cparke

I finally got the nerve up to disturb the factory installation of the fuel lines in the Engine Bay and install a fuel pressure gauge to diagnose my ongoing fuel trim too rich multiplicative problem.

The results are quite strange, and pressure does appear too high.

Fuel pressure
without the vacuum line connected to the FPR: 64 PSI
with the vacuum line connected (approx. 18inHg Vac) 56PSI.

Fuel pressure does jump as expected when the engine is initially revved.

At engine shutdown, fuel pressure usually (but not always) drops immediately to 42PSI, but then over the next 10 minutes rises to 58-60PSI! How the hell does that happen with everything shut off? Then it will slowly fall over the next few hours, after 24 hours it will reach 0PSI.

Okay, this doesn't sound right to me. It was a rainy day with a LOW PRESSURE atmosphere outside too, if that matters any. Bentley says the specified value without the vacuum hose connected to the FPR should be approx. 3.8-4.2 bar (55.1-60.9 psi). I'm a bit higher than that. It also talks about residual pressure 10 minutes after shutting off the engine being 31.9PSI on a cold engine and 43.5PSI on a warm engine. I have residual pressure rising actually and then taking hours to reach those levels.

Okay, does anyone else agree what I'm seeing is wrong, and any ideas on what could be the cause?

@wesome

Oil temperature Mickey?

MrGoodbytes

Coolant level Pluto

cparke

Clogged fuel return line is my best guess at this point, I need 5 feet of hose to test out that theory.

@wesome

you ruined it

Cab_and_Wagons

over the weekend, and the fault codes reappeared two days later. My current thought is that it's either a FPR, or fuel filter. The fact that it's both banks leads me away from injectors. Good luck.

freakness

Like a stillborn child, the heartache of a life cut short is sad indeed.
























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cparke

Once I nail this problem (and I feel I'm getting really close now), I should be quite the expert and I'm going to post a comprehensive article to the FAQ explaining every possible thing it could be and how to test each one.

In my case, I've fixed some many things other than the actual cause that it now takes 500+ miles to get the fault code thrown, and my ECU literally is running all those miles with trims over -10% but still not sure something is wrong!

Besides O2 sensors, what else have you checked/changed, and what are your fault codes and group 32 readings? MAF, vacuum leaks, clogged/cracked crankcase ventilation are the most common causes.

Cab_and_Wagons

Replaced the coolant temp sensor (also throwing a code), and fixed a small vacuum leak. The car is a 2002 allroad with the 2.7T. It runs and idles great, but throws 15745 and 17547. Long Term Fuel Trim Too Rich.

I looked at the OBD-II Freeze Frame data from the last code. Here's the result:

Freeze Frame Data for address 10
PID02 DTC that caused freeze frame data storage: P0175
PID03 Fuel system 1/2 status: Closed loop, using O2 sensors
... Closed loop, using O2 sensors
PID04 Calculated load value: 2.7 %
PID05 Engine coolant temperature: 87 °C
PID06 Short Term Trim - Bank 1: 2.3 %
PID07 Long Term Trim - Bank 1: 10.2 %
PID08 Short Term Trim - Bank 2: 2.3 %
PID09 Long Term Trim - Bank 2: 10.2 %
PID12 Engine RPM: 640 /min
PID13 Vehicle speed: 3 km/h

This was the log prior to replacing the O2 sensors.

cparke

The freeze frame and the DTC's you gave are very interesting to me...

First, the freeze frame is for DTC 16559/P0175, yet now you are getting 17545/P1137 and 17547/P1139. All of these codes nevertheless are System Too Rich, though I've never seen the 16559/P0175 and I'm not sure what the difference is between 16559/P0175 and 17547/P1139. Maybe your O2 sensor really did need to be changed.

MAF is another common culprit to check out.

BTW - do you still have the old O2 sensors?