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Air/Fuel Ratio Problem


Singlalt

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I have a 2002 Ford Ranger Edge, and I haven't had a problem with it. Then, the other day I get in it and I notice that it's not idling smooth. Once I put it in gear, I notice that it seems to be running at a higher RPM than normal. Finally, it throws an error code which I check and find that its code P1121 which apparently is "Throttle Position Sensor Inconsistent with Mass Air Flow Sensor".

Ford offers the following 4 options for this issue:
  • Air leak between Mass Air Flow sensor and throttle body
  • Faulty Throttle Position Sensor
  • Throttle Position Sensor harness is open or shorted
  • Throttle Position Sensor circuit poor electrical connection
  • Damaged Mass Air Flow sensor
My first thought was to try to clean the MAF sensor, so I got me a can of MAF cleaner. I clean it out good, but nothing changes. I then checked the voltages on the TPS. I found that at rest, the signal wire read 0.95V, and as someone slowly depressed the accelerator, the voltage rose to 4.55V, with no noticeable gaps.

Someone also suggested that I check for a vacuum leak, so while the engine was running, I unplugged the IAC valve. Immediately, the RPMs dropped to nothing.

I cannot find a leak in the air handler piping between the MAF and TPS. At this point, I'm not sure what else to look at on it. Is there a way to check the functionality of the MAF?

I'm open to any suggestions and help. I appreciate any and all advice.
 


RonD

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Welcome to TRS :)

Yes, you can test MAF sensor with Volt meter like the TPS.

Use sewing needles to pierce wires

Look here: https://therangerstation.com/tech_library/CleanMAF.shtml

About 1/2 way down is Testing

MAF is heated so has a 12v(red) and Ground(black) wires for the heater inside
Other 2 wires are for the sensor, a Tan and Light Blue wire, test these at warm engine idle, lower voltage with lower RPM, higher voltage with higher RPM, it uses a 5volt range like the TPS sensor
At 800rpm I would expect about .6v on a 3 liter engine
MAF voltage tops out at about 3.5v

MAF sensor is measuring the WEIGHT of the incoming air more than the flow, computer already "knows" how much air a 3 Liter engine will use at any RPM and throttle position, its just math, which is what the computer is good at
What computer doesn't know is the WEIGHT of that in coming air, i.e. sea level air weighs more than air at 3,000ft elevation, and Cold air weighs more than hot air, "hot air rises", because its lighter than cold air

And air/fuel ratios are WEIGHT ratios, not volume
14.7/1 gasoline ratio means 14.7 POUNDS of air to 1 POUND of gasoline, or 14.7 grams of air to 1 gram of gasoline
So there is no EXACT MAF voltage for RPM with a 3.0l engine, because it will change based on air temp and elevation


There are some 6 wire MAF sensors, ignore the outside 2 wires, they were added for an Air Temp sensor
 
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Singlalt

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It's good to be here.

I appreciate the help. I finally got back around to fooling with it. I got 12V on the hot wire, as expected.

On the light blue I got 0.8V at idle, and as the engine was revved, that rose to about 2V at around 2,500 RPMs. It probably would have went higher, but I didn't want to rev it much higher at the time.

On the tan wire, I never got much more than 0.18V. I even reset the needle to make sure it was seated properly, but I got the same thing everytime. Is that normal for a MAF that is malfunctioning, or is there some user error?
 

RonD

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Yes the Tan wire is in essence a Reference Ground so should be close to 0volts and not vary
Blue wire is the "signal" the computer uses, so volrage should go up with air fklow/RPMs

Test seems to show MAF is OK
 

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