MAF and other related questions
#1
04-02-2007, 05:29 PM
MAF and other related questions
Just looking for some info. on MAFs, what they do, etc.
As I understand it, they basically tell the ecu how much air is flowing, and then the ecu determines the amount of fuel to send. Is that right? Also, as the car is modded (chip, turbo, etc.) does the engine draw in more air, thereby increasing the air flowing past the MAF, thereby telling the engine to send more fuel?
Another question, when you disconnect the MAF, how does the engine accomplish all this? Is there some type of 'base' setting that the ecu uses? and is this base setting optimal? i hear that if your MAF is bad, that if you disconnect it, it should run better - but will it run optimally? If your MAF is working perfectly and you disconnect it, will you see a decrease in performance?
Just wondering, since the shop suggested my MAF might be going bad - which could be causing the pinging and the lackluster performance i've been having. But when i disconnect the MAF, the car still runs exactly the same. I'm taking it in later today, but it just got me thinking, and I'd like to understand a little bit better how it all ties in together.
Thanks.
As I understand it, they basically tell the ecu how much air is flowing, and then the ecu determines the amount of fuel to send. Is that right? Also, as the car is modded (chip, turbo, etc.) does the engine draw in more air, thereby increasing the air flowing past the MAF, thereby telling the engine to send more fuel?
Another question, when you disconnect the MAF, how does the engine accomplish all this? Is there some type of 'base' setting that the ecu uses? and is this base setting optimal? i hear that if your MAF is bad, that if you disconnect it, it should run better - but will it run optimally? If your MAF is working perfectly and you disconnect it, will you see a decrease in performance?
Just wondering, since the shop suggested my MAF might be going bad - which could be causing the pinging and the lackluster performance i've been having. But when i disconnect the MAF, the car still runs exactly the same. I'm taking it in later today, but it just got me thinking, and I'd like to understand a little bit better how it all ties in together.
Thanks.
#2
04-02-2007, 05:34 PM
RE: MAF and other related questions
it's been covered so many times... use search...
bt here's a good link http://www.europeancarweb.com/tech/0...s_replacement/
bt here's a good link http://www.europeancarweb.com/tech/0...s_replacement/
#3
04-02-2007, 05:47 PM
RE: MAF and other related questions
I did use search. I spent the last hour reading about them.
I couldn't find anything about the defaults used when the MAF is disconnected, or how that process works. Are there certain air flow rates that are measured, and depending on that, fuel is sent to the engine accordingly?
I couldn't find anything about the defaults used when the MAF is disconnected, or how that process works. Are there certain air flow rates that are measured, and depending on that, fuel is sent to the engine accordingly?
#4
04-02-2007, 05:57 PM
RE: MAF and other related questions
Yeah I've been searching for the past few hour too. its not as easy as you think - you search "disconnect maf" you get every thread where someone said to try that out. here is a write-up on how to remove the MAF http://forums.audiworld.com/a4/msgs/2644088.phtml . also this is from the 1.8t common trouble shooting guide in the stickies
MAF – Mass air flow meter is used to measure the air going into the engine. It is located on the outlet of the airbox, and housed in a cylindrical tube. The ECU reads the MAF signal, and injects fuel in proportion to the airflow. There are a few different ways the MAF can fail. The MAF can get coated with oil, and will not read properly. This is common if it happens right after installing a CAI, or a K&N filter. It can be cleaned out with 99% isopropyl alcohol, or a quality electronics cleaner. Remove the sensor from the housing and clean the sensor element.
MAF sensors also go bad due to too much airflow. On a car with a larger turbo the airflow is so high that the MAF element will get burned out from the excess air flow. It is common to increase the size of the housing to prevent this (other modifications required).
To check for a BAD MAF the best way is with a VAG com. Block 002 show air mass from the sensor. At idle the air flow should be 2-4 grams/second. With a wide open throttle run to redline the reading should show up to 170 g/s on a chipped car. Look for jumpy readings in the MAF, which can indicate a problem. More details here http://www.ross-tech.com/vag-com/cars/fuel-trim.html if you suspect your MAF is bad, one way to test it is to unplug the MAF, often if the MAF is giving false readings and upsets the fueling. If you unplug it, the ECU will ignore the MAF and run off of baseline tables. Be careful, as a boost leak or a vacuum leak can be miss-diagnosed as a bad MAF, because they will throw off the readings on the MAF. (Air sneaks around the MAF).
MAF sensors also go bad due to too much airflow. On a car with a larger turbo the airflow is so high that the MAF element will get burned out from the excess air flow. It is common to increase the size of the housing to prevent this (other modifications required).
To check for a BAD MAF the best way is with a VAG com. Block 002 show air mass from the sensor. At idle the air flow should be 2-4 grams/second. With a wide open throttle run to redline the reading should show up to 170 g/s on a chipped car. Look for jumpy readings in the MAF, which can indicate a problem. More details here http://www.ross-tech.com/vag-com/cars/fuel-trim.html if you suspect your MAF is bad, one way to test it is to unplug the MAF, often if the MAF is giving false readings and upsets the fueling. If you unplug it, the ECU will ignore the MAF and run off of baseline tables. Be careful, as a boost leak or a vacuum leak can be miss-diagnosed as a bad MAF, because they will throw off the readings on the MAF. (Air sneaks around the MAF).
#5
04-02-2007, 06:07 PM
RE: MAF and other related questions
Thanks for the info.
I noticed that it said "With a wide open throttle run to redline the reading should show up to 170 g/s on a chipped car."
So what is the 'stock' setting? In other words, when the MAF is disconnected, what would the ecu 'guesstimate'?
Can I also assume that as mods are added (HP is added) the '170 g/s' number will go up?
I noticed that it said "With a wide open throttle run to redline the reading should show up to 170 g/s on a chipped car."
So what is the 'stock' setting? In other words, when the MAF is disconnected, what would the ecu 'guesstimate'?
Can I also assume that as mods are added (HP is added) the '170 g/s' number will go up?
#6
04-02-2007, 06:20 PM
RE: MAF and other related questions
If you unplug it, the ECU will ignore the MAF and run off of baseline tables
#7
04-02-2007, 06:59 PM
RE: MAF and other related questions
unplugging the MAF should only be used as a test and you should try not to actually drive your car around too much with it unplugged - the reason for this is even though your car seems to be running better it will be running in a rich condtion and will throw a CEL and that is not good. so as for what the ECU would see during WOT when the MAF is unplugged - shouldn't be a question.
#8
04-03-2007, 02:35 PM
RE: MAF and other related questions
Can anyone give me their MAF g/s readings?
I got mine tested yesterday, and after installing a new MAF, I'm at about 140 g/s. This seems pretty low to me, given that i'm chipped with FX and injectors. Someone above posted that it should be about 170 g/s chipped.
I got mine tested yesterday, and after installing a new MAF, I'm at about 140 g/s. This seems pretty low to me, given that i'm chipped with FX and injectors. Someone above posted that it should be about 170 g/s chipped.
#9
10-02-2009, 12:56 AM
Just referring to how the car is supposed to run when the MAf is disconnected, I tried this today because i have been experiencing idle issues and when i started the car up with MAF unplugged it started then died. The engine seemed to start up higher than usual then try and idle at 400-500rpms so it died. Any ideas what would cause this?
i have a 2000 a4 2.8 Q auto
i have a 2000 a4 2.8 Q auto
#10
02-11-2010, 10:15 PM
with mine, with the MAF disconnected, there was a minor hesitation at throttle tip-in. i just dont understand how a motor run with the air flow meter disconnected.
Last edited by archebald23; 02-15-2010 at 09:55 PM.
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