Aftermarket maf sensor

Hyundai MAF is only compatible with a limited number of these cars.

https://forum.e46fanatics.com/showthread.php?t=783659

https://forum.e46fanatics.com/showpost.php?p=11619983&postcount=17

You are not going to get good results with anything other than a genuine Siemens/VDO MAF sensor. History and others misery will pretty much confirm this. If the Hyundai MAF sensor is compatible with your car, you can try it, others seem to have been successful. I believe that item may be a Bosch unit, but I do not recall for sure, I have not re-read the posts.

The MAF is the absolute most sensitive and critical sensor on a modern engine. Attempting to measure airflow in grams per second over a wide range of variables is not easy. Every MAF that is manufactured needs to be tested and calibrated and the cheap off brand MAF do not always have the circuitry to actually allow calibration.

The other MAJOR problem these days is anyone can cast plastic, print labels and produce packaging. There are MANY, MANY counterfeit MAF's on the market, most come out of Asia, but there are also cheap "clones" that do not perform or measure accurate under all conditions. Another problem with many "after market" sensors even if they are simple sensors is the material thickness for something as simple as the male pins in the sensor can be too thin and cause intermittent and/or poor connection with the female terminals in the vehicle wiring harness connectors. So this is even an unforeseen issue to overcome or be aware of across the non OE/OEM sensor world.

The worst thing you can do to your wallet, your mental health and really frustrate yourself it to buy a cheap $50 MAF from your local auto parts store, ebay or Amazon and install is and then convince yourself the problem cannot be with the MAF because you replaced it with a new one. Well chances are you will finally circle back around weeks or months later after chasing your tail, spending more money and time on the car to then finally get a genuine Siemems/VDO MAF from a reliable source that then solves your problem.

You probably would have spent more than a genuine Siemens/VDO MAF would have cost in the end trying to go the cheaper route in the beginning. Think about it before you repeat history.

Good luck.

Have had a number of members that tried the Bremi with no so good results.

One thing everyone needs to understand is many of the cheaper MAF's use garbage sensors and circuits to measure airflow. They also do not have the ability to be "calibrated" or adjusted over a wide range of airflow conditions, this requires a lot more circuitry and will raise the cost of the device.

The cheap MAF vendors often just make sure the MAF reads reasonably accurate at idle, but they do not function well over the entire engine load. What happens is these cheap MAF's may solve idle related errors, but may be borderline or even trigger mixture related codes while driving.

Then everyone says to themselves, I just spent $140 or so on this NEW Bremi MAF, this cannot be the source of my problem. Then after spending a lot more time and money chasing their tails, they then spend more money on a genuine Siemens/VDO MAF and all their problems are resolved!

Be careful what you wish for, there is no free lunch when it comes to a quality Mass Airflow Sensor.

The MAF readings are "nominal" values. What everyone needs to understand is everything from the engine displacement, ambient temperature, altitude, base engine idle RPM, load on engine at time of checking the value such as AC or higher electrical load can and will cause the MAF value to be different.

We typically attempt to compare MAF readings at warm idle in Park/Neutral with no additional load. Nominal values we often see are in the range of around 3.4-4.2 g/s depending on engine size. BUT also remember, even a 5% change is close to 0.2 g/s. A 5% reduction in the MAF reading could be a soft failing/under reporting MAF, but before the MAF is condemned vacuum leaks need to be ruled out.

We are seeing a lot of these MAF's soft fail and typically under report between 5% and 15% and usually once the value is close to 10% then Lean codes can start to appear. Most of the under reporting is due to the MAF sensor being contaminated, however, the way the intake air path and CCV system are configured on a "stock" engine the contamination is RARELY hydrocarbon or oil vapor, it tends to be the silicon conformal coating on the MAF circuit board that starts to "flow" after years of high thermal cycles. This silicon conformal coating that flows CANNOT be cleaned off the MAF, it just need to be replaced.

Unfortunately there is no magic bullet test to determine if the MAF is a Pass or Fail part, you need some experience and you need to look at many different clues. While there are people that want to use the VE/MAF airflow test/calculator, I have found that these rarely will accurately flag an MAF that is under reporting by under 15%. The problem is there are a lot of variables with the VE/MAF testing and often people pick the wrong data to calculate with and end up with bad data. And if the test yields that the MAF is over 100%, then often this is clearly a calculation and/or problem with other data constants that are chosen/used.

As these cars age, past 10+ years, it is probably not a bad idea to just replace the MAF if there is anything suspicious about its performance and/or you are having Lean codes while cruising. The MAF and Pre-cat O2 sensors are not really Lifetime sensors, they degrade and need to be refreshed from time to time. O2 sensors are "consumables" and typically they should be replaced every 100-125k miles depending on the technology of the sensor. Narrow band/standard O2 sensors should be replaced at 100k miles, wideband 5/6 wire O2 sensors should be replaced every 125k miles. MAF replacement, well this is a wild card, but if you suspect if is giving you false results and under reporting, probably just best to replace it.

That's all great stuff. I can understand there's no hard and fast answer. Nominal is the key. So if Bosch say regular pre cat sensors need changing every 100,00 miles as PM why don't Siemens offer a similar recommendation for replacing MAF's. Is it because Bosch have a better marketing machine than Siemens ?? My local garage say they never change pre-cat sensors, ever.

I think there are a lot of differences in the way our cars run based partly on the differences in the fuel we get at the pumps here in Europe and the US and ambient operating temperatures. Another problem is the majority of E46's sold in Europe are NOT inline sixes. They are mostly 4 pot diesels so there's no strong knowledgebase

We don't get anything like the number of vacuum leaks you get and we tend to have negative fuel trims. I'm not sure how much the DME tune or fuel quality affects this. If we have these negative fuel trims, why do we have them and how much of an effect can a vacuum leak have on these negative trims and more importantly how easy would it be to find them by smoke testing.

I don't know but I think that European IL6 owners have a tougher time solving driveability problems even with OBD Fusion. Reading between the lines I think there are so many differences between US and European DME tunes. Maybe I should move to the US and buy one of your E46's or just go buy another diesel. Grrr

I think part of the problem is Europe (I have lived there for a few years, so I think?? I understand that part of the world to some extent) is in the cities people do not drive as much due to the cost of fuel, the distances they need to travel and the cheaper, readily available and more reliable public transportation. Due to this I think there are fewer shops and the shops do not have the volume of cars to service as we do here in the US. I think there are like 2.5 cars per household in the US or some crazy figure like that.

Even when European travel, trains are so much easier and cheaper than driving, I expect a lot of people take the train rather than drive. I hopped in the car a few weeks ago and did a 2500 mile road trip in a week, we do not think about doing this here in the US, in Europe, this would not be a common occurrence. Additionally owning a car and having a place to park it is not only expensive, but a pain in the butt at times.

So the problem with O2 sensors is not that there is much difference in the fuel or the operating temperature, it is more a full understanding on how the operate and how they degrade. O2 sensors RARELY trigger failure codes and when they do it is typically for a failed heater circuit. Rarely are there codes for degraded O2 sensors. See the graph below of a case of a member here who has some Pre-cat O2 sensors that were degraded and no codes. I think the car maybe had around 125-150k miles on the clock. I think in this case a picture is worth a 1000 words!!!

I do agree that a number of the European cars I have tried to sort out often had Negative Fuel Trim values, unclear if this is partially due to the EU DME tunes or a lack of Ethanol in the fuels?? But I think if the EU tunes are biased a bit more on the "Rich" side of fuel delivery, they are probably more forgiving of Lean codes by a few percent?

As for a standard MAF replacement interval, overall they are pretty robust, I think the specific problem with the Siemens/VDO MAF's on these cars is where they are located, how they are oriented with the circuit board on top and the higher under hood temperatures. The silicon conformal coating tends to "creep" or "flow" over time as the units age and the silicon coating can work its way onto the hot wire and insulate it causing the MAF to under report and under react. Might be interesting to attempt to mount the MAF upside down and see if the MAF will last longer before the conformal coating starts to creep/flow.

Lazy vs Fresh O2 Sensor Graph Below.

Yes we have a lot of cities with slow traffic. I'm not your typical European and I'm lucky to live in the suburbs where we have an abundance of parking and little traffic. ! I get through a tank of gas every week (and a litre of oil every 3 -4 weeks). I've put 50,000 miles on my car in 3 years. We don't do 2500 mile trips though I'll be doing an 800 mile trip in a few weeks and I'll have no worry about it. Most of my mileage is at 100 km/h on the freeway on cruise control driving between clients. I rarely do town driving only to drive my daughter to school.

The local garages here work mainly on old cars that are out of the standard warranty. The older the car one would expect the more knowledge they would have of that variant i.e 320d vs 320i. Fact is 11 out of every 10 E46's is diesel. You just don't see six cylinder E46's here. They exist only in small numbers. Funny thing is that the petrol variants are more forgiving, less prone to failure, and easier to fix that the diesels. IMHO.

I don't know if degrading MAF's trigger codes, i suspect not. Unfortunately you can't graph MAF's in a way you can graph O2 sensors or at least I've never seen it done. BTW I like your graphing methods, what are you using ? So MAF's are not the only victim of under-hood temps.

I'm gonna change my MAF.

A degrading MAF will not typically trigger a MAF related code, if there is a MAF code there are more obvious issues of failures. Soft failing MAF's that more often than no UNDER report the airflow tend to UNDER report in the range of 5-15% which is not so obvious to knock you out of your chair. You have to trace Fuel Trim values and have a "feel" for what may be going on. Clearly not an exact science.

Unfortunately there are SO many variables, it is almost impossible to positively identify a slightly degraded MAF directly and consistently.

As for the O2 sensor graphing, I use the OBDFusion App, configure it to Log before starting the engine after sitting overnight and then capture, export and graph the data. Often I need to manipulate some things to clean up the graphing and sometimes I have to narrow my view as well. The issue is this graphing works fine for older 4 wire non Wideband O2 sensors. Wideband 5/6 wire O2/Lambda/Air-Fuel sensors are not so easy to graph and condemn.

Has taken a lot of time, effort and practice to get the proper setup and manipulate the data in order to get the graphs, but I am comfortable with my current process.

As I tell people the MAF and O2 sensors are the far end sensors (first and last) that monitor and control the Air/Fuel mixture, emission output, performance and fuel economy of the vehicle. The MAF is in fact an "Input Sensor", the O2 sensor are more of an "Output Detector". While there are other "Input Sensors" on the car, there is really only one set of "Output Detectors", the O2 sensor(s). These are critical to the feedback and loop performance of the fuel management system and they are considered "consumables".