"System Too Lean" codes keep coming back..

[poch333]

Hello all, I'm really frustrated now. I've been reading through the threads here about these codes (P0171, P0174 -- System too lean, banks 1 and 2) and I've found a hole in the elbow as expected.

After fixing that, resetting, and doing the 15-mile drive cycle, it keeps coming back after a day or two. The scanner sees the "Pending DTC" code even before the CEL light comes on. I've gone through this process several times, putting RTV on the DISA, replacing cracking silicone hoses, cleaning the MAF etc and doing the drive cycle again.

Is there a way to determine whether the problem is a clogged fuel filter, broken MAF sensor, or fouled O2 sensors? Occasionally when cold it does seem to stumble during idle. I tried the "oil cap" test, and there was some suction and the engine stumbled but didn't die.

Also, will the CEL reset itself when the problem is fixed, or do I need to clear codes and do the drive cycle each time? To be honest I'm getting tired of driving 30 miles at 60 MPH late every night with my hazard lights on.

BTW, the Z3 has been parked for a few months prior to this, if it helps. I've also had to fix an EVAP leak.

Appreciate any inputs, thanks.

[328 Power 04]

You should get a smoke test done on the intake tract to find all the leaks. If there was one, chances are that there are many others. Most common cause is due to vacuum leaks. Sounds like your CCV is fine.

The code should be cleared manually when you fix the problem.

[Geo31]

This is a pretty common occurrence. There is a guy on E46Fanatics who has helped a lot of people with this. He starts by having people read this:

Solve your misfires, lean codes, rough idle - https://forum.e46fanatics.com/showthread.php?t=897616

Let me start out by saying I'm anything but an expert on these matters, but I've, ah, had some experience with them and others.

What are you using to read your codes? J recommends using an ELM327 (Bluetooth for Android products and WiFi for Apple products) and then the OBD Fusion app. He usually asks for a Freeze Frame dropped into Drop Box for him to read and then will make other recommendations, including doing a smoke test. Smoke testers can be made pretty cheaply with simple parts.

If you do not have OBD Fusion, I highly recommend it. I've used it multiple times on my Roadie, my E46, my wife's Tribeca, and a colleague's Odyssey. The last, I ended up saving my colleague a LOT of money. Without going into it, she and her husband don't have much disposable income at the moment. She was going to take her van to an indy to have it scanned. Instead, I came over on my lunch hour, read the codes. Cleared the codes. They came right back. A quick Google search and we found out it was covered under a recall campaign. Doubt the indy would have done that for her.

Based upon the age of our cars, and the repairs you have been doing, you probably really want to do a smoke test. While some of the things you mentioned are possible, they are all pretty much unlikely. The usual culprits are cracked and leaking gaskets and vacuum hoses. It's amazing the number of things that can throw those codes.

Oh, and while our cars are not E46, you undoubtedly have the same engine and set-up as an E46. Read the link to start with and we can go from there.

[poch333]

Hey thanks, George. I do have a reader that supposedly can capture freeze frames. I'm off to read that thread now.

328 Power: I was hoping I would not have to do the 15-mile drive cycle again after repairs but that's the way it is guess.

[Geo31]

I think the drive cycle is much longer than that. More like 50 miles.

I just put the Roadie back on the road after over 4 years. It definitely took more than 50 miles to be ready for testing, at least for Texas testing.

What reader do you have? I know J often requests live data as well.

[poch333]

Ar least for the O2 sensors, driving at 60 for 15 miles does the trick for me. The EVAP is the hardest, with a more complex cycle I haven’t figured out yet, but it has completed before with a few days’ normal driving.

I have the Nexpeak NX501 scanner, which claims to retrieve live data as well as freeze frames though I haven’t tried it yet.

Will take your advice to look for any remaining vacuum leaks.

[328 Power 04]

No, I meant you should use some kind of diagnostic tool to clear it yourself.

The drive cycle is for readiness, that's a different matter.

[poch333]

328 Power: Thanks, yes I understood. I just meant that after every repair I've had to clear the codes and perform the drive cycle in order for the O2 sensors to measure mixture again. And I really don't want to do it again after another fix.

[328 Power 04]

Your particular code is triggered from the learned long term adaptations, so it's not a drive cycle per se.

[bluptgm3]

328 Power: Thanks, yes I understood. I just meant that after every repair I've had to clear the codes and perform the drive cycle in order for the O2 sensors to measure mixture again.

Don’t need a drive cycle for O2 sensors to work again. They are always working until they don’t (and yes there can be degradation over time). It is the ECU that needs to ‘see’ the signal it is looking for, and the parameters within a working range repeatedly to set the ‘ready codes’.

How many miles on the O2 sensors? O2 sensors are known to have a ~100K life.



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[cleanerPA]

Evap codes require you to fill the gas tank beyond a certain point and a few drive cycles. I know this because I had an issue with my leak detection pump and it would go off nearly every time I filled the car with gas.

[poch333]

Don’t need a drive cycle for O2 sensors to work again. They are always working until they don’t (and yes there can be degradation over time). It is the ECU that needs to ‘see’ the signal it is looking for, and the parameters within a working range repeatedly to set the ‘ready codes’.

How many miles on the O2 sensors? O2 sensors are known to have a ~100K life.

It's at around 95k miles now.

[poch333]

Thanks to everyone who gave their advice, especially 328 Power 04 and Geo31.

The issue seems to be fixed. As you've suggested, the culprit was vacuum leaks and not O2 sensors, thankfully. I found them by making a DIY smoke tester using a glass jar, soldering iron, bicycle pump and some mineral oil. I followed this youtube video: https://www.youtube.com/watch?v=EhNQiIRsCCk

Before making the smoke machine, I used an OBD scanner to look at the Freeze Frame and Continuous Monitors, and was able to rule out bad O2 sensors or MAF. There's a video on youtube that describes how fuel trim works in general, and how to address lean issues specifically. I hope it can help out others in my situation. It was amazingly detailed and helpful: https://www.youtube.com/watch?v=5WnM_NsOtd8

After finding the leaks, I replaced hose clamps and RTV'ed some hoses. Cleared the CEL, went through the drive cycle and the lean codes did not come back. Again I was able to use the OBD scanner to compare the current data to the freeze frame data when the CEL occurred, and confirmed that the vacuum leaks were gone.

[Geo31]

Outstanding!

Sadly, I think I need to finally build my smoke machine. After a valve cover gasket change on my E46 I'm getting a persistent CEL. I've cleared it a couple of times and a couple of times it cleared itself. It's definitely transient, but still persistent. Boo hiss.

Thanks for posting the video about the fuel trim. I've been wanting to learn more about that.