Hi ,

I have a problem with a code P0171 . I changed a MAF sensor , Oxygen Sensor , cleaned Pcv Valve and everything is OK and no leaking , holes . But there is a lack of power and engine rev is low I think . I still have the code problem and does anyone can help me ? is it for exhaust ? Thanks

 

Welcome to the forums!! Can you please tell us what car you have (year, model, engine e.t.c.) this will help ALOT more than just searching for random DTC codes, you can add it to your signature (use mine for example) so you dont have to add it to every post

 

P0171 is a "lean" code. Primary cause is a vacuum leak. the Air intake hose tends to crack at the ribbed section. you may not see the cracks unless you bend the hose there. If there are cracks you may use duct tape over the ribbed section of the air intake hose.
What method did you use to check for vacuum leaks?

 

My car is Mazda Protege 1999 LX 1.6 ... my friend told me clean the manifold , any ideas ?

 

imaco: " lean" means there is more air going into the engine than the MAF sensor measures. Therefore the computer adds not enough fuel for proper combustion.

So, somewhere between the MAF sensor in the air filter housing and the cylinder head there is a hole where extra air gets sucked in.
Check the air intake hose as I described, please! Check also the hoses that connect to the air intake hose, throttle body and intake plenum. These are the PCV hose, brake booster hose, vacuum hose for the EGR boost sensor, vacuum hose for the fuel pressure regulator. Did I forget any?
In a bad situation the lower intake manifold gasket may be leaking.
Idle the engine and listen for hissing sounds. Or check some Youtubes on how to find a vacuum leak.


You can replace the small vacuum hoses right away, it's cheap. But find the leak first before you take things apart.

 

A quikie on maf sensors. These are pitot (heated) tubes that measure cfm across it. They also are sized to the air inlet. Heated is because in order to measure flow, temp has to be in the equation. If your air plenum has a hole, rip, whatever that unmetered air is entering it will have a major affect on air/fuel ratio. The maf is telling the pcm what is going across it in the form of not only a refernce signal i.e 0-5 volts, but measures what comes back, calculates cfm for fuel mixture. This is a mistake some people make when resizing or altering the inlet plenum as the pcm has to be reprogramed as the reference voltage will not be the same in reference to the air flow.

 

So could you tell me what exactly I should do ? After changing MAF and oxygen sensor the mechanic told me go to dealership and get another MAF sensor , I bought it from autoparts and he said your car is fine and no problem just get another MAF ?what do you think ? You mean I need to change Air Plenum or CFM or any other thing ? Pitot tubes ?

 

You need to investigate for air entering the system that isn't going through the maf i.e. plenum leaks, and or vacuum leaks.

 

Do you have an aftermarket intake, that is not stock. If tube is bigger than stock then you may need an air straightener: Silicone Hose, Silicone Hoses, Turbo Hose, Turbo Hoses, Intercooler Hose, Intercooler Hoses, Turbo Connectors,T-bolt Clamps,Race-Proven Quality by HPS Performance Racing Products Scroll down a bit on page

 

Thanks guys ... Be honest guys I am not a mechanic but my mechanic investigated for vacum leak and smoke and he saw nothing ... he said can be for O2 sensor , I changed it and MAF sensor I change it too , but he said maybe the new MAF has a problem and try another one ? what do u think ? do u suggest me to go to the Mazda dealership ? and buy another MAF ?
Whats air straighter ? I think there is no leaking and air goes through MAF sensor and no air entering the system ... the car drives perfect and no problem but I wanna turn off the light and I wanna know the problem ....