Just curious if it will be ok to put a walbro 255lph fuel pump on a stock n/a S4 and not have any problems driving the car daily? Just curious cuz my friends fuel pump went out and he would rather just get the walbro in preperation for the turbo swap.

 

ummmm

 

It will run incredibly rich. Like, "don't do it" rich. I'd try to find a good used pump if you won't be using it for long. Hell you might even be able to find someone who will let you borrow one from their non-running car or something.

 

wouldn't the ecu only allow the injectors to only flow the same amount as before through the the same stock tune?

 

The ECU will control the injectors for the same timing. For example, if the time is 5 microseconds, it will still only pulse 5 microseconds. However, the Walboro will send the fuel pressure up, so more fuel will get out in the same amount of time.

 

It'll be fine short term. Expect power loss, poor MPG, and a lot of carbon.

 

oh, that makes sense... well that just gives the guy a reson to mod it even faster lol

 

this is true.

think of it like having a garden hose nozzle turned on just a little bit and turn the water on just a little at the faucet, only a little will come out. now crank up the pressure at the faucet and you will see more water pressed through the same opening because the pressure is increasing.

 

hey fool why didnt you call me back when i called and texted you?

oops i mispelled "reason" above

 

Sorry to threadjack but while on topic, how much MORE does a Walbro 255 flow than a stock turbo II fuel pump? Mine got swapped by PO and my AFR is on the rich side, but not crazy, was wondering if getting an adjustable FPR would work?

Running 12psi, FCD, stock n370 on a properly converted 1990 GTU with a S4 keg and S5 electronics/intake, streetported, on a 2.5" straight-through exhaust into two magnaflow canisters at the back.


Also maybe you should just spend a little money and buy a stock N/A pump from someone off the board?

 

I think the stock TII Fuel pump is somewhere 160-165lph IIRC. Not 100% sure.
If your running rich, I recommend having some sort of EM and getting it a tune.

 

yea as said before i would only get it in prep for the tII swap...once i put mine on i fell in love with it...however...now that i think of it...it does run a little rich...lolz.

 

So....what's the purpose of a fuel pressure regulator?

 

It regulates the fuel pressure.

 

The Walbro will flow more then the stock FPR can bypass. This results in a higher fuel pressure than spec, at least at idle and low speed operation. Aftermarket FPR's are able to handle the flow.

 

my battery is dead and i can't take texts until i fix the touchscreen on my phone.

a regulator is a restrictor as well, the more pressure there is behind it the less it can control pressure. install a high flow fuel pump and you will see pressure rise just from the additional pressure the pump is pushing.

 

Here's what a Walbro pump does to fuel pressure on a system using the stock FPR. Atm = atmospheric pressure. I tested this last year when I was troubleshooting mixture issues.

Walbro GSS-341
Idle: 46 psi
Atm: 48 psi
10 lbs. "boost": 54 psi

FD pump
Idle: 34 psi
Atm: 41 psi
10 lbs. "boost": 51 psi

Idle spec alone is roughly 30 psi, so the walbro is jacking the pressure up about 16psi over stock! My idle AFRs went down a full point at idle with the walbro in the car. You can see as the pressure rises, the numbers are closer stock (stock is about 30/40/50 psi in this case). Under boost this can be fine, but when it comes to idle and low throttle situations, the walbro just flows way too much for the FPR. In other words, this is not NA engine friendly at all.

 

The walbro pump is badass, but it won't save you from leaning out if you crank up the pressure. At 10psi on my STOCK TII engine with STOCK fuel injectors, it creeps dangerously into the 13.. dare I say 14 AFR range. This is why I had to port the wastegate. It's free and I didn't have the money to fork out for larger secondaries at the time.

Just to clarify, the fuel pressure regulator restricts the fuel after the injectors, so on the RETURN side. So in essence, it restricts the amount of fuel making it back to the fuel tank. At idle, it should have the most vacuum, so it'll open the FPR up more, and allow more fuel to return to the gas tank. At WOT, it should have 0 vacuum (NA) or pressure (turbo). Therefore, the FPR closes, allows less fuel to get back to the fuel tank, and more makes it through the injectors. Like the Karack's explanation about the garden hose, it can be related to the FPR as well. More pressure, same restriction for both the injectors AND FPR. So, you'll have higher fuel pressure at ALL times, and much more fuel cramming itself through your injectors, causing (as stated before) worse gas mileage, crappy performance, and more carbon.

And getting an adjustable FPR will not help. So far as I know, there isn't one that can actually lower pressure. I tried it on my NA, and went right back to the stock fuel pump, and held on to the walbro until I got the TII drivetrain.

 

OK got it. Thanks! I appreciate all the help. He still bought the walbro and gonna hold on to it for the swap. LOL

 

i've cranked out over 400 wheel horsepower on the walbro 255LPH pump, it can easily handle the boost of a stock turbo power output. if you don't have a way of adjusting fuel injector bandwidth then the pump can't be fingered as a problem. if you did in fact have a way of adjusting the fuel injectors output then you probably had old craptastic wiring to your brand new shiny high output pump. it is common after all and why many tuners recommend rewiring your pumps. i had one S5 turbo 2 with a T70 that was dropping voltage down to 6 volts! and it still was making well over 300 wheel horsepower at that point..

simply adding a pump to a near stock car isn't going to miraculously allow it to run safely at 14PSI on the stock fuel maps, the car isn't even meant to see 10PSI, that is why it has a boost cut built in.

 

Dang this thread turned into much more than I expected. I'm learning a whole lot right now.

 

You're about to know further...

The stock FPR runs rich with the Walbro because it cannot bypass enough fuel to keep the pressure down. An aftermarket regulator, assuming it is sized properly, does not have this limitation and will easily be able to keep the fuel pressure at a stock level with a Walbro or any other large pump.

 

that depends if the stock FPR is installed still, some people leave it on and unplugged and use the aftermarket FPR to raise fuel pressure.

 

So you could leave the stock fpr installed and disconnect it and then use an external aftermarket to keep the pressure in check? What is the pressure I am want to stay at?

 

If you leave the stock fpr in place (adding the aftermarket fpr in the plumbing after the stock fpr) you will still have the rich idle and low speed issues. Listen to what Aaron said and what I said earlier in the thread: the stock fpr cannot handle the extra volume pumped by the Walbro . It doesn't matter how low you set the aftermarket fpr if the oem fpr is still in the fuel circuit.