maf sensor test? car still runs the same with it unplugged

[euronyc]

started my car and unplugged the maf and the car still runs the same. does this mean the maf sensor is dirty/bad?

im trying to fix some issues on my 2005 audi 1.8turbo cabriolet

http://www.audizine.com/forum/showth...83-16684-16686

[euronyc]

??

[rocket1420]

no

[ADCS]

Yes.

[K04-B6]

You need to take a look at your readings with either a scanner that can read live data or Vag-com. You won't get anywhere without numbers and data.
Mine does the same but my MAF readings are good when it's plugged in. When it's plugged in I run lean in-between +18 to +22. When I run it unplugged my numbers start to drop to the normal operating numbers... So I'm at a lost too.

Good luck

[euronyc]

this is what ive read up on so far


with the car running if you unplug the maf the car is suppose to shut off that means the maf is good and its working.

with the car running if you unplug the maf and it stays running then its not working.

[K04-B6]

this is what ive read up on so far


with the car running if you unplug the maf the car is suppose to shut off that means the maf is good and its working.

with the car running if you unplug the maf and it stays running then its not working.

I've read that as well. To me, information about the MAF is very confusing, My car runs well with the MAF plugged and unplugged, when the MAF is plugged my idle and redline readings are within spec but I run lean. If I unplug it, the car runs well and my readings for long term fuel trims go back down.

This is what I find confusing, lets say my MAF is bad, If I unplug it the car should technically run like crap anyways since there's no more MAF readings? I don't understand that if I have a good MAF on and unplug it the car should run like crap.. How does it know I have a good MAF on if it's unplugged???

Please pardon my dumb questions but I really hope someone can shed light on this subject. And I apologize if this is viewed as thread jacking. I'm just trying to clarify general information on the topic and hopefully it can help both of us.

[euronyc]

I've read that as well. To me, information about the MAF is very confusing, My car runs well with the MAF plugged and unplugged, when the MAF is plugged my idle and redline readings are within spec but I run lean. If I unplug it, the car runs well and my readings for long term fuel trims go back down.

This is what I find confusing, lets say my MAF is bad, If I unplug it the car should technically run like crap anyways since there's no more MAF readings? I don't understand that if I have a good MAF on and unplug it the car should run like crap.. How does it know I have a good MAF on if it's unplugged???

Please pardon my dumb questions but I really hope someone can shed light on this subject. And I apologize if this is viewed as thread jacking. I'm just trying to clarify general information on the topic and hopefully it can help both of us.

lol no not a dumb question at all lol pretty much in the same boat. just cant seem to find a rock solid answer

[K04-B6]

What kind of issues are you having?

[euronyc]

http://www.audizine.com/forum/showth...83-16684-16686

[K04-B6]

http://www.audizine.com/forum/showth...83-16684-16686

Are you still getting all three codes?

P16683 seems to be related to your N75 valve from a quick search. Either it's that sensor or you have a leak somewhere. I've had a problem with that valve before but it never threw a code for me. The way I tested it is I bought a used one from the scrap yard and brought it home, blew through both holes and the flow was equal for both. When I took the one off my car I could only blow well through one side of the openings. There's three openings on the valve but I think I blew from the point where it enters the tip and covered one of the extra holes with my finger and vice versa. After I installed the N75 I got from the junk yard my problems went away. Since you're getting a code yours might actually be faulty as in you need to replace it.

P16684 and 16686 are pointing towards misfires on cylinders 2 & 3, What I would do is swap your coil packs around, swap coil pack 1 with 2 and swap coil pack 3 with 4, run the car and see if you get codes for misfires on cylinder 1 & 4 , if so that means you need two new coil packs, if it still gives you a misfire on 2&3 then it's most likely your connectors or your harness.

The best thing to do would be to run a smoke test to see if you have any leaks in your system.

Hope this helps a little.

[old guy]

this is what ive read up on so far


with the car running if you unplug the maf the car is suppose to shut off that means the maf is good and its working.

with the car running if you unplug the maf and it stays running then its not working.

The ECU utilizes numerous different inputs to control the fueling. Obviously the MAF sensor is a major component. Also utilized is the front wideband oxygen sensor, the MAP sensor, the rear CTS, the IAT sensor as well as the throttle position sensor.

When you unplug the MAF sensor the ECU utilizes predetermined maps that incorporate all the other inputs to determine the fueling requirements. So typically if everything is in check and working properly unplugging the MAF sensor should not make much of a difference. If anything the ECU will move slightly to the rich side to protect the engine.

If you have a problem somewhere such as a small air leak or dirty MAF sensor the MAF sensor will not meter all of the intake air. The ECU will “see” this through the front wideband oxygen sensor and adjust accordingly. Then when you unplug the MAF sensor you will notice a change in the performance. It can be from something small to something major, depending upon the conditions that the ECU is adjusting for.

[K04-B6]

The ECU utilizes numerous different inputs to control the fueling. Obviously the MAF sensor is a major component. Also utilized is the front wideband oxygen sensor, the MAP sensor, the rear CTS, the IAT sensor as well as the throttle position sensor.

When you unplug the MAF sensor the ECU utilizes predetermined maps that incorporate all the other inputs to determine the fueling requirements. So typically if everything is in check and working properly unplugging the MAF sensor should not make much of a difference. If anything the ECU will move slightly to the rich side to protect the engine.

If you have a problem somewhere such as a small air leak or dirty MAF sensor the MAF sensor will not meter all of the intake air. The ECU will “see” this through the front wideband oxygen sensor and adjust accordingly. Then when you unplug the MAF sensor you will notice a change in the performance. It can be from something small to something major, depending upon the conditions that the ECU is adjusting for.

Thank you for all the very insightful information Old Guy! From your information I gather that my MAF is probably still good, I'll have to clean it though to see if maybe there's a little bit of debris on it. Since the TPS plays a part in there I should probably do a TBA then? Or would this have nothing to do with how high my LTFT's are? I still need to smoke test my exhaust to verify for any leaks at my manifold and surrounding areas.

[coffeysm]

I wouldn't rely on just unplugging the MAF test when it comes to running rich or lean. Most cars will run in a preconfigured rich mode when the MAF is unplugged and also go off other sensors like old guy stated. I got burned real bad doing only this test on my Infiniti tracing down a huge vacuum leak. A Nissan master tech told me to do this same test and when I did it, I figured oh okay my MAF is bad. I ended up wasting 300 bucks on a perfectly good working part. The problem ended up being a 15 dollar o-ring behind my brake booster, I figured it out after building a home made smoke machine.

I have another issue with my A4 3.0 both banks are 0172/0175 running rich. I unplugged the MAF and nothing really changed and that's because my LTFT are maxed out with -25%, so there was not much of a performance change. I've read that you should get about 1g/s for each liter increasing by 500RPM at idle, so my 3.0 idles around 720RPM and my MAF was reading 4.5-5+ g/s at idle which I think is close. Ross-Tech also mentions at WOT you should get close to .8 * HP g/s. So, my B6 3.0 has 220 * .8 = 176 g/s...when I was doing this test my fuel pump decided to crap out on me, lol. I did get as high as 146 g/s before that happened though, I have a feeling it might be due to my engine timing. I did my timing belt a few months back, however, I'm not getting any timing codes, misfires, or anything like that. It wasn't until I looked at group 93 and saw my degrees were slightly off. I'm still going to verify my AFR, O2, MAF, and replace that fuel pump as well prior to messing with my timing belt though.

I'd look up realfixesrealfast or Schrodinger's Box they both have some real good YouTube videos discussing MAF, LTFT, STFT, etc...

[old guy]

Thank you for all the very insightful information Old Guy! From your information I gather that my MAF is probably still good, I'll have to clean it though to see if maybe there's a little bit of debris on it. Since the TPS plays a part in there I should probably do a TBA then? Or would this have nothing to do with how high my LTFT's are? I still need to smoke test my exhaust to verify for any leaks at my manifold and surrounding areas.

This thread might be worth reading. It contains a bunch of general info on troubleshooting a lean condition: Clicky click®

[K04-B6]

This thread might be worth reading. It contains a bunch of general info on troubleshooting a lean condition: Clicky click®

Definitely a good read! Thank you for that link. Hopefully I end up finding my issue and when I do I'll definitely post my success!

Sent from my SM-G930W8 using Audizine mobile app

[euronyc]

Are you still getting all three codes?

P16683 seems to be related to your N75 valve from a quick search. Either it's that sensor or you have a leak somewhere. I've had a problem with that valve before but it never threw a code for me. The way I tested it is I bought a used one from the scrap yard and brought it home, blew through both holes and the flow was equal for both. When I took the one off my car I could only blow well through one side of the openings. There's three openings on the valve but I think I blew from the point where it enters the tip and covered one of the extra holes with my finger and vice versa. After I installed the N75 I got from the junk yard my problems went away. Since you're getting a code yours might actually be faulty as in you need to replace it.

P16684 and 16686 are pointing towards misfires on cylinders 2 & 3, What I would do is swap your coil packs around, swap coil pack 1 with 2 and swap coil pack 3 with 4, run the car and see if you get codes for misfires on cylinder 1 & 4 , if so that means you need two new coil packs, if it still gives you a misfire on 2&3 then it's most likely your connectors or your harness.

The best thing to do would be to run a smoke test to see if you have any leaks in your system.

Hope this helps a little.

i did the soap water test and found no leaks the coils and spark plugs and intake tube are brandnew from the previous owner with receipts from the mechanic shop.

misfires only on start up then runs normal

will check the n75.

[K04-B6]

i did the soap water test and found no leaks the coils and spark plugs and intake tube are brandnew from the previous owner with receipts from the mechanic shop.

misfires only on start up then runs normal

will check the n75.

I would still suggest trying a smoke test or a boost leak test. You can build your own smoke machine for pretty cheap, there's a few DIY on youtube. I find the soap test doesn't always find the problem as you can miss some areas ect..

[rocket1420]

Yes.

No. If the car runs the same with the MAF unplugged, the problem is NOT the MAF.

If you unplug the MAF and things get better, the problem is with the MAF. This is because the ECU ignores the faulty MAF readings since it's unplugged. It uses a different fuel strategy without those readings.

So to the user above who unplugged his MAF and got better fuel trims, your MAF is bad. You should be able to verify this in VCDS.

[rocket1420]

i did the soap water test and found no leaks the coils and spark plugs and intake tube are brandnew from the previous owner with receipts from the mechanic shop.

misfires only on start up then runs normal

will check the n75.

Soap water test won't find a vac leak, at least not by showing bubbles. It's a vacuum leak, not a pressure leak. If you manage to spray water directly into the leak, the car should run worse. That would be your only clue without a smoke machine.

However, your problems are related to things that you don't want to fix in your other thread. Unless you did fix them. I haven't checked that thread yet.