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      03-03-2020, 05:16 PM   #1
S_CDSM5
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Car running lean

So originally thought my stage 1 tune was causing my car to run lean but it appears its something else. Car has new spark plugs and was just at the BMW dealer getting a new passenger side fuel pump (bank 1) which they thought that solved the issue. The car is still pulling P0171 and P0174 codes. Sometimes its just one bank or sometimes it pulls codes for both. Any idea what it could be? Car drives relatively fine however it bucks quite a bit from a stop once i hit the gas, very jolty once i hit the gas. It does seem somewhat sluggish as well. Car also puts out a strong gas smell when im standing outside of it. Everytime i get out im like "damn this thing is stinky"... I was thinking possibly injectors? Anyone else with some insight? Car has 66k miles, bone stock besides charcoal delete and K&N filters.

Last edited by S_CDSM5; 03-03-2020 at 05:27 PM..
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      03-03-2020, 10:14 PM   #2
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The next thing I would look into would probably be injectors. Checked the MAFs at all?
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      03-04-2020, 04:35 AM   #3
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Quote:
Originally Posted by alpine_M5 View Post
So originally thought my stage 1 tune was causing my car to run lean but it appears its something else. Car has new spark plugs and was just at the BMW dealer getting a new passenger side fuel pump (bank 1) which they thought that solved the issue. The car is still pulling P0171 and P0174 codes. Sometimes its just one bank or sometimes it pulls codes for both. Any idea what it could be? Car drives relatively fine however it bucks quite a bit from a stop once i hit the gas, very jolty once i hit the gas. It does seem somewhat sluggish as well. Car also puts out a strong gas smell when im standing outside of it. Everytime i get out im like "damn this thing is stinky"... I was thinking possibly injectors? Anyone else with some insight? Car has 66k miles, bone stock besides charcoal delete and K&N filters.
I'd start with the cheapest and easiest thing first. Clean the mass air flow sensor with MAF cleaner from an auto parts store. Use YouTube as a reference on how to do the cleaning.
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      03-04-2020, 04:40 AM   #4
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Are the k&n's oiled?
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      03-04-2020, 09:25 AM   #5
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Quote:
Originally Posted by sumairm View Post
The next thing I would look into would probably be injectors. Checked the MAFs at all?
Have Checked the MAF and actually cleaned both. The K&N filters are oiled. I could try giving them a good cleaning again. Car is at the BMW dealership now, they agreed to diagnose for free. I am sure they will be able to get to the bottom of it. Sick of driving loaner cars, however in a 2020 M340 this time. Car is badass
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      03-04-2020, 12:59 PM   #6
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Turns out BMW is saying its the post cat o2 sensor on bank 2. no idea where that is
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      03-04-2020, 06:59 PM   #7
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Quote:
Originally Posted by alpine_M5 View Post
Turns out BMW is saying its the post cat o2 sensor on bank 2. no idea where that is
standing in front of the car bank 2 is drivers side.
remove the engine cover(black plastic with m5 badge on it) post cat would be the one I circled in pic [IMG]undefined[/IMG]


https://www.fcpeuro.com cheapest place I've seen. Will probably be listed as downstream o2
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      03-05-2020, 10:36 AM   #8
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Quote:
Originally Posted by RG604 View Post
standing in front of the car bank 2 is drivers side.
remove the engine cover(black plastic with m5 badge on it) post cat would be the one I circled in pic [IMG]undefined[/IMG]


https://www.fcpeuro.com cheapest place I've seen. Will probably be listed as downstream o2
Thanks man! i understand where it is. Quick question, do i need to have BMW reset the adaptation values for the CEL to not come back up? The tech was trying to tell me it cost $180 for them to do. I asked 3 other dealerships and they all said no, that is not true, just plug in the new one and clear the CEL and all good to go
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      03-05-2020, 10:58 AM   #9
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Quote:
Originally Posted by alpine_M5 View Post
Quote:
Originally Posted by RG604 View Post
standing in front of the car bank 2 is drivers side.
remove the engine cover(black plastic with m5 badge on it) post cat would be the one I circled in pic [IMG]undefined[/IMG]


https://www.fcpeuro.com cheapest place I've seen. Will probably be listed as downstream o2
Thanks man! i understand where it is. Quick question, do i need to have BMW reset the adaptation values for the CEL to not come back up? The tech was trying to tell me it cost $180 for them to do. I asked 3 other dealerships and they all said no, that is not true, just plug in the new one and clear the CEL and all good to go
just clear the code after install and you should be fine .
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      03-05-2020, 11:05 AM   #10
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Quote:
Originally Posted by RG604 View Post
just clear the code after install and you should be fine .
Cool thanks man!
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      03-08-2020, 07:36 AM   #11
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Really surprised a post cat O2 is causing those codes. I wouldn't be surprised if it doesn't fix the problem. Also, you really should replace them in pairs. (Do both banks at once). If you have 66k miles your precat O2's are due for change as well. I noticed an improvement in driveability when I changed mine at 65k miles.

If I was looking at the O2's as the source of lean codes, I would be changing the precat sensors first. Based on mileage, I'd be doing them anyway and killing 2 birds with one stone. Just my 2 cents.
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      03-08-2020, 01:24 PM   #12
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I agree with you. I thought it was weird the post o2 sensor was even going bad. Maybe pre but not post...maybe a bad catalytic converter? Wouldn’t think any of this would be happening at 66k. I had the car at one bmw dealership last week that said post o2 sensor and I just dropped the car off at another nearby bmw dealer to get a second opinion. If they say the same then I’ll replace the post o2 sensor and see. At this point I’m tired of dealing with this cars faults and issues and may trade it in on something simple like a 2020 M240 or something.
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      12-08-2020, 12:41 AM   #13
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Quote:
Originally Posted by S_CDSM5 View Post
I agree with you. I thought it was weird the post o2 sensor was even going bad. Maybe pre but not post...maybe a bad catalytic converter? Wouldn’t think any of this would be happening at 66k. I had the car at one bmw dealership last week that said post o2 sensor and I just dropped the car off at another nearby bmw dealer to get a second opinion. If they say the same then I’ll replace the post o2 sensor and see. At this point I’m tired of dealing with this cars faults and issues and may trade it in on something simple like a 2020 M240 or something.
Did replacing o2s ever solve your issue? I seem to be having the same problem with similar mileage. 68k throwing just the P0171 code
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      12-08-2020, 03:02 PM   #14
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Quote:
Originally Posted by glkmick View Post
Did replacing o2s ever solve your issue? I seem to be having the same problem with similar mileage. 68k throwing just the P0171 code
no was always something. getting rid of the car was the best thing i did
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      02-23-2023, 04:43 PM   #15
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Quote:
Originally Posted by glkmick View Post
Did replacing o2s ever solve your issue? I seem to be having the same problem with similar mileage. 68k throwing just the P0171 code

I got the same problem at 64k, did you manage to find what the problem was?
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      02-24-2023, 03:53 PM   #16
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Have you tried to revert back to stock / no tune. If you undo the tune and everything is fine, it could be the tune.

I know they replaced the fuel pump but depending on the tune you might need some new gear.

Have you tried reverting back and do you have the same issue.
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      02-26-2023, 05:55 AM   #17
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Quote:
Originally Posted by Stinkyxy View Post
Have you tried to revert back to stock / no tune. If you undo the tune and everything is fine, it could be the tune.

I know they replaced the fuel pump but depending on the tune you might need some new gear.

Have you tried reverting back and do you have the same issue.
I know this isn't a question for me but my car is completely stock and I got the same problem, I don't think its a tune issue.
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      02-26-2023, 08:58 AM   #18
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If you smell gas it's 9/10 a leaky injector.
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      02-27-2023, 06:40 PM   #19
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There is no fuel smell with mine. Just one bank showing negative and one bank positive. I guess the injectors could be going out but not enough to cause drivability issues now.
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