Switched back from custom tune to stock to pass smog out here in Cali. That seemed to open the can of worms because it subsequently caused the p0171 code. Broke down and took to mechanic and they replaced air intake and and o2 sensor. That still didn't do the trick so they wanted to charge me another $300 to replace MAF sensor. I told them no and ordered one myself since they are easy to install. Also, need to change CAI filter as it's getting pretty old. I cleaned it off well, but still needs to be replaced.


The car runs great, no power loss or rough idle other than that dumb CEL.

After I install that, if I am still throwing the system too lean code, what else could it be?


Thx for help!

Specs- 2007 Mustang GT, 77K miles- no mods other than shorty headers and CAI.

 

it may be time to change your fuel filter if you haven't already done it. it could be plugged up and not flowing enough fuel to the injectors to keep it rich enough.

 

http://www.obd-codes.com/p0171

Most likely its a vacuum leak between the MAF and the cylinders, or an exhaust leak between the block & upstream O2 sensor on the passenger side.

A plugged fuel filter would cause a lean condition on both sides of the motor, but its not a bad idea to change it if you haven’t in a while.

Good luck...

 

Thanks for the suggestions! Actually, its already been checked for vacuum leaks twice and they replaced the intake. Fuel filter was changed, as well. I still have the one code, P0174 (not p0171, mistaken) on bank 2. I'm getting the MAF sensor in the mail tomorrow and so I'm keeping my fingers crossed. Any more suggestion? Thanks again!

 

http://www.obd-codes.com/p0174

I doubt changing the MAF is going to fix your problem since the code is specific to one side of the motor (the drivers side with the p0174 code). If your confident that there are no vacuum leaks, then check for exhaust leaks between the block & first o2 sensor on the drivers side. Its simple to do. Get a squirt bottle of soapy water and hose down the exhaust manifold and where it mounts to the block, the exhaust manifold to exhaust pipe connection, and all the pipes in-between. While its still wet, start the car. If there is an exhaust leak you’ll see bubbles. Good luck...

 

i recently had that code come up on my mazda, which measures the differential pressure in the filter housing. when i replaced the filter i didn't put the housing back on properly causing a slight diversion around the filter. code came up within 10 miles of driving and made me scratch my head for a bit until i noticed one side of the filter housing was not seated well... hopefully your issue is a simple one like that.