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Premium Member
2003 325iT Titansilber
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8 Posts
Discussion Starter #1 (Edited)
Hello All,

I hate to be one of the many guys regarding this issue. But I've read what I believe is all that can be read in regards to this issue, and as part a PM over the past year have replaced old parts that I believe have been overdue to be replaced. I've replaced nearly everything that may have something to do with this, with the exception of my MAF sensor.

My car is a 2003 325iT.
Only major modification was that I converted it to manual.

My Issue:
P0171 and P0174 come and go as they please. On any cold start in the mornings there has not been any rough idle nor have I noticed the check engine come on due to these two codes. However, the moment I hop on and begin driving, eventually they will pop up, but then they go away, and pop up. One thing I did notice, they tend to like warm days, being as the warm days in SoCal are approaching, I wouldn't be surprised if they come around more often.

What I have done:
  • I did a smoke test and no leaks identified. I've done a smoke test multiple times within the past week.
  • Replaced the brake booster check valve last night, smoked it today, no leaks.
  • Replaced mostly every hose that has become brittle with new hoses.
  • Checked the rear of the intake manifold to make sure caps are on.
  • Replaced Camshaft Position Sensor 12147518628.
  • CCV replaced back in 2018, did the open oil cap test and pressure feels fine, no sign of it failing, no smoke.
  • Fuel pump and fuel filter within the past year (Bosch and Mahle).
  • Fuel pressure test stays at ~50psi and does not drop.
  • Fuel pressure retention test, drops 10 psi within 20 minutes of having reached 50 psi.
Logged 2 sets of data using OBD Fusion:
Set 1: Idle warm, don't know if it's closed loop (don't know how to determine open vs closed).
Idle Data
Set 2: Cruising warm.
Cruising Data

Any help will be appreciated.
 

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the people’s mod
2004 330Ci 115k miles
Joined
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15,067 Posts
Have you been through the @Archbid guide?
 

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Premium Member
2003 325iT Titansilber
Joined
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8 Posts
Discussion Starter #3 (Edited)
Have you been through the @Archbid guide?
I have not gone through this specific one. I’ve gone through jfoj’s thread/troubleshooting guide. And various of his responses to other members. Driving around right now, I finally was able to get some freeze frame data and only P0171 returned this time. I read through it and based on the procedure you linked I was leaning towards a faulty new fuel filter or pump. I’m taking my fuel injectors to get serviced over the weekend just due to the age of the vehicle and mileage (175k miles).
I’ve attached the freeze frame and I’ll keep digging at it. If you or anyone can help me understand a little more about what the freeze frame data can tell maybe. Thanks!
11891657-2D1C-46F5-9D9C-9C151635B462.png
 

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Registered
2000 E46 323i, 3.0L and 2.0L Z3's
Joined
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817 Posts
Had a look a your logs.

The MAF values had me really concerned until I realised that they were in some old imperial measurement. Set your OBD Fusion to record the MAF in g/s. That's what we use around here.

The MAF looks good. Hot idle value is right on the money and the highway run values look sensible for the load and driving you are doing. I do not think that the MAF is your problem.

The pre-cat O2 values are a different story. Bank 1 looks constrained and Bank 2 looks like it has a lean offset. You have 175,000 miles on the car. If they are the original sensors, then they are past their due by date for replacement (100,000 to 120,000 miles). Bosch are the preferred O2 sensors, get a set and see if that sorts your problems.
 

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Super Moderator
2003 330cic, 2003 325iT
Joined
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6,012 Posts
I would not clean the injectors. It is extremely unlikely they are the cause, and the money is better spent on O2 sensors (as @NZ00Z3 mentioned) which are definitely needed, and an intake refresh to seal off vacuum leaks.
 

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Premium Member
2003 325iT Titansilber
Joined
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8 Posts
Discussion Starter #6
Had a look a your logs.

The MAF values had me really concerned until I realised that they were in some old imperial measurement. Set your OBD Fusion to record the MAF in g/s. That's what we use around here.

The MAF looks good. Hot idle value is right on the money and the highway run values look sensible for the load and driving you are doing. I do not think that the MAF is your problem.

The pre-cat O2 values are a different story. Bank 1 looks constrained and Bank 2 looks like it has a lean offset. You have 175,000 miles on the car. If they are the original sensors, then they are past their due by date for replacement (100,000 to 120,000 miles). Bosch are the preferred O2 sensors, get a set and see if that sorts your problems.
Thanks for your reply. I can speak for bank 2 pre-cat o2 sensor, I replaced that one back in 2017, nearly ~64,000 km ago. As of yesterday I did order one to replace my bank 1 o2 sensor. I drove more today, P0174 decided to pay a visit. Possibly get the second for bank 2.
Changed my units from that ancient imperial method of measurement.
One thing I forgot to add. This morning during my cold start it struggled for about a second then started right up. No rough idle, but the P0171 did start soon after.
I’ll install the new O2 as soon as I get it.
Is there a book or thread somewhere that explains how to read the data? A few years back, reason for my changing the Bank 2 O2 sensor was me finding somewhere that explained what a lazy O2 looked like plotted, and that’s how I was able to diagnose my Bank to precat O2 sensor as being bad. I don’t recall the codes, that was back in 2017.
 

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Super Moderator
2003 330cic, 2003 325iT
Joined
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6,012 Posts
Thanks for your reply. I can speak for bank 2 pre-cat o2 sensor, I replaced that one back in 2017, nearly ~64,000 km ago. As of yesterday I did order one to replace my bank 1 o2 sensor. I drove more today, P0174 decided to pay a visit. Possibly get the second for bank 2.
Changed my units from that ancient imperial method of measurement.
One thing I forgot to add. This morning during my cold start it struggled for about a second then started right up. No rough idle, but the P0171 did start soon after.
I’ll install the new O2 as soon as I get it.
Is there a book or thread somewhere that explains how to read the data? A few years back, reason for my changing the Bank 2 O2 sensor was me finding somewhere that explained what a lazy O2 looked like plotted, and that’s how I was able to diagnose my Bank to precat O2 sensor as being bad. I don’t recall the codes, that was back in 2017.
Replace o2 sensors in pairs.
Take a look at the guide in my footer.
 

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Premium Member
2003 325iT Titansilber
Joined
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8 Posts
Discussion Starter #8
Replace o2 sensors in pairs.
Take a look at the guide in my footer.
Thanks, I took a look at all your guides earlier. I've been creating something similar for myself to track. Just been bad at logging it, I generally keep the receipts and write the mileage on the receipt. I've refreshed most of the mechanical items. This is my one and only problem right now.

I will replace in pairs, thanks for that note. I'll order the additional one.

Also, that OBD link you provided is how my OBD fusion is setup. I followed that years ago. I just have never been active til now. I'll record new data once these two have been replaced, only if they don't solve anything. Step forward to narrowing things down.
 

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Super Moderator
2003 330cic, 2003 325iT
Joined
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6,012 Posts
Different guide - I was referring to the one on P0171/4 and lean codes.

 

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Premium Member
2003 325iT Titansilber
Joined
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8 Posts
Discussion Starter #10
Different guide - I was referring to the one on P0171/4 and lean codes.

Alright, I ran through your thread. Began with fuel as you suggest. Here are the results of my tests on my fuel pressure.
Image #1 Fuel Pressure ~50> psi engine on
Image #2 Fuel Pressure dropped 1-2psi ~49psi
Image #3 Fuel Pressure dropped 4-5psi to about 44-45psi after 28mins

Photos are numbered on the bottom left corner.
I replaced fuel pump and fuel filter last year. I’m guessing one or the either is faulty? Or is this drop acceptable after 28 mins?

O2 sensors on the way.Eta Sunday.

05BAE5EB-7420-4D50-BEA5-EFB5BCD948B1.jpeg 2B97105A-0C2E-49BC-9F7B-9338E9F94112.jpeg 9090409B-FCE3-440C-8C48-353DBB01830B.jpeg
 

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Premium Member
2003 325iT Titansilber
Joined
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8 Posts
Discussion Starter #12
Was engine running or not?
Did you get 50psi instantly when you turned the key to position 2 (not running)?
Image 1. Engine was running, goal was to just measure my pressure. Read 50psi
Image 2. Engine not running, removed key, reinserted key, went to position 2, checked measurement. Read 49psi
Image 3. Engine not running, key off. Car left sitting for 28 minutes. Read 45psi
 

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Super Moderator
2003 330cic, 2003 325iT
Joined
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6,012 Posts
With a newish filter, I would expect it to hold pressure a little better, but It is within spec:

Fuel pressure 3.5 +/- 0.2 bar or 50.76 +/- 2.9 PSI
Residual fuel pressure after 20 minutes - Fuel pressure >3 bar or >43.51 PSI

Have you gotten the sensors yet?
 

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Premium Member
2003 325iT Titansilber
Joined
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8 Posts
Discussion Starter #14
With a newish filter, I would expect it to hold pressure a little better, but It is within spec:

Fuel pressure 3.5 +/- 0.2 bar or 50.76 +/- 2.9 PSI
Residual fuel pressure after 20 minutes - Fuel pressure >3 bar or >43.51 PSI

Have you gotten the sensors yet?
Thanks Archbid, I’m waiting on my second oxygen sensor. Also went ahead and just ordered a MAF sensor as part of PM since I’m already at 175k. I’ll post an update once I’ve cycled everything.
 
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Premium Member
2003 325iT Titansilber
Joined
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8 Posts
Discussion Starter #15
With a newish filter, I would expect it to hold pressure a little better, but It is within spec:

Fuel pressure 3.5 +/- 0.2 bar or 50.76 +/- 2.9 PSI
Residual fuel pressure after 20 minutes - Fuel pressure >3 bar or >43.51 PSI

Have you gotten the sensors yet?
Just as side note, prior to installing both oxygen sensors I cleared my Check Engine Light. I consisted of P0171, P0174, and P0313 which popped up yesterday after an hour long trip.

Installed the sensors, warmed up the car. I performed the tests in this order. Driving Warm, then, Idle Warm.
No check engine light on the Idle prior to beginning my drive.

Driving Warm:
On the drive to my destination I did not record data, on the drive back I did the check engine light came on with a P0171 and freeze frame data for the P0171, soon after P0174.
Freeze frame data attached below for P0171.
IMG_3946.PNG
CSV for Warm Drive data can be found here.

Idle Warm:
After ending my trip, just sat idling and recorded data for about 6 minutes.
CSV for Warm Idling data can be found here.

New MAF sensor not installed yet. Will be receiving Friday.

I appreciate all the help.
 

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Registered
2000 E46 323i, 3.0L and 2.0L Z3's
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817 Posts
Had a look at your logs after fitting new pre-cat O2's.
  • Pre-cat O2 values look a lot better
  • No real change in Total Fuel trims for either the hot idle or highway logs when compared to the previous logs. They are still terribly lean.
  • No real change in MAF values when compared to the previous logs. The Hot idle MAF value looks good. Highway log values look sensible.
  • The total Fuel trims get worse for the highway log compared to the hot idle log. This is not a vacuum leak. It is the classic symptoms for a fuel supply problem, but you have done, both the pump and filter with the right brand parts. That leave the MAF, which I see you have a new one on the way.

Could you please run the Rev Rise log for your car, both before you fit the new MAF and after you fit the MAF? Post the results in the normal way and I'll have a look at them. It will be interesting to see what difference there is in the results.

Rev Rise Test
  • Run your normal OBD Fusion log. Hot engine and Cat’s, stationary car. Slowly raise the rev's of the engine up from idle to around 3,000 rpm. I mean slowly. It should take you 3-4 minutes to do this test.
  • It takes some skill to do this test due to the lightly loaded engine. A little throttle change results in a large rev change. Don't run up and down the Rev range getting used to the control. If you stuff up the first part of the test getting used to controlling the small rev changes, then redo the test.
 
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