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DIY: Do It Yourself
Post here to share or improve your wrench turning skills! All BMW E46 DIY tips, tales, and projects discussed inside. Learn to work on your car and know the right BMW parts you will need!

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Old 06-05-2015, 05:46 AM   #1
50sKid
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DIY - Most Common Vacuum Leaks (Diagnosing P0171 & P0174)

If you've got P0171 or P0174, you've got a vacuum leak and in this video I will go over all the most common causes for these leaks on the M54 & M52 engines. 95% of you who have this problem will be covered by this video. This is a great place to start if you've got this very common problem.



Hope you find it helpful.

-Jason
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Old 04-15-2016, 02:25 PM   #2
xtoor
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Hey man, i posted on your video, im the one with those codes.
I replaced:
-fuel pump
-fuel filter
-PCV System
-valve cover gasket
-disa
-upper intake boot was cracked
-cooling system thermostat and water pump included
-cleaned maf, icv, throttle body
-replaced dipstick tube o-ring

Still get rough idle loss of power on first 2-3 gears. Codes p0171 p0174.
Also i did mention smell of gas, i checked and there is no leak on filter and fuel pump or lines, however when i was removing the throttle body smell of gas escaped through the hole, its this normal or could it be an indicator of the problem? Fuel pressure its normal.

My Fuel trim on both banks are around %18, when i rev to over 3k rpm it drops momentarily, you said that it's not likely that both o2 sensor went bad but most likely a vacuum leak but at this point im lost no idea where to look next
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Old 04-16-2016, 06:52 AM   #3
markusmarkus
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Have the intake professionally smoke tested. Rose codes are classic indications of vacuum leaks.
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Old 04-16-2016, 05:43 PM   #4
50sKid
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Ok the behavior of your codes is clearly a vacuum leak, but it certainly sounds like you've taken care of all the obvious suspects. It is certainly theoretically possible to have bad o2s but if it were me I would be double checking my work, particularly on the ccv components. Have you taken a look at your o2 sensor live data? Are the precat o2s cycling rich/lean or are they pegged lean?
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Old 04-16-2016, 06:02 PM   #5
xtoor
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Lean like there is no tomorrow
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Old 04-16-2016, 06:05 PM   #6
50sKid
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Ok if your o2s (not fuel trim) are pegged lean, I would say you have good cause to replace them at this point.
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Old 04-16-2016, 06:07 PM   #7
xtoor
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I been also thinking manifold gasket, never been changed
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Old 04-18-2016, 09:54 AM   #8
xtoor
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See i did smoke test and no visible leaks found so i relly don't know whats up, then put in a bottle of seafoam and ran the trims see here what i get
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Old 04-21-2016, 04:07 PM   #9
xtoor
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During cold start MAF reads low and trims are 4.2 or so speak see here then after a few misfires and complete warm up MAF readings are way lower and trims go up see here i couldn't record all the time but after a good 20mins trims go back down to range 0 - 4 and MAF stay at low readings also noticed voltage on one of the o2 sensors is not reading on bank 1 bank 2 its 0.70 fluctuating
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