1998 Ford Explorer 6 cyl Four Wheel Drive Automatic 180000 miles
Check engine light is on because bank 1 and 2 are too lean. Testing the Mass Air Flow power source with the key turned in the on position, the voltage out put was 5 volts. The battery tested at 12 volts. The out put should read 10 volts or higher / close to the battery. What relay switch or fuse may affect the volts presented to the mass air flow sensor? I have not checked the wires for proper circuit out put.
Actually, let me explain the way it works. ALL computer sensors are supplied with what is called " voltage reference.&Quot; In order to prevent inacurate readings caused by voltage fluctuations at the higher voltage. The computer reduces the voltage to 5 volts. This is the standard " vref" signal supplied to engine sensors. It cannot be altered. However, when measuring the MAF, there are multiple wires. One is the vref, one is the ground and one is the signal wire that returns the signal to the computer. On the MAF sensor, there are also two other wires that measure barometric pressure. So when you are testing the MAF it should be tested when the engine is running and on the sig return wire. But if you have P0171, P0174 codes, they are lean codes and not MAF sensor codes. You should be looking for an intake leak. The codes are produced because there is a leak that is unmetered. It is allowing air to be sucked into the engine when it shouldn't be. Check the intake gaskets and vaccum hoses. Post back the results and we'll go from there.