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I read that the MAF sensor output voltage increases as RPM increases. The ECU uses this voltage to determine other things, like idle RPM, ignition timing, fuel injectors, etc. Where can I find the correlation formula or graph for particular vehicles like Ford E-150's?

Also, throttle position sensors work in the same way. They output a voltage to the ECU, and the ECU uses that voltage to determine many things. Since they are pretty much all electronic nowadays, where can I find the correlation formula of say, the throttle position sensor output voltage and ignition timing?

I know this might be a complicated question, so thanks for any help.

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I think you misunderstand the purpose of the Mass Air Flow (MAF) sensor (and whoever wrote what you read doesn't understand, as well). The purpose of the MAF is to read the amount of incoming air. As the incoming air flows over the heated sensor, it cools the sensor which regulates the amount of electricity which can flow through it. It is in no way associated with the RPM, nor does it read the RPM of the engine. The only way that an increase of RPM would affect the MAF output is because inherently there is more air going through the MAF when the RPM's increase. This is not a direct reading. If it were as you are suggesting, there wouldn't be a need for a Throttle Position Sensor (TPS).

Also, the ECU doesn't use the voltage of the MAF to determine the idle RPM. The ECU has a target idle RPM it tries to maintain by adjusting the timing, plotting the fuel injector pulse width against the fuel map, and adjusting the Idle Air Control (IAC) valve.

As far as any correlation formula or graph, there isn't going to be a set one. And Ford is going to maintain these as proprietary data. Each vehicle model is going to have a different one. You would have to take tuner software, read the tune for the specific vehicle you want to examine, then create the correlation from the data you extracted. Let's just call it reverse engineering. It would be a generous tuner who would put this information out there for common consumption.

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  • Thanks for the clear explanation. So the idle RPM, or the RPM at any speed, is not dependent of the MAF, right? Instead, the MAF reading is dependent of the RPM? On a side note, how many wires does a MAF usually have? I was working on a Ford and noticed that the MAF had 6 wires connected to it, 2 for +12V and GND, and I'm guessing 2 for the air mass reading. What about the last 2 wires? DO they read intake air temperature? I remember that the temperature sensor is often incorporated into the MAF sensor housing nowadays. Thanks for your help, Paulster2.
    – user3211857
    Dec 27, 2014 at 21:38
  • @user3211857 ... I would suspect it could be incorporated into the MAF. A common means is via a separate sensor which actually reads the temp. This is important to have so that the MAP (if so equipped) can read the air density (pressure) correctly. As far as the number of wires, I'm sure this is dependent upon the application. Manufacturers can do their own thing.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Dec 28, 2014 at 0:33

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