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      01-11-2019, 05:48 PM   #1
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Short term and Long term fuel trims and Lean Codes...

Do these numbers look acceptable?



I have been getting SES light with lean codes for like 4 months. The codes are 29E0 and 29E1. I thought maybe a vacuum leak and have gone deep down the rabbit hole of fixing them but I have replaced the valve cover gasket, the valvetronic motor gasket twice, replaced intake manifold gaskets twice, gone over the whole intake tract. I even scrapped my old n54 manifold in case it was cracked/damaged and built another n54 manifold carefully and checked it over before install 3 weeks ago. Iím not seeing any evidence of a vacuum leak.

After all that still getting the codes typically at idle rpms, ~640rpms. Sometimes around ~3000 rpms though.

Iím thinking maybe there is still some sort of vacuum leak but maybe also something with the maf sensor.... Would a bad MAF sensor throw a code?

Also when Iíve googled these codes for n52 thereís isnít much that comes up but one thing Iíve noticed is that 3 of the other people on this forum who got these codes (out of less than 10 reported) all have the same AFE intake that I have:

Taskmaster
TheBigChill
Xencer

(So with me that makes 4 of us who have these same lean codes running the same AFE intake.)

And one has the Euro Airbox:

crazythedon

Did any of you guys find (or believe) your airbox was the issue?
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      01-12-2019, 01:27 AM   #2
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might want to try this. when i suspect a vacuum leak i put my hand to cover the throttle body. if there is no vacuum leak the engine shuts off. if there is a vacuum leak there will be a hissing noise then shut off. if its a large vacuum leak the engine will run rough with a loud hissing noise. the hissing noise is your leak. ive never tried this on a bmw but it worked well for me with other cars. hope it helps.

btw i have similar codes on bimmerlabs tune. i replaced both 02 sensors and followed the maf sensor write up on replacing the pin connectors. codes still persist. my car runs fine never really bothered to go in depth after that. but good luck.
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      01-12-2019, 07:44 AM   #3
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I did some reading last night and came across something helpful, maybe for others too.

ĒFor a suspected vacuum leak, note the fuel trims at idle and increase engine speed to 2500 RPM and hold. If the STFT immediately decreases and moves to acceptable levels and the LTFT slowly starts to come back down, you have a vacuum leak. After the repair, reset the KAM and start the vehicle. Monitor the fuel trims to make sure they are within the normal ranges. It could take up to 10 miles of driving for an accurate LTFT reading.Ē



I logged the fuel trims this morning and it did what that article said. They dropped considerably at 2500rpms to 14 and 16 from being 18 and 25 at idle. Fuel trims are only maxed at idle, and when I checked my logged codes they only trigger at idle rpms like 640. So that is pointing to a vacuum leak I guess.

At WOT 2500rpms they dropped way down to like 8.6 and 9.4.

I think the ecu trips the lean code when itís maxed the fuel trim and still canít get the mixture itís seeking. I remember reading that max fuel trim is 25%, so when the ecu hits 25% and still canít get the mixture to where it wants it trips the code.

In other words, if it could get the mixture to what it wants to see at a 24% correction I would never get a code.
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      01-12-2019, 10:23 AM   #4
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My car recently reported a lean code (P0174 -system too lean Bank 2). I also have the AFE intake. It was on the car for a while before I got the code. Other than this intake, my car is bone stock.

A buddy of mine who is a pretty sharp car guy plugged in his generic OBD II reader (he's a Volkswagen guy) and used an app on his phone to look at the engine parameters. He told me my fuel trims were high (+14%) and that it most likely due to the increased airflow from the AFE intake. I don't know if that was short term or long term fuel trim at 14%.

I checked all the clamped connections on the intact tract and everything looked tight. I pulled my MAF to see if it was dirty, and it looked spotless.

Since my car is still under extended warranty, I decided I would put the stock airbox back on and bring it to a shop. When I was taking the AFE intake off, I noticed that the foam gasket AFE supplies for the MAF had some grooving in it that MAY have caused a leak there.

I cleaned the MAF with the aerosol MAF cleaner, and installed the stock airbox. After about a week, the SES light went off on its own.

I ordered the Bimmergeeks cable and downloaded the BMW standard tools from Bimmergeeks. My plan is to use it to see if there are more specific BMW fault codes stored in the ECU.

If I don't get any additional information from INPA, I guess I may try putting the AFE intake back on with a new MAF gasket.
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      01-12-2019, 10:33 AM   #5
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Wurx thanks for responding. I found on my car after lean codes trip the SES light it will go off after a few ignition cycles even if I haven’t cleared the code. The codes are still stored and I can pull them and/or reset with my Carly. After reset the SES light will come on again when a new lean code occurs.

So just because you have not seen a SES light anymore doesn’t mean the issue is gone. You have to clear the codes and then have the light not come on any more to be free and clear.

Just so I can make sure I understand, did you reset the codes after swapping back to stock airbox and now they haven’t come back?

I’m thinking of swapping back to my stock airbox and clearing the codes to see what happens.
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      01-12-2019, 12:11 PM   #6
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Quote:
Originally Posted by Wurx View Post
My car recently reported a lean code (P0174 -system too lean Bank 2). I also have the AFE intake. It was on the car for a while before I got the code. Other than this intake, my car is bone stock.

A buddy of mine who is a pretty sharp car guy plugged in his generic OBD II reader (he's a Volkswagen guy) and used an app on his phone to look at the engine parameters. He told me my fuel trims were high (+14%) and that it most likely due to the increased airflow from the AFE intake. I don't know if that was short term or long term fuel trim at 14%.

I checked all the clamped connections on the intact tract and everything looked tight. I pulled my MAF to see if it was dirty, and it looked spotless.

Since my car is still under extended warranty, I decided I would put the stock airbox back on and bring it to a shop. When I was taking the AFE intake off, I noticed that the foam gasket AFE supplies for the MAF had some grooving in it that MAY have caused a leak there.

I cleaned the MAF with the aerosol MAF cleaner, and installed the stock airbox. After about a week, the SES light went off on its own.

I ordered the Bimmergeeks cable and downloaded the BMW standard tools from Bimmergeeks. My plan is to use it to see if there are more specific BMW fault codes stored in the ECU.

If I don't get any additional information from INPA, I guess I may try putting the AFE intake back on with a new MAF gasket.
the intake shouldn't matter.
it precedes the MAF sensor, so all air should be metered.

it's air that's introduced after the MAF that will cause you problems.
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      01-12-2019, 02:56 PM   #7
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I put my stock intake back on and took some measurements:

fallout pre war military

So with the stock intake on now I’m seeing a big change in the short term fuel trims. Like -25% at idle. This means the ecu is finding the engine running very rich at idle now and its and instantly cutting back on fuel. (25% reduction in fueling at idle seems a lot I never saw a negative number anything like that with the AFE intake.)

With the AFE intake the short term fuel trims were between 0 to positive 10% at idle, with AFE ECU felt the engine was running lean and was adding extra fuel.

So this may be premature but I think maybe the intake was the issue? I think the long term fuel trims will need to relearn over time now with the stock intake. As I see it now the ECU is significantly cutting fueling back on the short term trims at idle.

Also I noticed at idle the maf flow rates are different. I think maybe the AFE intake has a larger diameter maf area and more air gets by than with the stock MAF area.

If both those sample above were taken at the same rpms (they were) shouldn’t the maf flow rates be the same cause the engine is pulling the same amount of air on both samples? I think maybe a larger flow than the ecu believes goes into the engine with the AFE and then the ecu detects lean and adds a bunch of fuel.

Last edited by Biginboca; 01-12-2019 at 03:04 PM.
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      01-12-2019, 02:58 PM   #8
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Quote:
Originally Posted by nsjames View Post
the intake shouldn't matter.
it precedes the MAF sensor, so all air should be metered.

it's air that's introduced after the MAF that will cause you problems.
The AFE intake includes the MAF sensor and has a pipe that goes past the sensor to the throttle body. So it encompasses the oem MAF sensor and areas past it.

You install your oem maf sensor into the AFE intake pipe and I suspect it flows more than the stock intake (larger diameter?).
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      01-12-2019, 09:05 PM   #9
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I did not realize th AFE bit changed the MAF housing.

yeah, that may very well cause issue, as th MAF is calibrated for a certain diameter and housing.
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      01-13-2019, 10:01 AM   #10
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I found this great article on Fuel Trims and how they can correlate to diagnosing engine issues.

Going to post this here in case anyone is interested or find this thread in a search:

https://www.autoserviceprofessional....t-work-for-you
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      01-13-2019, 11:08 AM   #11
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Quote:
Originally Posted by Biginboca View Post
Wurx thanks for responding. I found on my car after lean codes trip the SES light it will go off after a few ignition cycles even if I havenít cleared the code. The codes are still stored and I can pull them and/or reset with my Carly. After reset the SES light will come on again when a new lean code occurs.

So just because you have not seen a SES light anymore doesnít mean the issue is gone. You have to clear the codes and then have the light not come on any more to be free and clear.

Just so I can make sure I understand, did you reset the codes after swapping back to stock airbox and now they havenít come back?

Iím thinking of swapping back to my stock airbox and clearing the codes to see what happens.

No, I never did clear/reset the SES light manually. When my buddy read the code for me, we didn't clear it.

The SES light went off on it's own after a few days driving with the stock airbox back on. That was a few days ago, and it hasn't come back on so far.

I find it odd that the AFE intake would throw a code like that. Seems like that would be well documented on the forums if that were the case. Or maybe less people have this intake on an N52 than I thought?

I would really like to put the AFE intake back on because when I took it off I really noticed how much more responsive it made the car feel. I don't know if it's power increase or just throttle response, but it made the care more fun to drive. I also really liked the induction sound it had.
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      01-13-2019, 02:35 PM   #12
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I think my issues lead to a fuel pump failure...
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      01-13-2019, 02:37 PM   #13
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Quote:
Originally Posted by nsjames View Post
I did not realize th AFE bit changed the MAF housing.

yeah, that may very well cause issue, as th MAF is calibrated for a certain diameter and housing.
I remember reading on the forum that the Bimmerlabs 330i tune does not use the MAF sensor. I'm thinking of using that tune when I install the 3 stage intake. Maybe it will allow the use of the AFE intake without getting a lean code if the intake pipe diameter difference is the issue. I don't know what the downsides are to not using the MAF sensor.
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      01-13-2019, 02:42 PM   #14
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Quote:
Originally Posted by Taskmaster View Post
I think my issues lead to a fuel pump failure...
Gotcha. Thanks for another lead. My gut feel was that the lean code is not just due to the AFE intake. I'll update this thread once I nail it down.
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      01-13-2019, 02:44 PM   #15
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Quote:
Originally Posted by Taskmaster View Post
I think my issues lead to a fuel pump failure...
So you don’t thing the AFE intake was related?

I learned something today from that article I linked... Fuel pump issue should be easy to diagnose based on what I have been reading. Failing fuel pumps have ever increasing fuel trims as RPMS rise.

At WOT the engine demands more and more fuel and comes short as demand on the pump increased, so the trims shoot up. It’s like the ECU is yelling at the pump “Scotty I need more power!” Lol
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      01-13-2019, 02:46 PM   #16
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Quote:
Originally Posted by Wurx View Post
I remember reading on the forum that the Bimmerlabs 330i tune does not use the MAF sensor. I'm thinking of using that tune when I install the 3 stage intake. Maybe it will allow the use of the AFE intake without getting a lean code if the intake pipe diameter difference is the issue. I don't know what the downsides are to not using the MAF sensor.
there is an option to use the tmap sensor like the euro intake had I guess.

mine is still using the stock MAF on the bimmerlabs 328>330 tune.

I assume that the tmap sensor is probably slightly less accurate, but I'm sure it's fine. We ran cars without maf sensors for a long while.
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      01-14-2019, 12:56 AM   #17
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There's no "tmap" sensor on the N52. There is a MAP sensor, and then there is the MAF/temp sensor. The euro cars mostly only use the temp sensor without a MAF. I haven't had a MAF on mine in a couple years now - I can't see going back.

That said, there are both MAF and no- MAF tunes available, so you have a choice. But these recent fuel trim threads are relevant, I just haven't had time to respond.
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      01-14-2019, 09:01 AM   #18
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Quote:
Originally Posted by hassmaschine View Post
There's no "tmap" sensor on the N52. There is a MAP sensor, and then there is the MAF/temp sensor. The euro cars mostly only use the temp sensor without a MAF. I haven't had a MAF on mine in a couple years now - I can't see going back.

That said, there are both MAF and no- MAF tunes available, so you have a choice. But these recent fuel trim threads are relevant, I just haven't had time to respond.
hassmaschine any chance you can expound on why you prefer a mafless tune?

Forgive my lack of knowledge, it seems to me like when you are getting into MILVís, headers, and now potentially exhaust cams the MAF tune would be easier to work with?
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      01-14-2019, 09:08 AM   #19
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To update this thread I have not had any lean codes since swapping my AFE intake back to stock airbox and after 3 day of driving my long term fuel trims have now fallen into much more sensible levels.

In all fairness the ambient temperatures have also not been as extreme as they were last week when I got the codes 3 times in a 24 hour period with the AFE intake.

We have a front coming through tonight so tomorrow morning will be the true test because the forecast is for the same temps as last week.
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      01-14-2019, 09:53 AM   #20
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Quote:
Originally Posted by Biginboca View Post
To update this thread I have not had any lean codes since swapping my AFE intake back to stock airbox and after 3 day of driving my long term fuel trims have now fallen into much more sensible levels.

In all fairness the ambient temperatures have also not been as extreme as they were last week when I got the codes 3 times in a 24 hour period with the AFE intake.

We have a front coming through tonight so tomorrow morning will be the true test because the forecast is for the same temps as last week.
Are you using the AFE supplied gasket on the intake? That's likely the biggest issue you're running into.
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      01-14-2019, 10:01 AM   #21
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Subbed.

have you done a smoke test on your system for leaks?
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      01-14-2019, 10:02 AM   #22
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Quote:
Originally Posted by Taskmaster View Post
Are you using the AFE supplied gasket on the intake? That's likely the biggest issue you're running into.
I’m on stock airbox now but with the AFE was using the foam ring they supply to go around the MAF sensor. Is that the gasket you mean?

The actual intake tract I had to make custom to line up with the n54 manifold. There are definitely no leaks in the intake tract I made from the MAF sensor to the throttle body.
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