1.8t fuel pressure

[datmanfpres]

Stock ECU, I've been getting the engine code for "Multiplicative Fuel System Too Lean" for some time now. I have verified that I'm not getting any unmetered air in.

Today I replaced the fuel pressure regulator on the injector rail, and also added a connection for a fuel pressure gauge. Unfortunately I didn't get a reading with the old regulator, but with the new one installed I was getting 3.1 bar with the vacuum hose on the regulator connected properly, and 3.8 bar with it disconnected.

According to the specs I've seen, my engine code uses 4 bar fuel pressure into 284cc/min injectors (also, my FPR is stamped 4bar).

- Should I assume that I have either a clogged fuel filter or bad fuel pump since I'm getting lower?

- Is there supposed to be a check valve on the vacuum hose from the FPR to the manifold such that only ambient or boost pressure gets to the regulator? It seems like the vacuum connected as I have it takes the pressure down quite a bit, though that may be on purpose to make idle injector PWM more fine-grained.

FWIW, the car is a 2001 A4 quattro wagon 1.8t.

Thanks!

[Steve Chicago]

No check valve on that intake manifold to FPR hose. That pressure signal is used to bring fuel pressure up or down depending on what the engine is doing. At closed throttle, vacuum hits the FPR and fuel pressure is reduced from base pressure. As you throttle up under load, boost pressure hits the FPR and it adjusts fuel pressure higher than base pressure.

The pressure setting of the FPR is measured with no pressure signal connected. This is the base pressure with no compensation adjustment. Your 4 bar FPR should produce about 58 psi like this. Is your pressure gauge accurate?

How many miles are on your fuel filter? They aren't crazy expensive and not too hard to change out. It never hurts to get a fresh one in there if this one is unknown.

A good way to determine if you've found all air leaks is to do a boost-leak-test. Some leaks are hard to find otherwise. Another thing that can effect Multi Fuel Trims is a bad or dirty MAF.