P0171 P0174 Check Engine Light CEL

[racebmwm3]

INTRO:
Month ago I got a CEL for these codes ago. Reset the codes to see if they would come back.
They came back just recently so I added a bottle of Red Line S-1 to my full tank and drove it. The CEL came back on again after some time.
Now every time I reset the CEL light, it comes back on after 20 mins of driving.

DIAG:
Checked the intake boot etc for leaks, didn't find any.
Checked for leaks around the DISA (mine is fairly new) - none.
Checked for leaks around the intake gasket, didn't find any.
Checked for leaks at fuel filter, found a cracked vent hose. Replaced. Still throwing CEL.
CCV is fairly new, within last couple years.
Pulled oil cap, engine gets rough (as expected)

FUEL PRESSURE: ***
Fuel pressure at running idle - 55 psi (ABOVE max spec of 46.4)
Fuel pressure, jumped pump (car not running) - 54 psi (at max spec)
Fuel pressure drop after 20 mins shut down - 4 psi drop (within spec)

I got a lotta miles - 255k. Not sure I ever replaced the fuel filter. Might be the culprit. Do we agree? Or could there be something else causing the high fuel pressure? Or is this high fuel pressure in response to the lean condition?


***
10/31 - I got a new fuel pressure gauge: The new gauge is reading the following:

Fuel pressure at running idle - 49 psi (ABOVE max spec of 46.4)
Fuel pressure, jumped pump (car not running) - 49 psi

[racebmwm3]

SCANNER:

STFT B1 19.5%
STFT B2 21.1%

O2 B1S1 0.005v
O2 B1S2 0.94v

STFT B1S1 19.5%
STFT B1S2 99.2%

O2 B2S1 0.005v
O2 B2S2 0.935v

STFT B2S1 21.1%
STFT B2S2 99.2%

[Effduration]

Do you have the long-term fuel trims?

Your short-term trims are certainly quite high positive, but ST trims are often less informative..

Based on ST trims alone, I would suggest you have a proper smoke test, NOT one with a cigar and a fluid pump. The brake booster is one area folks miss when doing a smoke test..

your fuel pressure is 1-3 psi high, but I think that might be attributable to your tester.
Your fuel trims are positive which says the DME is adding fuel to the air/fuel ratio, So if it was over-fueling (and I have experienced this), The DME would reduce fuel to the mixture.

[racebmwm3]

Long term fuel trim bank 1 - 7.8%
Long term fuel trim bank 2 - 6.3%

Thanks for helping. Sounds like I need to purchase a proper smoke machine.

One thing I noticed is the numbers seem fine when the car first starts up but after driving like 20 mins and coming to a stop everything goes bad - o2 pegged lean and STFT skyrocket.

This is right after start up
https://share.icloud.com/photos/0dd5...FaRz4-19Fy6NcQ

Why would that happen?

[andrewwynn]

Smoke test but you can also use an unlit propane torch to spray near suspect areas while watching O₂ feedback real-time. BB is a giant diaphragm so can easily be a bug vacuum leak. You can pinch off the hose to test while watching O₂ or STFT.

Also; FPR uses vacuum hose for pressure reference to intake. You said that was replaced if that's plugged can cause fuel pressure problems.

Odd to see high fuel pressure and also high positive trims.

Can also be MAF sensor reporting wrong air value. The baseline calculation based on MAF the car adjusts fuel after the fact.

The error you're getting says there is unmetered air but it's the identical affect of MAF reporting inaccurate=low quantity.

[racebmwm3]

Originally Posted by andrewwynn

Smoke test but you can also use an unlit propane torch to spray near suspect areas while watching O₂ feedback real-time. BB is a giant diaphragm so can easily be a bug vacuum leak. You can pinch off the hose to test while watching O₂ or STFT.

Also; FPR uses vacuum hose for pressure reference to intake. You said that was replaced if that's plugged can cause fuel pressure problems.

Odd to see high fuel pressure and also high positive trims.

Can also be MAF sensor reporting wrong air value. The baseline calculation based on MAF the car adjusts fuel after the fact.

The error you're getting says there is unmetered air but it's the identical affect of MAF reporting inaccurate=low quantity.

I've tried spraying carb cleaner all over the place before and after the engine has heated up, but I have not observed a change in engine idle.

If it was the MAF, wouldn't it show lean right after start up? Mine is showing fine after start up, but pegs lean after 20 mins of warm up.

[JPuma]

Originally Posted by racebmwm3

I've tried spraying carb cleaner all over the place before and after the engine has heated up, but I have not observed a change in engine idle.

If it was the MAF, wouldn't it show lean right after start up? Mine is showing fine after start up, but pegs lean after 20 mins of warm up.

Do you have a tool to check your air flow. should be around 4.1-4.6g/s around 600 -700rpms.

[racebmwm3]

Originally Posted by JPuma

Do you have a tool to check your air flow. should be around 4.1-4.6g/s around 600 -700rpms.

I do. Keep in mind this is a x5 3.0...

It's around 3.5 @700 RPM

[andrewwynn]

Originally Posted by JPuma

Do you have a tool to check your air flow. should be around 4.1-4.6g/s around 600 -700rpms.

JPuma did the measurement and yep.

4.35 is the center of the range.

[JPuma]

Originally Posted by andrewwynn

JPuma did the measurement and yep.

4.35 is the center of the range.

This was a recent discovery for me. I had a bad maf wire for a long while. tried two MAF's to no avail. my problem was intermittent but didn't notice until I started monitoring airflow. Finally replaced the wire and its been stable since. I may have killed my Cat's because of this.