[NZ00Z3]

Looking at your logs now.

What fuel do you run in the car?

• Pure Gas
• E5
• E10

There is something odd going on and knowing the amount of ethanol in the fuel will help.

 

[NZ00Z3]

Sorry, I'm not in the USA so don't know the composition of the different fuels. I'll guess that it's E10.

 

[NZ00Z3]

Firstly, thank you for the excellent logs. Got them spot on first time out. Well done.

Here is my analysis file: 20221125 2004 330Ci Lean problems- Bluetech.xlsx

You might have multiple faults.

• A leaking bank 1 injector.
• A bank 2 exhaust leak before the pre-cat O2 or a loose pre-cat O2.
• A solf failing fuel pump or blocked fuel filter.

We'll start with Bank 1

Cold Start

• B1 Total fuel trim starts around -4% (rich). This is the last stored long term fuel trim. Running on E10, I would expect to see is around 5% (lean).
• Engine goes into closed loop control at around 50 seconds and both fuel trims follow a normal cold start trend B1 is slightly richer all the way through.
• Pre-cat O2 heating cycle is 0 to around 50 seconds. B2 follows the heating cycle perfectly. The SAP is dumping large amount of extra air into the exhaust making the exhaust very lean. B2 O2 sensor shows this. Now the B1 sensor is showing a rich mixture during this time. Either it's broken (but it's a new sensor) or the mixture is truly rich. Where would a 1 bank extra fuel supply come from? The only issues I can think of is a leaking B1 injector or a blocked Cat. It's really hard to get the E46 running rich. Either a leaking injector, blocked cat or a faulty sensor. The only Bank 1 specific sensor is the Pre-Cat O2 sensor. But it's a new O2 sensor.

Highway Cruise

• B1 Total fuel trims are cycling around -1% rich. In the days of pure Gas, this would be normal. But on E10 that should be cycling around 5% lean. B1 is still running rich.
• Pre-cat O2's. B1 O2 is showing sensible values.
• Post-Cat O2's. There is nothing to indicate a blocked Cat on either bank.

Hot Idle

• B1 total fuel trims are again rich, cycling around -2% rich
• Everything else has sensible values.

Bank 2

Cold Start

• Nothing unusual shows up in the cold start logs.

Highway Cruise

• The B2 total fuel trims are cycling around 10%. This is on the boundary for the P0174 code and why this code keeps coming up.
• All other charts show nothing unusual.

Hot Idle

• The B2 total fuel trims are all good, cycling around 2% lean.
• The noticeable thing between the cruise and hot idle logs is that the total fuel trims are worse at cruise than at idle. This is indicative of a soft failing fuel pump or a block fuel filter where it can't keep the fuel pressure/volume up to spec at cruise. Both the B1 and B2 fuel trims follow this trend.

Suggested next steps
Get a fuel pressure tester. One that fits the schrader valve on the fuel rail. Range is 51 PSI +/- 3 PSI

Check fuel pressure

• Key in position 2 with engine off.
• Engine running at hot idle
• Secure the gauge so you can see it and go for a drive to see if the pressure drops under load.
• Turn the key off and do a let down test for 20 minutes. It should not loose a significant amount of pressure, say 15 PSI. If it looses lots, and quickly, then you have a leaking injector.

Smoke test the exhaust to see if there are any exhaust leaks before the pre-cat O2's

Check that the pre-cat O2's are not loose.

Time Invested
It's taken 2 3/4 hours to spread sheet your logs and write up this post. I work for free, but it shows the level of work involved in looking at a set of logs. These one have been fun, they are not your normal issues.

 

[NZ00Z3]

Well, it looks like you have covered off all the normal repairs. I'll think some more.

One more item that will make one bank rich and the other lean is if the pre-cat O2's have been swapped. e.g. B1 plugged into B2's connector.

Can be checked by unplugging B1 while watching live data to confirm that B1 has stopped working.

 

[NZ00Z3]

One thing if somebody could look at there car and tell me which plug for the PRE O2 sensor is bank 1 and bank 2.

You are correct. The B1 sensor lead should not be able to reach the forward most connector. It appears to be the connectors that people swap.

The easy way to check, is to look at the O2 sensor live data. Unplug one and see if that is the sensor that stops working.

Another common issue, is that people do not clip the sensor leads back into the correct retainers. The leads flop about and melt on the hot headers.

 

[NZ00Z3]

Nope. The front O2 sensor is bank 1 (for cylinders 1-3), not bank 2.

This is always a good discussion point.

It depends on the engine wiring configuration/car model.

• If the pre-Cat O2 connectors are mounted on the side of the engine, just above the exhaust heat shields, then the front connector is for bank 1
• If the pre-cat O2 connectors are mounted under the engine top beauty cover, then the front connector is bank 2

 

[NZ00Z3]

Just curious does anybody have an idea which direction this issue might be going since the O2 sensor theory is ruled out?

It could be a bad MAF. Best checked with a Rev-Rise Log.

Rev Rise.

This test is for checking your Mass Air Flow Meter (MAF). Hot engine and Cat’s, stationary car. The test is best done just after a drive.

Slowly raise the Rev's of the engine up from idle to 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.

Post the log as per- before and I'll have a look.

 

[NZ00Z3]

Mixture codes can be broken down into:

• Vacuum leaks causing lean codes. Most common
• Failing Pre-Cat O2 sensors (rich or lean codes)
• Failing MAF (rich or lean codes)
• Exhaust leak before the pre-cat O2 sensor. Gasket or SAP problem. Causes lean codes
• Loose Pre-Cat O2 sensor, causes lean codes.
• Swapped pre-cat O2 connections. One bank goes lean and the other rich.
• Blocked Cat's. Can be lean at hot idle but rich under load.
• Performance coding of the DME causing rich or lean codes.

You've covered most of the bases with new parts already.

A quick mixture test
With a hot engine at idle, record the 4 fuel trims. If any are >8% then you likely have a vacuum leak.

Rev the engine to 3,000 rpm for 30 seconds and watch the short term fuel trims. If they drop significantly, might even go negative, then it is confirmed that you have a vacuum leak to find.

 

[NZ00Z3]

Let's look at the first part of the test

"With a hot engine at idle, record the 4 fuel trims. If any are >8% then you likely have a vacuum leak."

Your trims are all around zero, so there is no evidence of a vacuum leak.

The second half of the test where you rev the engine is therefore not needed. It does show that bank 1 long terms go rich with the short terms cancelling them out. Bank 2 is the opposite. Suggest you review post #6 and do the fuel pressure test to make sure you don't have a leaking injector.