Fuel pressure question

[Shadowv4l]

My friend has a 2004 Jetta GLI, he thinks he is having some fueling issues and has an aftermarket secondary pump in line mounted in the engine bay. He has a guage right before the secondary pump and one right after the secondary pump. The gauge before it while the car is running shows 0 psi and the guage after shows 40ish - is this strange? From my understanding the stock pump in the tank should make 36psi on its own so why is it at 0 now? He disconnected the secondary pump and the gauge before it read 50psi and the guage after reads 40psi. He tried disconnecting the primary pump while the car ran to see if the secondary pump could run the car but it ran out of gas (makes sense). He "needs" the secondary pump because he is running big turbo big injectors. I told him screw the secondary German wetdream and just put a Walbro in the tank and call it a day, not sure why Vdub has to be so effin difficult all the time!!!

Also - when he turns the key on and primes the primary pump (in the tank) it only builds about 8 - 10 psi. So i guess my question really is.... is their enough fuel being delivered and does he really need this secondary pump crap?

[AZTurbo]

Sounds like the up-stream pump (closest the engine) is out-flowing the down-stream, basically causing a 'vacuum' effect on the tube between the two, resulting in zero pressure reading. Sounds like the down-stream pump (closest the tank) is a bottle neck. Just put a single pump in it and call it a day. Unless it needs a boost pump for some reason? Is it an OE setup?

[Shadowv4l]

the pump in the tank is an upgraded pump and the pump in the engine bay was added with the large turbo kit

[AZTurbo]

Then it sounds to me like my thinking is accurate, the in-tank pump isn't up to the task of providing as much flow as the underhood pump. Not sure it's an issue unless there's a driveability problem?

The pump under the hood would likely do better without the in-tank pump. Pumps provide flow and pressure, some are better at one half of that than the other - that's why our early TD's had two pumps. One for pressure for the EFI, and one for flow to feed that EFI pump. Obviously, technology has progressed and a single pump should be more than capable of providing both pressure and flow until you get they very high power output levels.

One in-tank hi-flow pump should do the trick, IMHO.

[Shadowv4l]

I was trying to get him to go that route, we will see what happens. Thank you for re-assuring my thinking. It just seems stupid to me to have 2 fuel pump because if either of them drop out then you're screwed - double the components double the failure possibility.