UrS4boy

Our "091G" fuel pumps need all the help they can get to provide the required fuel for our engines when you are making big(ger) boost levels. The fuel pressure regulator (FPR) is set at 4 bar. This means the injectors are designed to always have 4 bar (58 psi) of pressure differential across them (from the fuel rail to the intake manifold). Fuel pump output is related to the voltage it gets. More voltage (up to 16 V according to a Bosch tekkie talking about Bosch fuel pumps) means more flow and/or pressure. Less voltage = less flow and less pressure. I was seeing 11.82 V at the fuel pump under WOT - maximum fuel requirements before I relayed the fuel pump to the battery (about 5 ft from the fuel pump) and 12.98 V afterwards.

In general you need to have 58 psi plus the current boost pressure available on the fuel rail if you are to have any hope of getting the right amount of fuel to the engine under boost. At 28 psi boost, this is 86 psi on the rail. If your pump is voltage limited and can only put out 80 psi on the rail at WOT, it limits you to 22 psi before you are likely to go lean (the ECU via the O2 sensor will be trying to maximize the fuel delivery but even with the injector duty cycle maxxed out, there won't be enough fuel getting to the engine - the A/F ratio will rise and pinging will start - this will cause the ECU to retard the timing as much as it can until the pinging stops (measured by the two knock sensors G61 and G66)).

Based on the above, if you are making more than stock boost, I would recommend the fuel pump relay solution as one means of trying to get enough fuel to the engine<ul><li><a href="https://forums.audiworld.com/s4s6/msgs/31970.phtml">https://forums.audiworld.com/s4s6/msgs/31970.phtml</a</li></ul>

SA urS4

I dont mean to argue about it I just want to know what im doing to my car is going to work and is going to give me value for money.

I want to understand in my own mind how it works before I put it into my car

Thanx for the info I will definately be doing this to my car

The Librarian

No problems. I am the same way (won't believe anything until I have my own "proof")

spiralsmurf

on the injector drivers. larger injectors are really the solution here as long as you can tune for them. otherwise over-running the fuel pump works too. we dont know what kind of affect running the pump at 15v would over.

boostedQs

I have not gone to this extent with details, but your info is VERY detailed, and many will benefit

VR_Life

With Stock Injectors:
1 Bar Boost = 58.8psi + 14.7 = ~74 psi
1.5 Bar Boost = ~81 psi
2 Bar Boost = ~88 psi

With 42# injectors @46psi (code was designed for 37# @ 58.8 psi)
2 Bar Boost = ~75 psi

Which means the Fuel Pump is only holding 1 psi above stock.

The Librarian

adjustable FPR ($$$?) plus the new software written by ??? for $$$.

Might be okay IF you are still stock and looking for an upgrade (with a turbo). I already had a new turbo, injectors and software for this combo when I needed to try this relay solution.

Dave F.

The Librarian

At some point, the injectors go into a hydraulic lock where they can't move the pintle anymore.

cpayne

My fuel pressure goes from 62 PSI at idle to 82 PSI at 5000 RPM..then dives to 60 PSI above 5000 RPM which causes my A/F ratios to be 14:1. Even if I went with larger injectors and wanted to keep a 12.5:1 A/F ratio it wouldnt work. As my fuel pressure would drop off after 5000 RPM just like the RS2 injectors do...so I would have to run very rich below 5000 to even get to a 12.5:1 A/F ratio above 5000 rpm. Now if I remapped the chip this could be corrected.

However the real solution is a consistent Fuel Pressure of 58 PSI+Boost...and not adjusting for either low voltage on the fuel pump or the fuel pump running out of steam.

So going to start by making sure that my voltage at the pump is NOT dropping off. IF it is then Brian Powell has offered his skills to hardwire/relay my fuel pump to maintain a consistent voltage at the pump per Dave Forgie's instructions. IF this still doesnt fix the issue then I have a Bosch Motorsport 044 Fuel Pump on order. Finally moving to 440cc injectors and a change in software. I am sure it is this fueling issue that is holding me back from my 400 WHP goal.

<img src="http://www.horsepowerinabox.com/HPIAB2/images/fs04_01sm.jpg">

spiralsmurf

picked up a genunine bosch relay with harness on ebay for $5 shipped.