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Brooksthepro
10-20-2006, 02:56 PM
So my car has been getting the P0171 - Bank 1 system too lean CEL

I took it too the dealer and they said it was a faulty n75 valve. So they replaced that but the CEL came back up again right after i got it back. So i assumed it was probably the MAF, so i cleaned it by putting the whole sensor and housing into a ziplock bag with alcohol and let dry for 3hrs. Then went to autozone to clear my CEL.....it ran a little bit better, but the car seemed a bit sluggish still, especially in first gear. Basically the car seems a TINY bit faster then when its in limp mode, and then the next day the CEL came back on?

Any thoughts? Broken MAF? Boost leak? O2 sensor? even when the CEL is off the car still runs like theres bearly any boost.


TIA

marcini
10-20-2006, 04:03 PM
bad maf, primary O2 sensor, vacuum leak, all could contribute to lean conditons

SFexBOY
10-20-2006, 04:15 PM
had that error once....it was my MAF

IKE20VA4
10-21-2006, 08:52 AM
have that now...it IS my MAF. try unplugging it to see if that changes your outcomes at all. i went from 5psi with maf plugged in to about 15psi with it unplugged.

Brooksthepro
10-21-2006, 07:05 PM
Originally posted by 20VTURBOA4
have that now...it IS my MAF. try unplugging it to see if that changes your outcomes at all. i went from 5psi with maf plugged in to about 15psi with it unplugged.

!!!! thanks man! i did that tonight and reset the CEL and BINGO it ran like a champ!

how long would you guys say it is safe to run the car without a MAF....long enough for me to get another one? or should i plug it back in untill i get another one?

bitterchild
10-21-2006, 08:33 PM
BABAupdownBAleftrightBA St!!!!!!

Brooksthepro
10-22-2006, 01:20 PM
wtf?????? lol^^

BoostFrenzy
10-22-2006, 01:38 PM
uhh unplugging the maf altogether is the stupidest thing you can do, the MAF reports to the ecu how much air is flowing through the engine, that code can mean there's a pre-turbo leak between the maf and the inlet of the turbo, check your connections and if it's still an issue, swap the maf but NEVER run with it unplugged!

SFexBOY
10-22-2006, 01:39 PM
Originally posted by bitterchild
BABAupdownBAleftrightBA St!!!!!!

for a sec there I thought that was the code to "Contra" for Nintendo:

upupdowndownleftrightleftrightBABA selectstart!!!!

bitterchild
10-22-2006, 01:46 PM
I think it's tmnt. Contra would have been a better choice you're right.

BoostFrenzy- drive by wire a4's have both a maf and a map so they can drive w/o a maf signal and work of existing tables based on map input. It's a backup system in case the maf signal is implausible since they do fail regularly.

BoostFrenzy
10-22-2006, 01:55 PM
Originally posted by bitterchild
I think it's tmnt. Contra would have been a better choice you're right.

BoostFrenzy- drive by wire a4's have both a maf and a map so they can drive w/o a maf signal and work of existing tables based on map input. It's a backup system in case the maf signal is implausible since they do fail regularly.

I understand that, as most cars turbo cars have both (i was surprised to learn my 99 only has maf), however the maf is there to help with atmospheric changes... you can't rely on speed density alone

bitterchild
10-22-2006, 02:20 PM
the car also has a barometric sensor as does pretty much every efi car since the early 90's. Plenty of oem manufacturer's run speed density alone. Honda for example.

BoostFrenzy
10-22-2006, 02:36 PM
Originally posted by bitterchild
the car also has a barometric sensor as does pretty much every efi car since the early 90's. Plenty of oem manufacturer's run speed density alone. Honda for example.

barometric pressure / speed density + boost != actual airflow through engine, you're flowing MORE air at theSAME barometric pressure level with colder temps... WHY ELSE do you think they use both ?

come on man quit arguing with me unless you're informed :/

Brooksthepro
10-23-2006, 09:21 AM
ok so since my car IS dbw. it is safe to drive without the maf sensor? for a few days?

since i know its the maf sensor cuz since its been unplugged the car runs beautifully

bitterchild
10-23-2006, 10:29 AM
atmospheric changes are generally relative pressure and humidity. The a4's also have an intake air temp sensor as well as an outside thermometer.

I already told you they have both because the map circuit is a backup for the maf system. It also functions to add onboard diagnostic function to the turbine and it's boost control system.

I'm not argueing with you, I'm telling you how these cars work since you don't know. You can tune reliably off of speed density alone (as honda has since efi) but Bosch ME7 is based off the MAF w/ a MAP piggybacked on.

Brooksthepro
10-23-2006, 05:00 PM
so...u guys havent answered my question lol?

BoostFrenzy
10-23-2006, 05:10 PM
Originally posted by bitterchild
atmospheric changes are generally relative pressure and humidity. The a4's also have an intake air temp sensor as well as an outside thermometer.

I already told you they have both because the map circuit is a backup for the maf system. It also functions to add onboard diagnostic function to the turbine and it's boost control system.

I'm not argueing with you, I'm telling you how these cars work since you don't know. You can tune reliably off of speed density alone (as honda has since efi) but Bosch ME7 is based off the MAF w/ a MAP piggybacked on.

honda isn't boosted and dealing with considerably more airflow given optimal atmospheric conditions, but whatever yeah run your car with the maf malfunctioning, they just put both on there so it had a "backup" [rolleyes]

bitterchild
10-23-2006, 05:49 PM
I'm not telling anybody to tune their dbw audi w/o the maf I'm just commenting in regards to your original post telling everybody to "NEVER run with it unplugged".

Most tuners would agree that speed density is their preferred method of air metering for performance tuning and that mass air is best suited for cases where driveability, fuel economy, emissions and adaptation to conditions are the priorities.


Brooks- you can drive the car w/ the maf unplugged fine, I would recommend just not driving the piss out of it or anything. The fact that the car idles and runs well w/ the maf unplugged does make a convincing case towards the maf element being faulty. Go ahead and replace that at your earliest convenience but don't lose sleep over driving the var to work mafless while you wait for the new maf to come in.

Brooksthepro
10-23-2006, 05:56 PM
thanks for your input [up] [:D] MAF will be on its way ASAP