1994 Ford Ranger 4.0 MAF Issues

[Braydencoc23]

I’m having Issues with my MAF system acting up, I have Code 157. I have a new a new Motorcraft OEM sensor, no intake system leaks, No vaccum leaks and a new PCM, but still having issues. I’ve been testing all the wires and getting 13.6 volts the red wire and 12.6 volts on the ground wire with key on engine off, but not finding any acceptable voltages or any helpful troubleshooting methods for the electrical side of this system any help would be appretiated

 

[RonD]

Welcome to TRS

157 Mass Air Flow(MAF) signal is/was low or grounded

Unplug the MAF sensor's 4 wire connector

Red and Black wires are for the Heater inside the MAF
Red wire should be 12volt(battery volts) key on engine OFF, use battery Ground or engine metal to test this wire
Black wire, test it using Battery Positive, should see same Battery volts, so its a good ground
That's it for those 2 wires, you can plug meter into both wires now, to confirm 12v(battery volts)

Tan/blue wire is also a Ground but for the sensor part
Test it like the black wire, to battery positive, should 12v, just like black wire

Now to test the actual signal back to computer
Its the blue/red wire
Plug connector back in
Start engine
Meter on Battery negative or good ground
Test voltage on blue/red wire, I use a sewing pin to pierce wires to test them when they are connected
Should see voltage that fluctuates slightly but usually about 1v
REV engine and voltage should go up
Repeat REVing a few times

If no voltage or no change in voltage then MAF sensor is bad or the wire back to computer is bad

 

[Braydencoc23]

Welcome to TRS

157 Mass Air Flow(MAF) signal is/was low or grounded

Unplug the MAF sensor's 4 wire connector

Red and Black wires are for the Heater inside the MAF
Red wire should be 12volt(battery volts) key on engine OFF, use battery Ground or engine metal to test this wire
Black wire, test it using Battery Positive, should see same Battery volts, so its a good ground
That's it for those 2 wires, you can plug meter into both wires now, to confirm 12v(battery volts)

Tan/blue wire is also a Ground but for the sensor part
Test it like the black wire, to battery positive, should 12v, just like black wire

Now to test the actual signal back to computer
Its the blue/red wire
Plug connector back in
Start engine
Meter on Battery negative or good ground
Test voltage on blue/red wire, I use a sewing pin to pierce wires to test them when they are connected
Should see voltage that fluctuates
REV engine and voltage should go up

Thanks for the welcome Ron!! So if the Boltage is higher on the red wire does that mean that there is a problem with the sensor? I tested the red wire with the engine on and it was at 14.6 and it didn’t seem right to me, but I will definitely be testing the signal wires to the PCM tomorrow. I had put a new PCM in cause the old one had corroded diodes but the problem has always occurred for years and had no change or luck in diagnosing it. Thanks for the reply Ron!

 

[2011Supercab]

So if the Boltage is higher on the red wire does that mean that there is a problem with the sensor? I tested the red wire with the engine on and it was at 14.6

He asked you to test with key ON and the engine OFF

 

[RonD]

+1 ^^^^

Battery voltage with engine running is 13.5v to 14.8volts
So yes, test with key on and engine off, just easier that way to test Heaters 12v and ground wires

 

[Braydencoc23]

+1 ^^^^

Battery voltage with engine running is 13.5v to 14.8volts
So yes, test with key on and engine off, just easier that way to test Heaters 12v and ground wires

So I have now tested both signal wires and the tan/blue was showing over 5 volts at idle and the blue/red showing .22 volts at idle so I decided to take the PCM out and inspect it just to be sure the diodes were intact and everything looked good so I will be tracing wires now.