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Old 10-20-2008, 10:23 AM   #1
jbeurotech
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Testing Maf sensor How to do it

It's called Volumetric Efficiency and is a measurement in percentage of the actual ability of the engine to move air versus what it could move in a perfect world. To use this test, you need a scan tool capable of recording data and a VE Calculator like this one. The calculator requires the engine size in cubic inch displacement, airflow in grams/second, engine rpm and intake air temperaure when tested. Set your scan tool to record these PIDs (Parameter Identifications) and take the car out for a test drive. If you want to test the accuracy of the MAF sensor, record the fuel trim PIDs (STFT and LTFT) as well.

From a rolling start in first or second gear, perform a wide open throttle run while recording the data. Make 3 or 4 passes in order to compare results. Back at the shop, find the point in your recording where airflow reported by the MAF and engine rpm are at their highest. Enter these values into the calculator. The result is a percentage to "ideal". Ideal would be 100% of the engine's displacement. However, "ideal" is not real world and normal efficiency is generally 80% or more. Turbocharged and supercharged engines will run higher than 100%, naturally, so bear that in mind if testing an engine so equipped.

If VE is low, and fuel trims are correcting positive (for a lean condition), then suspect an inaccurate reading from the MAF sensor. If VE is low, and fuel trims are normal, then look for restrictions to air flow. A "running" compression test can help isolate whether the restriction is on the intake side of the combustion chamber or the exhaust side.

The VE calculator is another diagnostic tool that can provide quick direction in diagnosing various driveability complaints. But just is as the case with other diagnositic tools, it should be followed by more pinpoint tests to verify the results...and the failure.


Now if someone would be kind enough to give me a place to host the file I will make the VE calc available for download
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Old 10-20-2008, 11:53 AM   #2
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Wow six view guess no one needs this info they would rather just replace expensive parts.
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Old 10-20-2008, 11:59 AM   #3
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good info but i dont think to many people have the tool required for this job laying around in their tool box....that might explain the lack of replies...but its really good info...thanks for sharing
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Old 10-20-2008, 12:00 PM   #4
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lol good post..this will come in handy next time. I'm sure videos would help many in here in additon to your write ups.
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Old 10-20-2008, 12:02 PM   #5
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Should probably be on the DYI forum, right? What is the scan tool? The peake tool or something else?

Awesome write up jbeurotech..
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Old 10-20-2008, 12:06 PM   #6
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Should probably be on the DYI forum, right? What is the scan tool? The peake tool or something else?

Awesome write up jbeurotech..

http://forum.e46fanatics.com/showthread.php?t=596502
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Old 10-20-2008, 12:11 PM   #7
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yeah, I love your threads trying to help us out, but Most of the things in your posts are way over my head. The cost of buying these tools or doing this or that is just not worth it compared to an Indy diagnostic fee. Don't get me wrong, I know I really appreciate your efforts but sometimes us fanatics don't have access to the things needed to perform these tests. But thanks for teaching us.
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Old 10-20-2008, 12:17 PM   #8
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Any cheap scan tool that can read data will work fine. As far as the VE calculator it is very easy to use if someone can host the file I will upload it for everyone to have.

This tool looks like it would even work for this basic test
http://www.dealextreme.com/details.dx/sku.16546

I think some of the Autozone ones that you rent even do live data.

HERE IS A SCREEN SHOT OF A GOOD MAF
Attached Files
File Type: pdf ve CALC GOOD.pdf (6.1 KB, 934 views)
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Last edited by jbeurotech; 10-20-2008 at 12:26 PM.
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Old 10-20-2008, 12:28 PM   #9
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Here is a bad maf on a Toyota(I know why was i working on one of those..... Long story!!)
Attached Files
File Type: pdf VE Toyota.pdf (10.4 KB, 586 views)
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Old 10-20-2008, 12:41 PM   #10
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Is that better I am still learning what you know and don't and how best to help you. Trust me I am not trying to talk over you guys. I thought this was a simple straight forward test. let me know what gives you troubles about it and we can have a discussion and see if people can get through it
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Old 10-20-2008, 02:58 PM   #11
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Seth, I will gladly host the file for you (if it's not HUGE). Email me - ken@bimmertools.com.

Regarding the Peake tool's capability of recording the required data, they do not offer that feature. This is why the customers that demand live data tend to opt for a generic tool with that capability. Keep in mind that the generic tools differ from the Peake tools in that they don't read the BMW specific diagnostic codes. The Peake tools are a single-purpose, BMW-specific code reader/reset tool - not a data logger. Two distinct types of products, both have benefits. Most of my customers prefer the functionality and accuracy of the Peake tools (as described in the article linked above and in my sig).

Ken
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Old 10-20-2008, 03:09 PM   #12
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Ok sent it to Ken who should have a link for you guys soon have fun!
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Old 10-20-2008, 03:23 PM   #13
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Autozone code readers do have this thing to record live, just plug it up and scroll through the menu instead of choosing enter to read codes.
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Old 10-20-2008, 03:25 PM   #14
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Autozone code readers do have this thing to record live, just plug it up and scroll through the menu instead of choosing enter to read codes.
Perfect there you go you can do all of this for free!!! Now someone should do this before and after cleaning there maf and record the results to test the effectiveness of this cleaner.
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Old 10-20-2008, 08:46 PM   #15
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What a clever little calculator!

You can find the link at the top of our diagnostic tools page - www.bmwscantools.com. It is a very small .exe file - click the link and save the file.

Thanks, Seth!

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Old 10-20-2008, 08:53 PM   #16
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Works good to thanks for getting the file up
direct link http://www.alkendesign.com/ve.exe
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Old 10-20-2008, 10:35 PM   #17
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Thanks to both you guys. Ill be downloading this over the weekend when Im cleaning my MAF and changing plugs, etc.

You guys rock
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Old 10-22-2008, 12:03 PM   #18
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Top for guy with Maf issue
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Old 12-04-2008, 12:03 AM   #19
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Question. MS43 3.0 - running poorly, misfiring, and accrid white smoke....unplug new MAF since I was no longer using the MS45 DME and wiring harness (swapping the 3.0 / 6spd into a 325 auto wagon)....

anyway - unplug the new MAF and the car runs fine, idles great, no surging of rpm's, no misfires, can rev the engine without it dying...plug the maf back in...all goes to sh1t

I am turning the car off each time before plugging and unplugging. I had thought it was a fuel, spark or vacuum problem(s) up until I figured out the problem with the wagon by accident - I unplugged the MAF and then prepared to tear other things apart...then remembered I wanted to spray starter fluid to check for vacuum leaks and started the car (with the MAF still unplugged) and it ran perfect...no missing, no surging and no rich fuel smoke out the exhaust....turned it off - plugged in the MAF and it ran like crap again...missing, surging, etc....

Unplugged the MAF - ran fine. So tomorrow I am going to test the MAF wiring and the MAF and try to get a replacement or test MAF
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Old 12-04-2008, 02:25 AM   #20
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Perfect there you go you can do all of this for free!!! Now someone should do this before and after cleaning there maf and record the results to test the effectiveness of this cleaner.
Why do I get the feeling you already know the answer to this? Is it modern day snakeoil? I'de do the test but I don't have a dirty MAF to test. Mine was replaced recently.
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