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Old 04-16-2019, 09:17 AM
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Chasing P0172 and P0175 System too rich codes

I have been chasing 2 codes on the X5 P0172 and P0175 system too rich codes. I replaced the MAF with a new VDO unit from FCP Euro and both pre catalyst O2 sensors. Didn't have a single code for 8 months and now it's back.

My MAF seems to read high at idle at 4.7-4.8 g/s with all accessories off (A/C, radio, lights, etc) Can anyone let me know where their M54 MAF runs at warm idle?
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Old 04-16-2019, 09:34 AM
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I was having similar but opposite (lean), and I forced everything to reset by unplugging my O2 sensors for two starts. Just like you describe above, peace for 8 months then returns.

I have a feeling the parts in the DME that measure values are changing enough to register incorrectly.

What do your fuel trim values show and are your post cat sensors reading constant or bouncing around? I used non OEM pre cat sensors and suspect that is the source of my grief.
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Old 04-16-2019, 10:19 AM
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I reset adaptations with INPA and now at idle the long term fuel trims are at 0 and short terms were -14% cold and once warmed up the LTFT were still at 0 and STFT were around -2% and acceptable. I'm going to go drive around a bit and see if the trims LTFT change.

One thing I did not do when I replaced the MAF and O2 sensors was to reset adaptations but I assumed the DME would readjust? From my reading, everyone seems to point to resetting the adaptations is advised when changing type of fuel, air filters, O2 sensors or MAF. We will see I guess...
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Old 04-16-2019, 10:22 AM
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When I changed my front O2, I had immediate errors until I reset adaptations then no errors for months. I'm getting trim error post cat now (lean) just one bank but I don't trust my cheap pre cat sensors so those are getting changed soon.
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Old 04-16-2019, 10:34 AM
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When cold, O2 not used for fuel mix, so I'm thinking whatever long term adjustment due to wear etc are being used to estimate fuel mix and with new MAF it's sending a very different value. I'd definitely reset adaptations if you haven't already. I'm not sure if the same trick works on MAF as O2, but I had very good luck unplugging O2 to reset them wondering if the same will work on MAF.

Also rich when cold can be a flow restriction make sure you don't have an insect nest in your snorkel and that your air filter is clean
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Old 04-16-2019, 11:16 AM
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Quote:
Originally Posted by andrewwynn View Post
When cold, O2 not used for fuel mix, so I'm thinking whatever long term adjustment due to wear etc are being used to estimate fuel mix and with new MAF it's sending a very different value. I'd definitely reset adaptations if you haven't already. I'm not sure if the same trick works on MAF as O2, but I had very good luck unplugging O2 to reset them wondering if the same will work on MAF.

Also rich when cold can be a flow restriction make sure you don't have an insect nest in your snorkel and that your air filter is clean
Checked the air filter, it is looks new. Gar is garaged so no rodents have set up shop.

I took it back out for a 20 mile drive and LTFT are back to -8% but STFT are shoving back 8% to compensate. Something not right...
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Old 04-16-2019, 11:18 AM
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"the word on the street" is that ST opposite LT points to MAF. Do you have the original to put back for a control? Have you reset adaptations yet? If not I think the computer is basing a base calibration on the old MAF (educated guess).
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Old 04-16-2019, 11:24 AM
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Also: though opposite of the normal thinking that dirty injectors usually cause low flow = lean operation, they can also stick open and operate slowly to inject too much fuel. The other logical culprit is the FPR which is very rare failure but the computer absolutely depends on fuel pressure to be precise since it simply does math to determine how many miliseconds to measure how much fuel to inject. Pressure off 10% high you'll have 10% too much fuel until engine is hot and O2 can adjust.

I'd measure the fuel rail pressure. (sage advice I need to do the same myself as I'm getting constant lean codes).
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Old 04-16-2019, 10:53 PM
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If you replace components, your fuel trims will be whacky. What I mean by that is, say, you were running lean due to a vacuum leak. Your LTFTs might have been +10% (add fuel to balance the added air introduced due to the vacuum leak). You fix the vacuum leak but don't reset adaptations. Your STFTs will immediately go to -10% (offset the LTFTs based on having a vacuum leak that's now fixed). Gradually, your LTFTs will drop and move towards 0 while STFTs will slowly increase and move towards zero.

Not quite sure what your problem is, but I hope the above helps frame your troubleshooting.

I'd reset adaptations and observe the movement of STFTs at idle and then under load. If they're normal under load but negative at ilde, I'd say you have an idle air restriction.
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Old 04-17-2019, 09:48 AM
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I reset adaptations yesterday with INPA and at warm idle, LTFT was 0 and STFT was bouncing around -2.5%. I went for a 15 minute highway drive with some normal city traffic getting to the highway on each end. When I got back the LTFT was back to -8.1% and STFT shoving 7.5% back in.

At this point I thought possible fuel pressure so put a gauge on it and 54 PSI solid and dropping to 52 PSI when revving the **** out of it. So I am guessing the fuel pressure is within spec.

I also suspect a faulty VDO MAF although it is only 8 months old so I logged a steady state 3 or 4 minute run on the highway with cruise control set at 65 MPH. It appears the MAF follows the calculated load but I am still looking at data.
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Last edited by Overboost; 04-17-2019 at 12:47 PM.
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