning rewiring the fuel Pump.
Now,I am planning on putting a TII engine in my N/A car using the N/A harness.I will installing a walbro 255.
Question: do I need to Rewire my Pump too?,Or does this not apply if the Car was originally N/A..Thanks Guys,STYX.

Well the n/a does have a fuel pump resistor relay.. I'm unsure... I've been wondering the same thing.

This is something I've been wondering about. My 88 vert doesn't have a fuel pump/resistor relay, and the S4 wiring diagram only shows the TII as having one (pg. 50-34). On the NA fuel system page there isn't one in the diagram (pg. 50-36). Yet, I'm fairly sure I've seen an '86 with the resistor/relay...

2slow4stock, your cars are S5s (according to your sig), so they should all have the resistor/relay.

In any case, the "rewire" refers to running all new wires and bypassing the resistor/relay. If you don't have one, and your terminals at the pump are in good shape, you don't really need to mess with it. That's what my situation is. My fuel pump conections are perfect and I have no resistor/relay.

RotaryRocket88:

Not sure if you're doing this, but to be safe: Don't mistake the fuel pump relay with the fuel injector resistor found on 86-early 88 cars (both NA and TII).

The injector resistor is near and below the AFM, the fuel pump relay I'm not sure.

The TII fuel pump resistor/relay controls whether the fuel pump receives a lower voltage or full battery voltage.

I'll post some wiring diagrams.

In the meantime, something to ponder...will the NA fuel pump supply the motor with enough fuel? (Paging Hailers and Icemark)

Attachment 332995

Above: Fuel injector wiring (NA) without injector resistor

Attachment 332996

NA fuel pump wiring

Attachment 332997

TII fuel pump wiring

Attachment 332998

Easy way to bypass system to achieve full voltage to Pump all the time.

This shows Mazda's earlier setup with the low imped. injectors that required a resistor (which Mazda placed below the AFM). The wiring diagram I've edited is for an NA ('88 shown but edited), but both NA and TII models had this resistor.

Attachment 332999

The S4 coupe NA's do not have the "changing voltage" to the pump. There is no relay for this on S4 NA coupes.

However, I have read somewhere that the verts do. THis is something that was fuzzy for me. I never delved any deeper into this because I don't have a vert.

No, I'm not talking about the injector resistor pack. The fuel pump resistor/relay.

And no, the NA fuel pump is too weak to be run with a TII engine. If you check my sig, you'll see I use a pump out of an FD.

No resistor relay in the S4 verts. Mine does not have one, and there is no plug for it, so I can assume it never had one. I was of the opposite opinion that some coupes might have had it, but maybe it's just like the FSM shows it...no resistor/relays on any S4 NAs.

Left side shows the fuel pump wiring on turbos, right side is for NAs.

Edit: just noticed pfsantos posted these images already.

The non turbo (left jpg) and TurboII (right jpg) for 86-87.

The solenoid resistor is not a part of the fuel pump circuit so it isn't attached.

What was the question?

They rewire the TurboII for FEAR of the fuel pump/resistor relay (TurboII cars for 86-87 1/2) failing to the low voltage positon and or they find there is a slight problem if your driving at night with the a/c on/heater on/headlights on and the voltage at the stock wiring at the pump has fallen to an unacceptable figure. Kabloowi! goes the apex seal from running too lean. Something like that.

EDIT: By popular demand of the dog, I attach a jpg of the Solenoid Resistor. Third jpg.

So,I am Guessing that I can Put My Walbro into my 86 N/A chassis's wiring to supply fuel to the TII engine,and I don't have to Mess with any wiring?(the Walbro Unit I got last year has the Sending unit,etc on it,so it is a Plug and play unit,so to speak).
I will not be using the TII's harness on the engine anyhow.I don't know if that is Pertinent.
and Icemark,seeing this is My thread,originally,Can you tell me the Color of the Wire 1r(ps..Knock sensor)I have to Depin the N/A harness.I know it is on other threads But Since I Posted this one,I may as well ask.Thanks.

Interesting topic, I'm glad this thread popped up. I've seen this topic before but couldn't remember the pros and cons of modding fuel pump wiring. Reminds me to educate myself a bit on it.

My car is in my signature, if I can be of any help I can snap some pics, do some research. I want to learn more about the topic so it'd be a win-win situation

Pop the walbro in and you're good to go.

As for the wire at pin 1R, it's light green w/ a black stripe (LG/B). Here, I just happen to have taken a picture of it. A little blurry, but it's the wire w/ the red tape on it.

You are going to run the car on Megasquirt, right?

If so, the whole thread is irrelevant. :)

You'll be running a new wire from the fuel pump relay at your ECU panel all the way back to the fuel pump. Use 12 gauge, and also bring a ground back there as well.

My tuner had me run a larger guage wire directly from the battery to the fuel pump. Simply used a Bosch relay in between that was triggered by the stock fuel pump power wire so all operated as stock. If you look at the schematic, as it stands power otherwise goes through two relays.

Goal was more consistant power flow to the pump (Denso in this case).

would you want to go strait from the battery or another consistant 12v source? i was just wondering cuz i know the battery has about 13-14 volt while the car is on because of the charging system. is that going to be bad? or maybe wear out the pump pre-mature?

straight from the battery. the higher voltage will help maintain fuel pressure under load. it's not going to damage anything.

sounds good, thats how i did mine and then the next day i was laying around thinking about it and just wanted to make sure. also does anyone know what size fuse i should use for an fd fuel pump? i have a 15a in right now.

Ok,Just an update.
I wired the Walboro Directly onto the Stock wiring,it runs great.
I know because I have had to Reconfigure the Fuel lines a couple times,and there is Sufficient Pressure..Trust me!..(Daddy smells liks gas!).
So in short it is wire up and play on an N/A.

yeah on the turbo cars all you have to do is cut the resistor relay from the front and solder the two sets of bluish wires together. then use the factory pump wire in the back of the car to trigger a relay that pulls battery voltage.

For those of you wondering why the two-speed system exists, here is a major reason why:

https://www.rx7club.com/attachment.p...1&d=1251943994

fuel vapor emissions are a major component of the pollution engines produce. Return fuel systems tend to produce significant amounts of fuel vapor, which the evaporative emissions system (charcoal canister etc) has to capture and feed into the engine. Vapors in the fuel lines also can lead to rough idle or vapor lock, which is why there is a hot start assist solenoid. Running a pump at lower speed reduces the amount of fuel vapors produced.

Returnless fuel systems (like on the Rx-8) reduce fuel vapor even further.

fuel pump voltage changes fuel pump out put (output drops). Thats why its best to run it of a constant voltage source ie relay to battery.

For 89-91 the relay is behind the front head light, far from the pump. I remember people saying the stock unit was not reliable for upgraded fuel systems.

Sorry for bringing this back from the dead. So the gist of it is if you have a S5 (a resistor) you don't have to rewire your pump?

People re-wire fuel pumps because the stock wiring is crappy. I lost an engine because the fuel pump had ~5V going to it even though the FPRR passed the resistance test. Its much easier and more effective to bypass the stock wiring and run a 12 gauge wire from the battery to a relay.

You can re-wire and still keep the resister relay if you are on the stock EMS. Without it the idle AFRs suck, mine idles at 11.0 AFR.

Update,sort of.(car under a tarp outside)..I got the Walbro in,and hooked up,running a parallel fuel setup with an RTEK 1.8 and 750;s..all is GOOD!..I can't wait for Spring!

all S5 and S4 t2's have fuel pump resistor relays, S4 n/a did not and needs to have one wired in the circuit in order to run the right pressures.

adding a walbro to any stock car just makes the car run richer so you also need some sort of way to adjust fuel at the ECU to compensate. rewiring the fuel pump to bypass the 2 stage fuel pump relay also adds even more richness to the fuel mixtures since the pump is now doing even more work than before and raising fuel pressure further.