Fitness Stain

basically just as the title says ...

how rich am i going to run if i re-wire the pump to see a constant 12 volts?

im want to rewire it while the car isnt running, but if it means im going to be fouling up sparks plugs extremely prematurely , and bogging my system down then i will wait till i get my safc (which will be a few months)

the only problem with that is if i dont rewire it, im scarred i may run lean and pop the motor ..

im not planning on being hard on the car yet, but i think the re-wire is a good preventative mod , but i dont want to do it if im going to run extremely rich

i want to hear from those that have re-wired .... i need to know how rich i really will be running

Scott 89t2

why not rewire it right and use the resistor relay?

Fitness Stain

yeah, ive been reading up on it now, and it seems as though all should be good

edmcguirk

The pump supplies volume. The regulator supplies enough resistance to create the right amount of pressure.

As long as you don't overpower the regulator, your engine should not notice any difference. Your regulator is constantly changing the resistance/pressure to perfectly match your throttle opening so it unlikely to be overpowered.

However your pump will be working at top speed all the time.

It's going to get tired...


ed

Fitness Stain

yeah .. it will be replaced with a walbro before june, so surely it will last until then..

NZConvertible

Not quite true unfortunately. The FRP responds only to manifold vacuum (not throttle position), so it cannot compnsate for any changes in upstream pressure from the pump. If you increase the pump voltage, you will see slightly higher fuel pressure and you will see slightly richer mixtures. This has been verified with a wideband.

I don't recommend feeding 12V to the pump all the time simply because there are no gains, only losses. The ECU has been tuned with the change in voltage in mind, so all you're doing is making light-load mixtures (the ones you see 90% of the time) richer while full-load mixtures remain the same.

All you're doing is using a bit more gas for no reason.

HAILERS

***This has been verified with a wideband.****

How very, very, true!

NZConvertible

All credit to Hailers for that bit of info.

Fitness Stain

damn you guys rock

but i think my post is mis-worded a little

i was planning on doing it exactly as it is in the write up so i assume it will see 9v at idle and go up from there...
i was just wondering if it got richer at all, but upon studying up a little more i realized it functions the same its just less wire for the volts to travel thus less of a drop off ...

am i right or am i way off?

Scott 89t2

less wire, bigger wire, and less relays ( one or 2 more get bypassed in the process) = less voltage drop as it goes to the pump. meaning you will get full voltage when you need it. instead of it droping off.

edmcguirk

Of course the regulator is supposed to follow engine vacuum but engine vacuum is reasonably related to throttle opening.

If you have measured a difference I have to go with the data but I can't understand it.

The regulator is after the injectors so fuel pressure at the injectors should not be affected. I can imagine full pump power at idle might really be slightly overpowering the regulator and also WOT high RPM might be better served with a high current feed to the pump but a properly working regulator should keep AFR very close to what the ECU is asking for.

What do you suppose is the reason for your measured changes?

ed

HAILERS

I had a confrontation (???)with NZ about whether the afr would change at idle if the voltage at the pump, which is normally about 9 volts on my car, was instead the full 12volts.

So what I did, was fully warm the car up first. Then looked at the pumps voltage at idle and look at the wideband meters reading.

Then I depinned pin 3D, which removes a ground from the relay in the Fuel Pump Resistor Relay package, while the car was still idling.

I can assure you the afr got richer when the full 12 volts was applied to the pump vs when it only saw 9 volts.

Pin 3D on the ECU is what controls whether the pumps supply voltage sees the resistor or not. De-pinning means a full battery/alternator voltage and a pinned 3D means the resistor is in the circuit and the voltage drops to approx 9 volts.

Talking idle here. Nothing else.

Again, engine idling with pin 3D in the circuit and 3D out of the circuit. Engine kept running. No turning the engine off ....pull pin .....restart engine type thing.

Make sense? Note: I did this at least five times hoping it was a fluke. Not a fluke. I lost the bet.

NZConvertible

Just correcting a technicality. I do that.
The pressure at the injectors is affected.
A lot of people misunderstand what the regulator is for. It is not their the alter AFR. It is their purely to maintain a constant pressure differential between the fuel rail and the manifold so that the flow rate through the injectors remains constant regardless of load. The amount of fuel the engine receives (and hence AFR) is controlled by altering the amount of time the injector opens for.
Just like I said. The FPR only responds to manifold pressure, so if you change the upstream pressure the FRP will do nothing about it. It can't.

edmcguirk

OK, you've tested it in the real world and it does raise the fuel pressure at idle.

I'm just saying that theoretically it shouldn't. I'm pretty sure the fuel pump is a displacement type pump. It doesn't make any pressure. The pressure comes from the regulator supplying resistance to the volume from the pump. If the pump gets more current, it will flow more volume and the regulator will just pass more back to the return line.

Idle is the most sensitive region of the engine. Even the slightest changes in fuel pressure will be noticeable. Idle is also the place where the regulater is working hardest, it's trying to bypass the most fuel. Theoretically when the regulator is wide open there is no flow resistance. In the real world the regulator will always have some minimum resistance.

Running the pump on full power will have the biggest effect at idle. Everywhere else will be less, probably a lot less.

Here's another idea, not only is the fuel pump going to work overtime, it's also going to heat up the fuel more (because it's working harder) and more often (because more fuel is geting bypassed and recirculated).

Maybe a fuel cooler would be a good idea.

ed

edmcguirk

Actually the FPR has two inputs.

1 The manifold pressure
2 The fuel pressure

The internal springs and diaphragms are calibrated to always keep the fuel pressure the same amount over the manifold pressure.

If you throw more fuel at it, it will automatically try to bypass more fuel until you get the same pressure.

So increasing the pump power shouldn't change the pressure. (It does a little but it shouldn't)

ed

*a*jones*

i suppose i'll just hop in here....

would rewiring a the fuel pump benefit/hinder or make no difference on a NA? namely mine

HAILERS

IMHO it would be a waste of time. A series four non turbo runs full alternator power all the time, unlike series five non turbos. You've a series five that has that fuel pump resistor relay. Your probably better off leaving things alone.

Then again, you could take a meter and backprobe the fuel pump plug and watch the voltage as you drive the car. At first gently then full bore and see if the voltage rises up to apporx 12v. If it does not...then maybe do the rewire just to get back to normal.

All my cars are series four without the fuel pump resistor relay and I never had a fuel pump problem...with them running a full 12v all the time.

NZConvertible

No, you need to do mechanical work to make pressure, and that work is done by the pump. Regulators simply provide resistance. You need to realise that flow and pressure are inextricably linked. You can't change one without the other also changing.
You are corrrect that the flow regulator will pass more fuel down the return line, but that is because the higher pressure in the rail has pusher harder on it's internal spring and pushed the regulator open a bit further. If that extra pressure can open the regulator further, then it's also present at the injectors, increasing their flow too.

edmcguirk

Flow and pressure are only linked if nothing else changes. The purpose of the regulator is to present a varying resistance so that the pressure remains the same regardless of the flow (within the design parameters of the regulator)

The amount of fuel used is almost directly proportional to the amount of HP produced at any second. You could be driving at 5000RPM and the pump will be delivering a certain amount of fuel. The injectors will use some and the rest must go back to the tank. If you suddenly open the throttle, the RPM hasn't yet had a chance to change but the power has gone up. The fuel injection pulse width has just gone up. There is now a lot less fuel reaching the regulator but the regulator must maintain the same pressure or else the engine will go lean and die. The regulator has to close just enough to keep the same pressure (actually it has to raise the fuel rail pressure so that the pressure across the injectors remains the constant).

The regulator may not keep perfectly the same pressure at all flow rates but it comes as close as possible for a cheap part.

ed

HAILERS

*****All my cars are series four without the fuel pump resistor relay and I never had a fuel pump problem...with them running a full 12v all the time.****

Nothing new here. Just a correction. One car does have a fuel pump resistor relay, the one that is an original 87 Turbo II. The other n/a to turbo is wired like a normal 87non turbo. Just cleaning up my post, nothing else.