P0171 P0174 Check Engine Light CEL - Page 5

racebmwm3 · #41 10-31-2023, 12:53 AM

STFT coming down into range while sitting here at idle after adaptation reset:

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80stech · #42 10-31-2023, 12:59 AM

Andrewwynn is again spouting a bunch of BS. The fuel pressure regulator line is vented to the intake boot on the E53 M54, not attached to manifold vacuum. At most it might compensate for a plugged air filter. If you had it attached to manifold vacuum it would drop your fuel pressure proportional to engine vacuum and cause your engine to run lean with the fuel trim trying to compensate

54-55 PSI engine/pump running sounds right to me but it's been a while so I might check again if I get a chance. It's pretty hard to get too much fuel pressure unless you put pressure on the regulator diaphragm.

racebmwm3 · #43 10-31-2023, 02:27 AM

Quote:

Originally Posted by 80stech

Andrewwynn is again spouting a bunch of BS. The fuel pressure regulator line is vented to the intake boot on the E53 M54, not attached to manifold vacuum. At most it might compensate for a plugged air filter. If you had it attached to manifold vacuum it would drop your fuel pressure proportional to engine vacuum and cause your engine to run lean with the fuel trim trying to compensate

54-55 PSI engine/pump running sounds right to me but it's been a while so I might check again if I get a chance. It's pretty hard to get too much fuel pressure unless you put pressure on the regulator diaphragm.

I get it.

So what do you think my issue is?

racebmwm3 · #44 10-31-2023, 02:59 AM

Update:

So after reseting my adaptations and starting the car up...

STFTs start high 15+
LTFTs at 0

During driving the car for 10-15 mins, the STFTs are slowly dropping (going up and down) in unison until they get around -8

At some point in time during this trip, the LTFTs went to 11.7.

(New) MAF sensor is < 3 g/s at idle (700RPM)

All during this trip, the O2 sensor output voltage on Bank 1 and 2 is looking proper - cycling between 0 and 1 volts - I have not seen this happen to date. Usually the voltage is pegged (lean) at 0 volts (or close to it).

80stech · #45 10-31-2023, 08:38 AM

The long term trim (block learn) is the one that matters, it's normal for the short term trim (integrator) to go up and down, if it can't keep up then it bumps the long term a notch and tries again. The o2 sensor should be cycling so that is good but if that is different after changing the MAF then you gotta wonder. The only way to really rule out the MAF is to replace it with a known good one. Puma is right about resetting the adaptations but in cases like this you can also just watch to see what changes starting from where you left off instead of re-setting and starting over. Also triple check the MAF connector as has been pointed out, they get yanked on a lot so you might have something going on there.

AND as has been pointed out CHECK FOR VACUUM/AIR LEAKS.

racebmwm3 · #46 10-31-2023, 09:40 AM

Quote:

Originally Posted by 80stech

The long term trim (block learn) is the one that matters, it's normal for the short term trim (integrator) to go up and down, if it can't keep up then it bumps the long term a notch and tries again. The o2 sensor should be cycling so that is good but if that is different after changing the MAF then you gotta wonder. The only way to really rule out the MAF is to replace it with a known good one. Puma is right about resetting the adaptations but in cases like this you can also just watch to see what changes starting from where you left off instead of re-setting and starting over. Also triple check the MAF connector as has been pointed out, they get yanked on a lot so you might have something going on there.

AND as has been pointed out CHECK FOR VACUUM/AIR LEAKS.

O2’s cycled to some extent before but would eventually peg lean before new MAF change.
Before resetting the adaptations and after replacing the MAF, I wasn’t getting better results so I reset the adaptations as a next step.
Can’t find any leaks anywhere. Smoked tested multiple times.
MAF wire seems fine. Manipulated it while watching data but couldn’t get any change to occur.

80stech · #47 10-31-2023, 11:25 AM

The most likely thing is still an air leak(s) somewhere. You say that it's expected that the engine runs rough with the oil cap off but it for sure is going to run rough if the CCV valve is shot so that isn't ruled out. I no longer have the CCV so I can't speak to what the crankcase vacuum should be if it is working correctly. With that many miles ( I have 450k kms) there is probably more than one thing going on as well. I know both my rear main seal and pan gasket are leaking air into the crankcase, my injectors are leaky, and my cats are probably not the greatest so I'm always on the edge of having the CEL come on/off. I can get my light out with engine oil stop leak, a can of cat cleaner, or boosting the fuel pressure a bit but none of that is consistent and that isn't really a fix.

If you haven't checked your fuel pressure driving under load you should do that as well.

racebmwm3 · #48 10-31-2023, 05:51 PM

Update:
Got a new fuel pressure test gauge. The new gauge is reading 49psi at idle. Still a little high per Bentley. Other sources I see online seem to think 49-50 psi is fine at idle.

With the new gauge, I did some more tests with the gauge attached to the fuel rail:

- Per @80stech, with the gauge secured on the windshield, I drove the car. The fuel pressure remained pretty constant at 49psi unless I blipped the throttle, which would cause the fuel pressure to drop a little bit temporarily.

- I removed the fuel pressure regulator "vacuum" line from the intake boot. The fuel pressure did NOT increase. Per Bentley, the fuel pressure is supposed to increase by 6-10 psi when doing this. It's not entirely clear but it seems as though Bentley wants you to remove the vacuum line AT the fuel filter. I removed the line at the intake boot, which I would think would produce the same result. Bentley says to replace the fuel filter/regulator if the pressure does not increase.

I have a fuel filter/regulator on order.

80stech · #49 10-31-2023, 06:09 PM

The regulator/fuel system doesn't work as it shows in the Bentley manual, BMW probably updated it and Bentley just carried forward the old info. It doesn't matter where you disconnect the vacuum line for the regulator it is not going to change the fuel pressure because the line is only being vented to the boot and isn't tied to engine vacuum. BMW likely decided not to use the vacuum portion of the regulator because the processors in the DME where getting fast enough to keep up without it. Some of the repair info didn't keep up though

racebmwm3 · #50 10-31-2023, 06:16 PM

Quote:

Originally Posted by 80stech

The regulator/fuel system doesn't work as it shows in the Bentley manual, BMW probably updated it and Bentley just carried forward the old info. It doesn't matter where you disconnect the vacuum line for the regulator it is not going to change the fuel pressure because the line is only being vented to the boot and isn't tied to engine vacuum. BMW likely decided not to use the vacuum portion of the regulator because the processors in the DME where getting fast enough to keep up without it. Some of the repair info didn't keep up though

I was wondering if this was an example of that. Very frustrating.

Well, I likely need a new fuel filter anyway, I don't recall the last time this was changed. I need to rule it out as well.

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