Code P0171 Lean bank 1

[Chunk61]

I have 98 Chevy C35000 Crewcab. It pulled the code P0171. With out really researching the code I replaced the O2 sensor. No good. After a little bit of research I cleanded to Mass air flow sensor. I cleared the code and it went 188 miles before it pulled the code again. 50 miles later the code cleared its self. When it first pull the code the MPG went down to 6mpg after cleaning the MAF it went up to 9.5.mpg. should the MAF be replaces? Any suggestions on aftermarket MAF's. Are they worth it. It looks to me that I can buy aftermarket for the same price as a Stock unit.

[maxwedge]

You really should do a full scan and look at MAF activity, baro sensor readings and fuel trims for a proper diagnosis

[777stickman]

Looking at my '98 C/K manual for that code there is no mention of replacing the MAF. The most common causes according to the manual are vacuum leaks, exhaust leaks and injectors running lean on that bank which is the drivers side. Maybe when you took the MAF out and cleaned it you sealed up a downstream vacuum leak??

[utoutlaw8]

My 99 Z71 did the same thing. Replaced the fuel filter and everythings fine now.

[Chunk61]

Thanks For the Info. I had replaced the Fuel Filter. No Luck there, that was my first thought. Some of the diagnostic checks that were mentioned I'm not sure how to preform. I'm using a ObdII code reader made By Actron model number CP9135. I just got back form Louisville Ky. and the truck showed no codes and I went @150 miles and averaged 9.5 MPG.

[98vert6spd]

id bet that you have a leak somewhere in the intake filter tubing

on my 98 corvette i had a small leak where the plastic houseing hadnt seated correctly with the maf and i got the lean code

its because the maf isnt registering much air so it isnt dumping in much fuel which is triggering the code

make sure everything is sealed up really well

if its not that then I would say you have an injetor going out.
I would doubt the injector because you would likely have a misfire i suspect

[MHardee]

Originally Posted by maxwedge

You really should do a full scan and look at MAF activity, baro sensor readings and fuel trims for a proper diagnosis

Check the Fuel Pressure Regulator...

[Sonny01]

Don't buy an aftermarket MAF...they are basically the same as stock without a screen. I took the screen off mine eons ago and the truck runs just fine.