S4 wont start - which fuel pump?

[rjpiselli]

2004 S4 - MT - 100k miles

always ran great. the other day it started and ran really rough and stalled. it wouldn't start, just turned over. I lifted the back seat and pounded on the fuel pumps with my fist, turned the key and it started and ran great. (pounding may have been coincidental) No vcds codes.

today it wont start. just turns over. I unscrewed the rubber fuel line from the fuel rail and no fuel came out. turned the key to the ON position and no fuel came out. held the key in the START position and no fuel came out. Fuel filter has approx. 3k miles on it.

so it's def fuel pump. my question is which one is it? There is a fuel pump on each side of the car under the back seat. To my knowledge the fuel pump on the passenger side is the MAIN PUMP and the one on the drivers side is the TRANSFER PUMP. but I've also read somewhere that suggested the transfer pump kicks in during starting as well. So I'm not sure which one I should replace, and based on the vehicle having absolutely no fuel pressure during cranking which pump that indicates is bad.

any help is appreciated. thanks!


**also if anyone can comment on the quality of the fuel pumps on ecstuning i'd appreciate it, as the fuel gauge always has been accurate so i'm likely just replacing the pump.

[B6_4.2]

What is your fuel level? If it's not low then it should just be the main pump. The transfer pump (to my knowledge) only transfers fuel to the main pump, meaning that the main pump is the one responsible for fuel pressure

[rjpiselli]

It has a half a tank of fuel at the moment. I kinda thought the same as you're saying in regards to the roles of each pump but I started second guessing the theory when I read another post that said the transfer pump AIDS in starting. But I'm thinkin that was a post from someone who many not have been quite sure about the duties of the pumps.

Thanks for the reply.

[rjpiselli]

For anyone interested, I am replacing the passenger side pump. ECStuning has pumps only, not the whole assembly, and after looking closer at them I realized they are high flow pumps that are not direct fit. I found them ranging from $425 (JHM) to upwards of 5 and 600 plus shipping.

Partsgeek.com has them brand new for 316 and a coupon code for 15 off 300 or more plus free shipping. So looks like a pretty good deal. Will be installing probably this weekend pending arrival.