s5 TII fuel pressure question

[RETed]

Originally Posted by NoDOHC

The FPR regulates fuel pressure by dumping fuel to the return line. If the pump is flowing more fuel than the FPR can handle, it will not be able to regulate pressure. The fuel pressure falling when under boost is an indication that this is the issue, as the injectors are using some of the fuel from the fuel pump, allowing the FPR to dump enough.

I would look into replacing the FPR with either a bigger aftermarket one or a newer (FD) stock one. I have not had this problem, but I have never required a bigger fuel pump than stock either.

That doesn't make sense?
The FPR is a mechanical bleed-off device - nothing fancy.
With the fuel injectors firing, the fuel flow through the whole system is less.
If the FPR is working correctly, this should not be a problem.
The problem arises when there is too much flow, and this "overpowers" the FPR - you end up with too much fuel pressure at the rails.

If the FPR is okay, then dropping fuel pressure is indicative of a fuel leak or a bad / failing fuel pump.

It's funny you started this thread...
I have a customer whose S5 FC turbo FPR just failed just like yours, except his was stuck at 60psi at all times.
He swapped it out and running parallel rails with an Aeromotive FPR now.
:P

As another guess at the problem...
Can you confirm the fuel pump is getting "full voltage" at all times?
Run a DMM / voltmeter to the fuel pump leads as close to the fuel pump as possible and monitor...


-Ted