Who's installed an STi Fuel pump? Strange behavior

[winston856]

So I installed a used '06 STi fuel pump with 10k on it into my GT last summer. Everything plugged in fine, it was a pretty easy install and it runs fine.

I noticed there's a high pitched whine coming from the pump when the car's running. You can hear it if you're outside the car standing behind it at idle. It's quiet but there.

Other thing is I used to be able to run my tank dry. I mean the gas light used to come on and everything. I used to be able to run it down so I could fill it up and it would take like 14.5-15 gallons.

Now with the STi pump in there I can run it low enough so the gas light barely turns on. If it gets to that point the car starts acting all weird, loss of power etc. Like the pump is sucking air. Also if I run the gas down to where I used to be able to the car won't start on the first try. I have to let go of the key and crank it again so it'll start up. Again this is only when the gas is running low in the tank but not as low as I could get it before.

I liked using my gas light and am confused why changing the pump has made this big of a difference.

Is this just the results you get of installing an STi pump into a GT tank? Can somebody shed some light or speculate or SOMETHING? :smt021

[mike-tracy]

I've heard the same things about the sti pump from others - not being able to use that last bit of fuel in the tank. Did you just swap the pump, or the float valves also? They're probably calibrated for the different tank.

The whine, I would imagine it not being normal - having ridden in and driven in STI's, I never was able to hear the pump. Perhaps they are more sound insulated than your car?

Also, why did you put in an STI pump? None of your mods listed take advantage of it, so while it's not hurting performance, it's not helping either.

[anothernord]

I've got an STi pump. Been running perfectly for almost a year. I never run the tank dry, so I can't speak for that part. There's always the chance that your filter bag fell off so its just sucking straight into the pump.

As for the whine, that's pretty normal. When you turn the ignition on, you can hear it prime, as well as idling.


I've heard the same things about the sti pump from others - not being able to use that last bit of fuel in the tank. Did you just swap the pump, or the float valves also? They're probably calibrated for the different tank.

The whine, I would imagine it not being normal - having ridden in and driven in STI's, I never was able to hear the pump. Perhaps they are more sound insulated than your car?

Also, why did you put in an STI pump? None of your mods listed take advantage of it, so while it's not hurting performance, it's not helping either.

An STi pump can be found for quite a bit cheaper than an OEM replacement, and the increased pressure makes starts easier because it can provide more fuel. At least it has in my experience.

[mike-tracy]

^^ Sure it's not because the STI pump is a decade newer than your old one? :smile: plus yours is supercharged unlike OP's

[ouch1011]

The STI uses a fuel pump resistor in factory form in order to keep the noise down. That's typical for factory f/i cars. Its noisy because it is pumping a lot of gas. In stock form with the sti, the power to the pump runs through a resistor to step down the voltage and slow down the pump for normal driving. When engine load/fuel requirement goes up, it switches a relay on to bypass the resistor and runs full voltage to the pump to get full flow. It is noisy when this occurs, but you don't hear it because you are probably at nearly full throttle and that makes plenty of noise.

I can't answer for the fuel level problem.

Also, fuel pressure is determined by the fuel pressure regulator, not the fuel pump. Putting an sti fuel pump in a legacy will not increase the fuel pressure unless the old pump was bad.

[winston856]

Well thanks for clearing the noise part of it up.

I installed the pump + filter bag so I did not reuse my old bag. I did it because my old pump was stock and I had reason to believe it was failing. I got the STi pump for $35 so it was a good deal.

Now I just need to figure out why I can't run it down as low as I could before. It's like the STi pump is shorter and can't reach all the way to the bottom of the tank. Maybe the bag did fall off? That could affect it's ability I guess.

I remember when switching the pumps the STi one was much smaller than the GT pump, it sits in the same location though so I'd think it could reach the bottom of the tank.