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  #1  
Old 10-19-2023, 11:24 AM
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P0171 P0174 Check Engine Light CEL

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
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Last edited by racebmwm3; 10-31-2023 at 05:27 PM.
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  #2  
Old 10-19-2023, 01:27 PM
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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%
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  #3  
Old 10-19-2023, 02:16 PM
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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.
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Old 10-20-2023, 08:29 AM
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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?
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Old 10-20-2023, 12:59 PM
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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.
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Old 10-20-2023, 01:40 PM
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Quote:
Originally Posted by andrewwynn View Post
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.
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Old 10-20-2023, 01:56 PM
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P0171 P0174 Check Engine Light CEL

The car runs rich when cold. I will also allow wider swings of fuel trim without an error.
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Old 10-21-2023, 12:19 AM
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Similar fuel trim problem, for over two years

I've been fighting my high fuel trims for two years, now, and have never found a vacuum leak (smoke tested 3x, carb cleaner test 4x, visual inspections as well).The O2 readings have always been good.

My fuel pressure tested barely 50psi, but only had two misfire errors over a year back, and none since (the engine starts and runs smooth as silk), so it's probably not the fuel supply. Rebuilt the DISA, replaced the filler cap & gasket (the only possible leaks I ever found), and I'm fairly sure the CCV is OK (23+ psi vacuum while running, according to Torque Pro, no sign of Mayo).

I cleaned my original Siemens MAF, and still had very high fuel trims, then tried a $20 MAF from Amazon, and the fuel trims got much better (the MAF readings were much higher), and that's the way I operate it now...having never completely eliminated the high trims. I also bought a second $20 MAF (Amazon owed me a refund on another purchase), and I now have three onboard. My conclusion, at that time, was that the Siemens MAF was underreporting, but there's got to be something else contributing to the lean condition.

I haven't driven my X5 since July, and only ran static tests in the driveway this summer, so when I had a Dr's appointment today, I put two bottles of Liqui Moly Jectron Fuel Injection Cleaner into the tank (previously filled in July), and took a chance on the state emissions test a few days early (due by 10-31), since I was out and about. It passed, despite LTFT's between 7-11, and the short terms trying to balance them.

I should've driven the X5 a few hundred highway miles with the cleaner in the tank, and the trims would've been better, I'm sure (my mpg goes up considerably, and the fuel trims go down as well, on the very few occasions where I give it the old Italian tune-up).

My new take on the lean condition is my injectors aren't flowing very freely. I have no idea how old they are, and/or their maintenance history. I have had good luck using Lucas Injector cleaner on my GM cars over the years, but I have no experience using Liqui Moly, but I'll find out. Now that it's getting cooler outside, I'll start driving and testing the X5 some more...I'm determined to find the root cause of the high fuel trims before the next inspection in October 2024. Maybe using some Cataclean is in my future, as well.
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Last edited by workingonit; 10-25-2023 at 06:51 PM.
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  #9  
Old 10-25-2023, 06:18 PM
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Update: bought a smoke machine.

Smoke tested:
Intake - no leaks
Vacuum booster - no leaks
Exhaust - no leaks

Then I drove it about 10 miles and was able to reproduce the lean condition.

This time however I noticed that bank 1 was lean while bank 2 was still looking ok.
Drove it some more and bank 2 started acting up again so both banks were now lean.

Drive it back home and did a smoke test while everything was good and hot.
Still no leaks anywhere.

Does the car go into closed loop one bank at a time?
If it goes to closed loop on both banks at once, sounds like it can’t be the fuel filter/regulator.

It may either be the fuel injectors or maybe the oxygen sensors.
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  #10  
Old 10-25-2023, 06:33 PM
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Quote:
Originally Posted by racebmwm3 View Post
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.
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