Help needed to understand fuel pressure gauge readings

[Jonas_R]

Oki my car is running **** rich at the moment.

Running 044 fuel pump with 7A 4bar FPR.

So I installed a fuel pressure sensor from Zeitronix where the fuel enters the fuel rail.

The sensor has the following specs:

Sensor 150 PSI Gauge
Output 0.5 volts at 0 PSI gauge pressure (atmospheric pressure)
4.5 volts at 150 PSI gauge pressure (150 PSI above atmospheric pressure)

At idle the gauge reads 3.5-3.6 bar which seems correct.

But at WOT with 1.7 bar boost (relative) the gauge reads approx. 5.3 bar

Now I'm thinking this is way to much fuel pressure since a 4bar FPR should regulate the pressure to 4bar. But after reading S2central.net thread "fuel pressure revisited" I'm just confused to be honest.

So can anybody help me out to understand how this work?

[UrS4boy]

....At idle the gauge reads 3.5-3.6 bar which seems correct.
But at WOT with 1.7 bar boost (relative) the gauge reads approx. 5.3 bar
Now I'm thinking this is way to much fuel pressure since a 4bar FPR should regulate the pressure to 4bar. But after reading S2central.net thread "fuel pressure revisited" I'm just confused to be honest. So can anybody help me out to understand how this work?

A fuel pressure regulator (FPR) is supposed to regulate the fuel pressure ACROSS the injector, i.e. from the fuel rail to the intake manifold. A 4 bar fuel pressure regulator at 1.7 bar relative boost should show 4 + 1.7 = 5.7 Bar at the fuel rail.

At idle, your engine will be making about 1 Bar vacuum so the 3.5 to 3.6 Bar in the fuel rail seems about 0.5 Bar high (= idleing rich?). In contrast, the 5.3 Bar at 1.7 Bar boost seems about 0.4 Bar too low. Are you sure the FPR is in good condition?

[Jonas_R]

Ok so a slight fault in my calibration of the map sensor, forgot that it was 0 PSI at 0.5V and 150 PSI at 4.5V after these adjustments. Fuel pressure is 81.25 PSI at WOT with 25 PSI pressure, so that is close enough.

Same goes for idle I'm only getting around 10 PSI vaccum and fuel pressure is 49 PSI so that is fine as well.

So FPR seems to be fine and thanks for the help clearing up how the fuel pressure works.

[UrS4boy]

.... Fuel pressure is 81.25 PSI at WOT with 25 PSI pressure, so that is close enough. Same goes for idle I'm only getting around 10 PSI vaccum and fuel pressure is 49 PSI so that is fine as well....

1 Bar = about 14.5 psi so 4 Bar = 58 psi. Therefore at 25 psi relative boost, your fuel pump needs to be supplying 83 psi. If you are only getting 81.25 psi, you are likely going to be running lean at WOT. Are you getting any pinking?

The cure is a 044 fuel pump.

[Jonas_R]

I'm already running 044 fuel pump and I'm running 10.4 AFR at WOT so not running lean at all.

Just installed the fuel pressure sensor to make sure that pressure was correct

So likely it is the fuel map causing these problems.

[chipsenter]

My suggestion bro, use stock 3,5 bar from ABY engine then u dont need to use time on reading all different guages

Im using Automotive parts at my fuelsystem , only running 3,5 bars on idle like u.

Not necessary with more if u not aiming "big time"

[Knight Rider S4]

My suggestion bro, use stock 3,5 bar from ABY engine then u dont need to use time on reading all different guages

Im using Automotive parts at my fuelsystem , only running 3,5 bars on idle like u.

Not necessary with more if u not aiming "big time"

What set are you using?

Injectors
Turbo
Map
Fuel Pump

[chipsenter]

Todays spec.

Siemens 903 cc
Turbo netics super 60
Autronic Sm4
Maf not necessary

-----------------------
Last spec .

4" Maf
Siemens Deka highout 633cc
Turbonectics E50
Special SW for motronic 3 bar map
boost cntrl.
typical 500hp kit

[UrS4boy]

My suggestion bro, use stock 3,5 bar from ABY engine

Er, since when did the ABY come with a 3.5 Bar Fuel Pressure Regulator (FPR)? I am pretty sure the ABY came with a 4 Bar FPR, i.e. the PN is 078 133 534 C, which is the same as the AAN FPR which know for certain to be 4 bar. In fact, if you are getting 3.5 bar on idle, then your FPR isn't 3.5 Bar, because there is vacuum, e.g. -0.5 Bar, on the intake side (3.5 - (-0.5) = 4.0).

In contrast, the RS2's ADU came with a 3.8 Bar FPR (PN 034 133 534 P).

[chipsenter]

URS4 - Im not quite sure when they came with 3,5 stock eh ? I just used the stock one the whole time until I bought the Automotive one.

Keep it up.

J

[UrS4boy]

URS4 - Im not quite sure when they came with 3,5 stock eh ?

The answer is NEVER.

[A80Avant]

jonas with all those aftermarket extra equipment you have it is pretty much unnecessary to get VEMS now!
all you need is a good timing map by somone that can do that in the motronic,and you can decide on fuel and boost thereafter.

really,motronic can do gross adjustments on spark as well, so you'll be safe for knock!!

[Jonas_R]

Yeah I just got the car remapped today by Mattson in Sweden and it goes really nice now
I think I will just let Mattson map the car when I get the new turbo, had a talk with him and he said that it would not be a problem

[chipsenter]

Nice u got it fixed.

Anyway, if you running 3B engine or ABY,AAN , ADU etc. u got the pro's in Sweden called TURBOCENTER Stockholm . No one understands the Motronic like them i can guarantee that.
They built SW's to the fastest blackrace audis in Sweden

Like u say your aiming about 400-450hp , TC has ready kit to you ,
Maf, FPR,SW,Injectors, just plug and play and fill gas.

Keep it up

[chipsenter]

The answer is NEVER.

I had it on my S2 1994 ABY pretty much stock for me when I bought it couple of years ago.
Anyway doesnt matter if it came stock or replaced one , the answer here is that it's plenty with 3,5 bar fpr on a 4-450hp and more.