Class

My engine was throwing both P0171 and P0330 codes. I changed the spark plugs, and fingers crossed, the P0330 codes went away, the gas mileage improved, but the P0171 code keeps coming back. I cleaned off the mass air sensor with isoprophl alcohol. I don't think that helped.


The forums and internet seems to have a lot of advice on the P0171 codes, and point to several possible reasons. Because there are several possible answers, I was wondering if the air flow reading from the ECU helps to troubleshoot.

I'm using a bluetooth OBDII to android phone, and it has a display screen to read the quantity of air. At idle it might show 3.5 g/s (is that gallons per second??) And rises when the motor is under fast acceleration. If I've cleared the codes, the P0171 code likely comes back if I accelerate while going up hill.

Class

Wrote too soon, the P0171 code came back.

Typically the OBDII app shows something like 4.5 g/s at idle (3.4 -5.2) and up to 37 g/s while driving on the highway, with an median number near 20 g/2 on highway.

fastnoypi

if your maf is good, then the lean code would have been triggered by one of your forward o2 sensors. Make sure all the hoses are secured past your airbox to the throttle body so it eliminates the chance of unmetered air.

g/s is a measurement of grams/sec of air passed through your maf sensor.

salimshah

It is the neat chemistry at work in modern engines ..
x moles of oxygen would need y moles of fuel and that y moles of fuel are then allowed to enter
All this is termed "metering".

Salim

carguy07

I think a vacuum leak or cracked exhaust manifold will throw the code too,