BW56

2004 V6 S10 Blazer threw the dreaded running lean codes. Auto Zone plugged in their scan tool and read the P0171 P0171 codes. The only thing on their suggested printout was a $85.00 plus MAF Air Flow sensor. Not sure that was the problem I looked closer. The internet said check the MAF first. Unpluged it, turned key to on position, found the hot 12 volt pin. Re installed and fired it up, found the signal return showing low voltage as it should. Revved it some and the voltage increased as it should. MAF sensor is good. Checked every vacuum hose and line looking for leaks while it was running. I used a squirt bottle with water, there are many ways to accomplish this. All intake gaskets and air intake hoses were good. Looked at all the vacuum hoses one by one working my way across the engine, passenger side first to the drivers side. FOUND TWO leaks. Both from the top back of the engine, side by side, one going to the drivers side valve cover, the other a smaller line going to a T between the fender and brake booster. $10 for the formed 90 and 1" of 5/16 and 15" of 7/32. Started it till it warmed up. Shut it down and disconnected the battery. waited five minutes. Put it back together and NO SERVICE ENGINE LIGHT. Not bad for a squirt bottle, cheap voltage meter, a few hours of work and research. P.S. This happened just before it has to be emissioned this month.

tech2

good find
easiest way to check for vacuum leaks is to let engine data tell you
if the fuel trim is adding (mt 10%) on both banks at idle but normal at 2500 rpm...you have a vacuum leak

BW56

P.S. I also had 60 psi from the fuel pump so it and filter were fine. Cars seem to have miles of vacuum lines these days so finding and checking them all is the biggest job. A smoker would have been a great help and next on my agenda if I hadn't found the leaks..