PP Vacuum Gauge sending unit or not?

[Joey316g]

Where does the vacuum gauge in the PP car get its signal. I installed a Roush Phase 2 on my car and swapped in the ecoboost PP boost gauges and they work fine. Funny thing is I completely removed the entire induction system and never saw any MAP sensor or hoses that go anywhere to a hidden sensor. I'm a little curious. Maybe this has been answered but Ill be damned if i could find it.

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[engineermike]

The manifold pressure is inferred from other parameters by the PCM. The signal is serial (digital) communication to the gauge, not analog. In other words, the PCM sends the binary code for a number to the gauge and the gauge moves the needle to that number. The 5.0 PP gauge points to 0 at 0 or any pressure higher than that. I’m nearly certain that nearly all factory gauges work like that nowadays.

 

[Joey316g]

The manifold pressure is inferred from other parameters by the PCM. The signal is serial (digital) communication to the gauge, not analog. In other words, the PCM sends the binary code for a number to the gauge and the gauge moves the needle to that number. The 5.0 PP gauge points to 0 at 0 or any pressure higher than that. I’m nearly certain that nearly all factory gauges work like that nowadays.

Right.. I get that. What are the parameters that make up the algorithm

 

[Ruiner46]

Just a guess, but I think it is based on the inferred MAP signal the ECU generates from a speed density model. That model is probably based on the MAF, IAT sensors, and calculated volume of the intake, maybe throttle body opening, rpm, etc. If you dig in to the tune with something like HP Tuners, you will see tables for coefficients of a quadratic equation for a speed density model.

 

[engineermike]

Without having access to the code, I can only guess that the engine math model calculates the manifold pressure depending on all sorts of things like throttle angle, mass air flow, rpm, cam timing, etc.

Edit: ruiner ninja’d me.

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