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Old 09-09-2016, 11:14 AM   #1
IcyMoustache
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P0171/4/Lean codes - Dont overlook MAF diagnosis

TL;DR:

1. If you are having lean codes, first and foremost diagnose MAF. This before jumping into smoke tests and the ensuing rabbit hole.
2. Diagnosing MAF is very easy if you have OBDfusion or equivalent
3. Delphi MAF works just fine (cant evaluate durability yet)

Detail:
I finally got around to get my car pass inspection. I raised the issue several months ago:
http://forum.e46fanatics.com/showthread.php?t=1100706

Where dslboomer's post intrigued me:
Quote:
Originally Posted by dslboomer View Post
I doubt vacuum leak is the cause of P0171 & P0174 if smoke test could not find sizable leak.

How do you know MAF was not a cause from OBDfusion?
You should know by now to post freeze frames and logs for your problem.
Let me see your log at warm idle.
Couldnt get around to really looking into it till recently (too much travel). Did a volumetric efficiency analysis based on MAF lb/sec reading. Analysis similar to http://forum.e46fanatics.com/showthread.php?t=617788. Noticed a volumetric efficiency of 40%, much lower than expected >75%. Replaced the MAF with a Delphi AF10022 and everything just fell in place.

In retrospect, I should have done this before the countless hours spent agonizing, reading forums, doing smoke tests, and replacing a bunch of parts. Lesson learnt. So passing the message around. (As jfoj repeats so many times) Please diagnose through OBD readings before doing smoke tests before actually replacing parts.
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Old 09-09-2016, 12:14 PM   #2
All2kool
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I'm fairly certain my MAF was causing my P0171/0174 codes as well. I replaced it with a budget one from EBay and haven't seen a code since. I also replaced both Intake Boots and the O-Ring on the DISA. It's been 200 miles and I have no codes and none pending. It' was the best $18.35 I ever spent.

If your MAF still has a white sticker on it, it's likely the one the car left Germany with. After more than 100,000 miles, it's easy to accept that it can no longer accurately read Air Flow.

Last edited by All2kool; 09-09-2016 at 12:23 PM.
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Old 09-10-2016, 04:05 AM   #3
Landlorder
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Interesting. Ebay maf fixed your issue. Let us know how long it lasts.


Quote:
Originally Posted by All2kool View Post
I'm fairly certain my MAF was causing my P0171/0174 codes as well. I replaced it with a budget one from EBay and haven't seen a code since. I also replaced both Intake Boots and the O-Ring on the DISA. It's been 200 miles and I have no codes and none pending. It' was the best $18.35 I ever spent.

If your MAF still has a white sticker on it, it's likely the one the car left Germany with. After more than 100,000 miles, it's easy to accept that it can no longer accurately read Air Flow.
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Old 09-10-2016, 09:21 AM   #4
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Quote:
Originally Posted by Landlorder View Post
Interesting. Ebay maf fixed your issue. Let us know how long it lasts.
I read the reviews for the seller before making the huge investment of $18.35. He had sold many MAF's and not one buyer had a complaint.
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Old 09-10-2016, 11:12 AM   #5
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There is no way an $18 MAF is any good. Even most used MAF's are probably questionable, but people would be charging $50-$75 for them.

Measuring airflow is a very precise and difficult task. One reason MAF's are expensive is they have Platinum in them. Look up the price of Platinum and you will get an idea as to why they are expensive.

There are MANY, MANY Asian counterfeit MAF's on the market. They may seem to work well at idle, but the airflow measurements are garbage under all other conditions.

Anyone that feels they need to spend so little on maintaining their personal vehicle should really consider a bicycle.

For anyone that is reading this thread and thinks an extremely cheap MAF from ebay will solve your problems, think again, it won't. I do not care what anyone has to say, it is not going to happen.

Diagnosing fuel system management problems is not so difficult. But anyone that wants and expects quality assistance needs to start with OBDII codes, Freeze Frame and Fuel Trim data. Logs are very helpful as well. Without this information, everyone is chasing ghosts.

Anyway, for anyone that thinks their car is running properly with a $18 ebay MAF, good for you, but you obviously do not understand how modern fuel systems are managed, what sensors are critical and why many sensors are so expensive.

I certainly would never recommend a $18 ebay MAF. Hell even the SAP MAF on the newer cars is at a best price of around $75 last time I checked. This is a much smaller and simpler MAF that measures the amount of air the SAP uses.

Do not get your hopes up!
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temp, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose temp switch O-ring - BMW #13621743299
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Old 09-10-2016, 11:21 AM   #6
All2kool
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Quote:
Originally Posted by jfoj View Post
There is no way an $18 MAF is any good.
So what brand of MAF is it that you manufacture then?

If my car starts throwing codes again, I'll let you know. I would put the old MAF back on just for giggles but why? I've got 200 miles on this one and I am code free. Did I have a leaky or not fully seated Lower Boot? Can't say, I never did a smoke test. What I do know is that after reseating the new Lower Intake and replacing the DISA O-Ring and installing my 'no good' MAF, my lean codes disappeared.
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Old 09-10-2016, 02:27 PM   #7
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There is no reasoning with you and you clearly do not, nore want to, understand how fuel system management systems work.

Again, you do not understand I am not trying or wanting to help you out, we have been down this path before.

I am trying to help people that may read this thread from making the same mistakes you seem you choose to make.

There is no such thing as a $18 MAF that correctly and properly measures air flow and air density. It is not going to happen.

But as long as you are happy and think your car is fixed is all that counts.
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temp, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose temp switch O-ring - BMW #13621743299
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Old 09-10-2016, 03:20 PM   #8
All2kool
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Quote:
Originally Posted by jfoj View Post
There is no such thing as a $18 MAF that correctly and properly measures air flow and air density. It is not going to happen.
Yet hundreds and hundreds of buyers find otherwise.
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Old 09-10-2016, 03:41 PM   #9
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And some people believe in the Tooth Fairy and Free Lunch.

I am not worried about you, I am worried about anyone that reads this thread in the future and I am trying to guide them in the correct direction to not waste money and properly repair their vehicle.
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temp, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose temp switch O-ring - BMW #13621743299
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Old 09-10-2016, 04:12 PM   #10
All2kool
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If you had read my post carefully you would have seen 'I'm fairly certain my MAF was causing my P0171/0174 codes'. My post also indicated that I changed the O-Ring on the DISA and replaced the Lower Intake Boot. I never said that I was positive that it was my MAF and I clearly detailed all of the steps I took.

Your attitude of always knowing what is good and what is not is disturbing. I hope that other forum users here don't blindly accept what you post as you could be sending people down the primrose path that does not lead to a solution. I shared what I did in the hopes that others could learn from it.

Last edited by All2kool; 09-10-2016 at 04:55 PM.
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Old 09-10-2016, 06:14 PM   #11
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All2kool please tell us your long term fuel trims with this ebay maf. Im with jfoj on this.
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Old 09-10-2016, 07:39 PM   #12
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My lean codes eventually led me to replace my maf sensor as well.

Countless times I kept doing all sorts of smoke tests.. Until I finally said fvck it and bought one since it was rhe only item not replaced.
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Old 09-10-2016, 08:07 PM   #13
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Quote:
Originally Posted by Landlorder View Post
All2kool please tell us your long term fuel trims with this ebay maf. Im with jfoj on this.
Just the moment I get a code or one pending, I'll let you know.
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Old 09-10-2016, 08:25 PM   #14
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temp, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose temp switch O-ring - BMW #13621743299
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Old 09-10-2016, 08:38 PM   #15
IcyMoustache
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@tks

It is so easy to overlook, especially given potential cost of replacement ($300), the uselessness of typical MAF cleaner spray advice, and the overabundance of wrong diagnoses on internet.

e.g. one diagnosis that keeps coming up is the "unplug MAF" based diagnosis. While it is fine, it doesnt diagnose the soft failure of MAF (when it slowly deviates in reported reading).

The sad part is how easy the real diagnosis is. The reason the real diagnosis didnt really take off is because experts in this forum keep asking for fuel trims and logs at warm idles. By this they are giving people a fish. Rather it would be good to just teach people to fish... In other words whats really missing is a clear DIY on how to use OBD for complete diagnosis. i.e. here are the complete set of PIDs to measure in OBD or PA Soft, here are the analyses we could do, and here is what the analyses point towards. A structured issue/diagnosis tree.

Last edited by IcyMoustache; 09-10-2016 at 08:44 PM.
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Old 09-10-2016, 09:00 PM   #16
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Quote:
Originally Posted by IcyMoustache View Post
The sad part is how easy the real diagnosis is. The reason the real diagnosis didnt really take off is because experts in this forum keep asking for fuel trims and logs at warm idles.

By this they are giving people a fish. Rather it would be good to just teach people to fish... In other words whats really missing is a clear DIY on how to use OBD for complete diagnosis. i.e. here are the complete set of PIDs to measure in OBD or PA Soft, here are the analyses we could do, and here is what the analyses point towards. A structured issue/diagnosis tree.
I guess you are referring to me?

Again, there is a LOT more to all of this most people realize. Unfortunately there is no specific trouble code that says "replace the MAF". When there is a code for no MAF output, it states what is going on. But is the failure the sensor or the circuit? This takes more troubleshooting.

But I approach things very methodically and specifically when it comes to MAF's, do everything to avoid telling someone to replace it. Real MAF's are expensive and I am only as good as the information that has been provided to me. Often there is a lot of back history I do not get informed of. I want to do the most thorough diagnosis before I suggest replacing a MAF. I also tell EVERYONE to keep what ever MAF is removed from the car as well.

While there are ways to "test" or "verify" the MAF flow measurement using a Volumetric Efficiency Test, this does not always work out like everyone thinks. Many of these MAF's degrade as they age by 5-15% and this is within the typical margin of error when performing a VE Test. I really do not suggest for people to attempt the VE test.

Think what you want, but there is a LOT more to all of this that most people realize!!
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temp, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose temp switch O-ring - BMW #13621743299
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Old 09-10-2016, 09:10 PM   #17
IcyMoustache
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jfoj.... the reason I have OBDfusion today is you. The forum should thank you in a big way and please dont take my comment as an accusation.

What I really mean is that the knowledge of this forum's members to be distilled into a good set of analyses that could be done on PIDs. The VE test is probably the simplest of tests and is a no regret move. While i understand that a VE that is within is margin of error is a grey zone. mine was at 40%!!! I could have done this long back. By the way I learnt the VE test from the forum itself. So turning back the knowledge is there in this forum. It just needs to be distilled into a single diagnostic guide. Maybe this Christmas I will sit down and put together such a one for the review of all you guys (And additions). We can then make it the definitive guide to using OBD to diagnose issues.

This way you (jfoj or other expert) need not spend individual time with all issues. People can read the guide and think for themselves.
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Old 09-10-2016, 10:51 PM   #18
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What is totally being missed here is there is not a specific PID that will give all the answers, they are only data points and clues.

From MANY years of dealing with these and many other makes and models of vehicles, there seems be be a few common denominators.

The majority of sensors degrade as they age, become worn or dirty depending on the sensor design and function. The problem is degradation in the 5-20% range is often hard to spot and quantify with many sensors.

However, a 40% problem should have been so very obvious it should knock someone out of their chair. The best case situation are hard failures, but with the exception of a few things like O2 sensor heater circuits and some other sensors, there are few "hard" these days. Most are degraded and on the edge that usually cause driveability problems and often codes that do not point to the specific problem sensor.

The other real problem that is happening is we are now dealing with cars that are 10-17 years old at this point. First, do you really expect a highly sensitive sensor to last more than 10 years/150k+ miles? Well some do, but many don't, they do however start to degrade over time.

Another really tough factor is many of these cars are on the 3rd+ owner with no real repair history. The MAF that happens to be under the hood may be the original, degraded MAF that is more likely to be under reporting. The MAF that is under the hood may actually be an Asian counterfeit that never worked properly but appears from all visual indications to be a OE/OEM sensor.

But the other side of this equation is the MANY garbage and counterfeit MAF's that are showing up in the market place, more and more each day. Many of the garbage and Asian counterfeit MAF's attempt to use cheap thermistors and home brew circuits in an attempt to make some cloned cast piece of plastic perform like an OE/OEM sensor for a small fraction of the cost. Many of these cloned plastic housing have fake Siemens/VDO part number stickers, so on the surface they may appear to be legitimate. These days almost anyone can mold plastic and print fancy labels from their home computer at their desk.

The problem is these garbage sensors may even have a fixed output at idle that closely mimic what a good sensor would measure, but under other conditions the same garbage sensor may over or under report the airflow and sometimes by a pretty wide margin. Then you have some of these sensors that may look good at idle and under WOT, but during the daily driving routine, they fall very short in proper measurement values.

These problems are not always easy to ferret out. The simple solution is to spend $200-$350 for a quality Siemens/VDO MAF from a reliable source and cross your fingers that the MAF needs to be replaced. To some extent, on a 10-17 year old car, a new MAF sensor and new O2 sensors is really the proper answer. None of these sensor will last forever. New camshaft position sensors are also advisable, as is a replacement fuel pump, filter and fuel pump relay. But all of this adds up and people are reluctant to do this level of maintenance on their vehicles. It really boils down to a cost/benefit that you feel comfortable with.

I am not one to promote MAF replacement, with most vehicles it is the absolute LAST sensors I ever recommend replacing. These cars are highly predictable and there are far more pressing problems that need to be addressed long before the MAF is blamed or replaced. But if you get an E46 these days, you really have no idea what sensors and parts are original, what sensors and parts have been replaced with non counterfeit parts and what parts are going to give you headaches first.

Given most people here are doing the work themselves on these cars, think about the hundreds and thousands of dollars in parts and labor you are saving doing your own diagnosis and repair. You also have control of what type of parts get installed on the car. You are likely adding to your tool collection and you are also learning as you go.

Wouldn't it be a crime if you took your E46 to a shop and they charged you $300-$500 to perform a diagnosis for Lean codes and they replace the MAF with a $50 part from the local parts store, throw away your original Siemens/VDO MAF that was working fine. Then you find out the car is not fixed and the problem is a torn CCV lower oil return line that is $15 from the dealer. Then you find out the $50 MAF that was installed is just compounding the problem, but you fall into the trap that the MAF can't be a problem because it was just replaced. This can really become a vicious cycle if you are not careful.

The above situation is a real world problem that goes on day in and day out in the automotive repair world. Maybe you can see from some of the above examples it is actually a bit harder to really figure out what is going on with any modern vehicle. The issue is DTC's or trouble codes and Live/Realtime data does not always point to a failed component, sensor or part. More often than not, you have to confirm what is working properly to then figure out what is wrong. Sometimes you get lucky with a guess or hunch, but this is rare it happens the first time.

Other components and parts may be easier to condemn than a soft/degraded MAF. A good shop/mechanic that works on specific makes and models would likely have "known good" test sensor that they can quickly swap in for a A/B comparison. But most of us do not have this luxury. Most electrical parts are NON RETURNABLE from parts suppliers and there are many reasons why.

I have been doing this a LONG time and some things are just not so easy and cut and dry. Especially when you are dealing with cars of this age with unclear/unknown service and repair history.

YMMV, but you might want to look before you leap and make sure you really understand the much larger picture.
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temp, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose temp switch O-ring - BMW #13621743299
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Old 09-11-2016, 08:12 AM   #19
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I can confirm what jfoj has written. I was chasing some weird codes, including the seemingly omnipresent P0171/0174 codes. The car was running so-so. Turned out the MAF was going bad. Spent $215 at FCPEuro for a new MAF. The engine now purrs.
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Old 09-11-2016, 09:23 AM   #20
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Open your app up and set up 2 numerical dials, one for long term fuel trim bank 1 sensor 1 and ltft bank 2 sensor 2. Come on its easy. What numbers come up? it also needs monitoring as it does move with highway/city driving.

This will tell you if your car really is running "perfect" whilst still code free. Also are all your monitors active as well?

Platinum is the same price as gold about 35 per gram. Not convinced your $18 new maf fixed it.

Sorry but you are the first I have come across online who is supporting an ebay maf.

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Just the moment I get a code or one pending, I'll let you know.
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