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BMW 325i 2001 Manual
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Discussion Starter #1
Hello all, I am a little stumped at the moment.

I have lean code P0174 after replacing my cats, I have done a smoke test and found 2 vac leaks which I resolved (the one-way valve for the break booster was leaking..), I don’t have any vacuum leaks anymore but I am still throwing the codes at 3200 RPM on a regular basis (once a day).

My car has the m56 valve cover with a new diaphragm and aluminium cap. Also, new O2’s and new catalytic converters (all replaced within the last 3 months). Fuel filter and pump are also “new” (replaced in the last 6 months).

The new cats are borla and not OEM, could they be the cause of these lean codes? If so, what could I do about it?

The car runs so smoothly and absolutely no hiccups or any sort of weird idle issues. No misfires at all.

The only thing I can think of is my injectors, that’s the only part of this car I haven’t touched/looked at yet.

Any advice would be appreciated please.
 

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The first thing to do is to start compiling some data logs of the car so you have something to troubleshoot. Folks here like ODB Fushion, so you might try that.

All sorts of things can cause lean codes on these cars, as I'm sure you already know. I'm not sure how well the aftermarket cats work, I installed used OE ones when mine went bad. But a bad cat will usually have other symptoms/codes associated with it, in my experience. Like bogging down, misfires under heavy load, fuel cutoff codes due to misfires, and etc.

Have you looked at/replaced the O2 sensors? Didn't see them on your list.

Could also be a clogged injector. You could send them out for cleaning. Could also replace their o-rings and swap them to the opposite banks.
 

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Discussion Starter #4
The first thing to do is to start compiling some data logs of the car so you have something to troubleshoot. Folks here like ODB Fushion, so you might try that.

All sorts of things can cause lean codes on these cars, as I'm sure you already know. I'm not sure how well the aftermarket cats work, I installed used OE ones when mine went bad. But a bad cat will usually have other symptoms/codes associated with it, in my experience. Like bogging down, misfires under heavy load, fuel cutoff codes due to misfires, and etc.

Have you looked at/replaced the O2 sensors? Didn't see them on your list.

Could also be a clogged injector. You could send them out for cleaning. Could also replace their o-rings and swap them to the opposite banks.
Thanks for the response! I don’t have OBDFusion, I do have bmw scanner and as you saw deepobd2. I will see if I can scavenge logs from those 2.

Yeah, my previous cats were causing misfires and fuel cut offs. Luckily those codes and issues are gone.

O2’s have been replaced for new ones about 3 or 4 months ago. Bosch.

I am a little weary about touching the injectors, never done that on a bmw before, is there a way to diy clean them or is it a really specialized job?

Swapping the banks is a good idea! I think that’s going to be my next step. I would like to try clean them myself and swap the banks. I’ll see if I can find any good tutorials on cleaning on here.

Thanks again DaHammer!
 

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I wouldn't try to clean them myself, but you could try a few tanks of Techron injector cleaner in them. Getting them out isn't a hard job, just a little time consuming. I'd at least replace the O-rings, if you take them out. But you'd probably better off to just send them to someone like WitchHunter and have them cleaned professionally.

One issue I had when I removed mine was that the schrader valve on the fuel rail leaked afterwards. BMW doesn't sell just the valve, but I found an AC Delco one that worked great thanks to someone's post on the board.

Lots of videos on removing them on Youtube. See 50skid's intake removal videos for one.
 

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Discussion Starter #6
I wouldn't try to clean them myself, but you could try a few tanks of Techron injector cleaner in them. Getting them out isn't a hard job, just a little time consuming. I'd at least replace the O-rings, if you take them out. But you'd probably better off to just send them to someone like WitchHunter and have them cleaned professionally.

One issue I had when I removed mine was that the schrader valve on the fuel rail leaked afterwards. BMW doesn't sell just the valve, but I found an AC Delco one that worked great thanks to someone's post on the board.

Lots of videos on removing them on Youtube. See 50skid's intake removal videos for one.
Good to know, I actually found the 50sKid video on cleaning the injectors... seems like I will be sending them to get professionally cleaned haha.

I will get the o-rings when I swap the banks out. In the same video he explains very clearly how to troubleshoot whether it is fuel delivery or vacuum leak. I am sure it’s not a vacuum leak, but it’s always good to cover all basis.

My first step now, would be to check fuel trims at idle and at 3k rpm. And correlate all the info etc. will post results as soon as it’s done (probably this coming Saturday).
 

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2004 330Ci 85k miles
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I would hold off cleaning the injectors for now, they are rarely the issue on vacuum leaks.

Get a wireless OBD adapter and OBD Fusion app on your smartphone or tablet. Hit the link in my sig,
Then do a Diagnostic Report at hot idle, so we can see the trouble codes, freeze frame data, fuel trims, MAF value, etc. Post a link to that Diag Report here.
 

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Discussion Starter #8
I would hold off cleaning the injectors for now, they are rarely the issue on vacuum leaks.

Get a wireless OBD adapter and OBD Fusion app on your smartphone or tablet. Hit the link in my sig,
Then do a Diagnostic Report at hot idle, so we can see the trouble codes, freeze frame data, fuel trims, MAF value, etc. Post a link to that Diag Report here.
Could I use bmw scanner instead? Probably not, but it would be nice, because then I don’t have to wait for the adapter to get to me, I have a Bluetooth one which doesn’t work with obd fusion.

Thanks!
 

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Could I use bmw scanner instead? Probably not, but it would be nice, because then I don’t have to wait for the adapter to get to me, I have a Bluetooth one which doesn’t work with obd fusion.

Thanks!
BMW Scanner 1.4 is poor for diagnosing engine running issues.
It does show live data for MS43 DME, which you seem to have, so check that.

I did not see your year and model E46 mentioned.
 

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Discussion Starter #10
BMW Scanner 1.4 is poor for diagnosing engine running issues.
It does show live data for MS43 DME, which you seem to have, so check that.

I did not see your year and model E46 mentioned.
My apologies, it is the MS43, 2001 325i. Manual swapped.

If it’s not good, I will just wait for the obd scanner. I am hoping the foseal I got will suffice.
 

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Discussion Starter #11
Okay, got all the obd fusion stuff configured to what the PDF outlined, I have the cold start sheets + cold start diag report. I will be taking a warm idle later today.

I would also like to add that the issue only happens at 3200 RPM (or at least that’s when it’s reported), so I am starting to believe that I do indeed still have a vac leak, but I cannot find it with a smoke test. Which is frustrating.
 

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Discussion Starter #12
Okay, here are my logs: Warm and cold. Do not have a highway run yet. If needed I can provide it. The "Random" folder contains my run around the block to warm the car up. (Sorry its not dropbox. Hope Google Drive is okay).

Side note, apparently I would fail emissions testing... I am confused as to why the O2's are reporting they are not heated, but they are...
 

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Discussion Starter #13
Oh, it’s a BMW 325i, m54, ms43 DME, with a m56 valve cover conversion. It has been converted to a manual. Mileage is 208,xxx miles. New CATs, O2’s, fuel pump and filter (in the last 4K miles), new coil packs (in the last 5k miles) and the spark plugs were replaced about 10k miles ago.

All the work has been done by me. So it’s entirely possible that I overlooked something. Also, no oil leaks as I changed almost all gaskets/seals on the motor (only one not changed is the crank seal).

Smoke test has been done (I lost count after the 5th one) all in the span of a day, while chasing the vac leak last weekend Saturday.
 

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2003 330cic, 2003 325iT
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First off, I am not exactly sure what is triggering the P0171/4. Your fuel trims are slightly above +/- 3.0 spec, but well under the threshold for that code. This suggests that you have likely dealt with the leak and fuel delivery.

The MAF readings are low, and at 208k, if you are on your original MAF, it really should be replaced. VDO/Siemens only, but I believe that FCP now sells the cheaper Hyundai one (same mfg).

MAF doesn't just fail, it under-reports, leaning out the mixture (from the ECU's perspective) and causing the ECU to adjust the trims incorrectly.

BTW, nice work on maintenance!
 

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Discussion Starter #15 (Edited)
First off, I am not exactly sure what is triggering the P0171/4. Your fuel trims are slightly above +/- 3.0 spec, but well under the threshold for that code. This suggests that you have likely dealt with the leak and fuel delivery.

The MAF readings are low, and at 208k, if you are on your original MAF, it really should be replaced. VDO/Siemens only, but I believe that FCP now sells the cheaper Hyundai one (same mfg).

MAF doesn't just fail, it under-reports, leaning out the mixture (from the ECU's perspective) and causing the ECU to adjust the trims incorrectly.

BTW, nice work on maintenance!
YES!!!! That’s what I needed to hear!!! Okay, so I am not crazy...

I checked the trims and they seemed fine, but this is my first bmw and I wasn’t too sure about it.

I believe it is the original MAF, I am ordering one today.

Thanks for the compliment, next on the list is a power steering refresh, I just ordered all of the hoses + tank :) it’s been a very long year of a lot of maintenance every weekend and every vacation day. Finally I am seeing improvements and performance being close to what it came out of factory! Love it.

EDIT: FCP seems to only have the VDO MAF, looking on amazon for quicker delivery. Noted about the Siemens/VDO only, sensors have to always be OE/OEM in my eyes.

EDIT2: found this on amazon, ships a lot quicker than FCP, so I want to use this: BMW Mass Air Flow Sensor MAF Siemens VDO OEM 5WK96050Z / 13621432356 Amazon.com: BMW Mass Air Flow Sensor MAF Siemens VDO OEM 5WK96050Z / 13621432356: Automotive

According to realOEM, it’s the correct part. Pins also look correct. So I will be ordering this, unless anyone thinks I should not? (B2C auto parts is the shop, I like them, I have purchased from there before, my whole cooling system refresh came from them, all OE parts).
 

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YES!!!! That’s what I needed to hear!!! Okay, so I am not crazy...

I checked the trims and they seemed fine, but this is my first bmw and I wasn’t too sure about it.

I believe it is the original MAF, I am ordering one today.

Thanks for the compliment, next on the list is a power steering refresh, I just ordered all of the hoses + tank :) it’s been a very long year of a lot of maintenance every weekend and every vacation day. Finally I am seeing improvements and performance being close to what it came out of factory! Love it.

EDIT: FCP seems to only have the VDO MAF, looking on amazon for quicker delivery. Noted about the Siemens/VDO only, sensors have to always be OE/OEM in my eyes.

EDIT2: found this on amazon, ships a lot quicker than FCP, so I want to use this: BMW Mass Air Flow Sensor MAF Siemens VDO OEM 5WK96050Z / 13621432356 Amazon.com: BMW Mass Air Flow Sensor MAF Siemens VDO OEM 5WK96050Z / 13621432356: Automotive

According to realOEM, it’s the correct part. Pins also look correct. So I will be ordering this, unless anyone thinks I should not? (B2C auto parts is the shop, I like them, I have purchased from there before, my whole cooling system refresh came from them, all OE parts).
The Hyundai MAF is the VDO/Siemens MAF. They provide for both carmakers - 13621432356 is correct. Get it from FCP, for one because we need to support people who dedicate themselves to our platforms, and second because they have a lifetime guarantee.
 

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Discussion Starter #17 (Edited)
The Hyundai MAF is the VDO/Siemens MAF. They provide for both carmakers - 13621432356 is correct. Get it from FCP, for one because we need to support people who dedicate themselves to our platforms, and second because they have a lifetime guarantee.
I agree with that but the same part is $20 more on FCP along with taking a week longer to deliver.. usually it’s quicker on FCP so I get it from them. But waiting 3 weeks for a small part is a little bit of a stretch.

To get it at the same time frame as B2C, I would need to add 28$ for delivery, so that works out to 48$ more for the same thing.

Or do you think I should just wait 3 weeks to get it and call it a day? Since I am supporting a different shop that dedicate themselves to our platform. At a better rate, competitive prices = better pricing for us, no? : P

EDIT: not trying to sound sarcastic or rude, I am being genuine about the question. And I am curious to see if that seems fair or not.
 

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Three weeks to get it from fcpeuro sounds rather long.
I live on the other side of the country from fcpeuro, in SoCal, and usually get delivery in less than 1 week using the (slow) free shipping option.
 

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Discussion Starter #19
Three weeks to get it from fcpeuro sounds rather long.
I live on the other side of the country from fcpeuro, in SoCal, and usually get delivery in less than 1 week using the (slow) free shipping option.
Usually to me too, I’m not sure what’s going on at the moment...
 
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