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2001 330i
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Discussion Starter · #1 ·
2001 330i with a 0 LTFT on bank 1, -3.9 on bank 2. Also giving the codes P0140, P0141 and P1155. At a bit of a loss, no idle fluctuation, no DISA rattle, fuel efficiency is completely normal.
 

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2001 330i
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Discussion Starter · #5 ·
How old are your post cat 02 sensors?
Not sure. I've owned the car for around a year and a half, P/O did a lot of work on it within the 2 years prior to me buying the car but I didn't see any mention O2 sensors.
 

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2001 330i
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Discussion Starter · #6 · (Edited)
Here's 2 OBD Fusion logs from this evening - one is a cold start with a 5 minute idle, the other is a 5 minute city drive. Feedback would be appreciated.

Cold start: Cold Start Data.xlsx

5 Min drive: 5 Min drive.xlsx

I'll also add in what maintenance I've done, all DIY with parts from FCP Euro:
Upper & Lower rad hoses
Expansion tank
Coolant flush
Water pump (went to a metal impeller)
Thermostat
Expansion tank bracket
Auto Trans thermostat
Coolant temp sensor
Valve cover gasket
Exhaust gaskets (cat to midpipe)

I have a lower intake boot but I haven't gotten around to replacing it yet due to the cold and that I don't have an indoor space to work on it.
 

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2000 E46 323i, 3.0L and 2.0L Z3's
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Look up the descriptions for your codes. You might want to list the descriptions in your post so that we all don't have to look them up.

Look at the post-cat O2 sensor data in your logs. Sensors that sit constantly at around 0.43V to 0.45V are not working.

Check:
  • Fuses
  • Connections
  • Wiring for burning
  • Change the sensors.
 

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2001 325i MT, 2001325i ZF auto,1999 328is auto
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56 Posts
Your pre-cat sensors seem to be taking too long to respond, they might be at fault.
In the cold start log, bank one never seems to reach a varrying voltage. Staying under a half a volt (slow responce) maybe dirty maybe old, like me.
 

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2000 E46 323i, 3.0L and 2.0L Z3's
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Yes, the cold start log did not run long enough to let the DME get into closed loop. So, we can't see the full pre-cat O2 sensor heating cycle. But the pre-cat O2 sensors were working OK in the drive log.
 

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2001 325i MT, 2001325i ZF auto,1999 328is auto
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56 Posts
I see you have done your Exhaust gaskets, Did you change bolts in the cats at the same time. Reason I ask, I cracked my bank 1 cat when removing the bolts from the cat. That gives funny readings, the post cat sensor varies its voltage rather than remaining stedy
 

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2001 330i
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Discussion Starter · #11 ·
I see you have done your Exhaust gaskets, Did you change bolts in the cats at the same time.
I did. 3 of the stock studs had been replaced at some point and the last remaining stud snapped during removal (exhaust dropped for a guibo/csb replacement). I ended up drilling out the remainder of the stud and replacing all of the bolts with stainless.
Yes, the cold start log did not run long enough to let the DME get into closed loop. So, we can't see the full pre-cat O2 sensor heating cycle. But the pre-cat O2 sensors were working OK in the drive log.
I can do another cold start log tomorrow, how long should I let it run?
 

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2000 E46 323i, 3.0L and 2.0L Z3's
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I can do another cold start log tomorrow, how long should I let it run?
Until you get to 1/2 operating temp of around 45C (100F). That is the needle on the temp gauge at just over the 1/4 mark. Being winter where you are, that may take a while.

It would also be good to see a hot idle log for a couple of minutes after a drive.
 

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2001 325i MT, 2001325i ZF auto,1999 328is auto
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When you did the Exhaust gaskets, did you replace the post cat o2 sensors? Best time to do this. The post cat sensors can be tough to get out without taking down the manifold, I tried many things.
Double check your post cat connections at the valve cover? Could be incompletely inserted! I did this. Look at the 50 kid utube video on taking manifolds down, It involves removing motor mount and jacking engine to lower front cat.
 

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2001 330i
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Discussion Starter · #14 ·
Here's a 5 minute warm idle from yesterday afternoon.


When you did the Exhaust gaskets, did you replace the post cat o2 sensors? Best time to do this. The post cat sensors can be tough to get out without taking down the manifold, I tried many things.
Double check your post cat connections at the valve cover? Could be incompletely inserted! I did this. Look at the 50 kid utube video on taking manifolds down, It involves removing motor mount and jacking engine to lower front cat.
I didn't, the main reason for dropping the exhaust was access to the driveshaft (CSB was completely torn apart) and for transmission mounts. I'll have to take a look at the connections on the valve cover tomorrow (got an ice storm where I live last night).
 

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2000 E46 323i, 3.0L and 2.0L Z3's
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I've run you warm idle and 5 minute drive log through my spread sheet. It's time I started sharing the spread sheets, so here you go, you're first up to have a look.

Warm Idle
  • MAF, RPM, Load all look OK. MAF is 10% over reporting at idle (causes rich fuel trims), but this is not bad enough to rush out and buy a new expensive MAF just yet. There are other things afoot that will take your money first.
  • Total Fuel Trims. Bank 1 is 10% to 15% lean (positive). Bank 2 is -1% to -9% rich (negative). There is a bank 1 only vacuum leak to find. There are not many parts that cause bank specific Lean trims. One is a failing pre-Cat sensor. The others are mostly vacuum leaks caused by recent work. Examples are:
    • Rolled or misplaced inlet manifold gasket
    • Leaking exhaust manifold gasket
    • Loose pre-cat O2 sensors. Yes, exhaust leaks before the pre-cat O2 sensors will cause lean trims.
  • Pre-Cat charts just confirm the fuel trims. There is no major offset between the pre-cat voltages.
  • Post-Cats. Your codes are all about the post cats. The voltages are flat lined at their biasing levels, so are not giving any signals. You do not have any O2 sensor heater failed codes, so the assumption is that the sensors are installed and connected.
5 minute Drive
The log we are after is a 2 to 3 minute highway cruise. Steady driving at around 100kmph (60mph). Using cruise control is best. Your 5 minute drive log does not have sufficient steady driving to do my normal analysis.
  • Total Fuel Trims, Speed. When ever your speed drops to zero, the Bank 1 total fuel trim jumps to 20% lean and the bank 2 jumps to about 5% lean. Otherwise, when driving, they are reacting to the accelerator and in the -5% to 5% range. Supports the bank 1 only vacuum leak.
  • Pre-Cat charts just confirm the fuel trims.
  • As before, Post-Cats have flat lined at their biasing voltages.

Overall Comments.
  • The Bank 1 LTFT is always zero. The STFT is doing all the mixture adjustment. Don't know what is going on, but it is not normal. The Bank 2 LTFT is adjusting as normal.
  • Smoke test the inlet manifold to see if you can find the bank 1 only vacuum leak. You'll need to be able to look for smoke under the inlet manifold, so get a mirror of camera in there.
  • You can also smoke test from the exhaust pipe back up to the exhaust manifold to check for exhaust leaks before the pre-Cat sensors. How to Smoke Test
  • The service life of the Pre-Cat O2 sensors are 120,000 miles. If yours are over due, you may like to change them.
  • Post-Cat voltages. Do you have cat-less headers? Have the post cat O2 sensors been fitted to anti-fouler's or similar extensions to move them out of the normal exhaust flow path? If not, then a new set of post-cat sensors will likely be needed.
Post-Cat O2 Voltages information
  • Cat's in good condition have Post-Cat O2 voltages above 0.5V when at steady highway cruise. There may be the odd momentary dips.
  • If O2 sensors are switching between 0.1 and 0.8V, then they are following the pre-cat O2 sensors (Cat’s not able to treat the exhaust) and indicates struggling Cat's. Expect to start seeing P0420 and P0430 codes.
  • If O2 sensors are flat lined somewhere below 0.5V, you have one of these problem:
    • Faulty post-cat sensors
    • Blocked Cats. Check fuel trims, they are likely double digit rich at this time.
    • Fuel mixture problems that are so lean that it is being reflected in the post-cat O2 sensor signals
Time invested
It's taken 2 hours to spread sheet your logs and write up this reply.
 

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Discussion Starter · #18 ·
Thank you for your time in doing this write up and analysis.

There are not many parts that cause bank specific Lean trims. One is a failing pre-Cat sensor.
Is there any way that I could check/test the sensor?

Do you have cat-less headers? Have the post cat O2 sensors been fitted to anti-fouler's or similar extensions to move them out of the normal exhaust flow path?
I do not, nor are there anti-fouler's installed, although that is something I will do if the cats are clogged.

I should have a chance to do a highway cruise tomorrow, so I'll have a look at that data and see if the post cats are below 0.5V. Would it be cats even if the fuel trims are still lean?

Once again thank you so much for the help.
 

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2000 E46 323i, 3.0L and 2.0L Z3's
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Is there any way that I could check/test the sensor?
The easy way is to unplug them, start the engine and see what codes pop up.
There could be lots of different codes. Some are:
  • Heater circuit codes
  • Sensor circuit codes
  • No sensor activity codes.
Plug them back in and see what clears. If the heater are working, then the sensor circuits are faulty. If no extra codes pop up, then suspect your DME. Maybe a firmware upgrade may solve it.

Also look at the list of things to check in post #7 above.

Would it be cats even if the fuel trims are still lean?
Blocked cats cause rich fuel trims under load. We are not seeing that in your fuel trims.
 

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Discussion Starter · #20 ·
It's been a few days, but I was finally able to do some sensor swapping and attempted diagnostics. Here's what I found:

With the sensors swapped (Bank 1 sensor plugged into Bank 2 harness and vice versa) the P0140, P0141, and P1155 were gone, but replaced with a pending P1137 and P0171.

With one unplugged, regardless of which was unplugged, just P1155 was shown.
 
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