Yes, they are pressure driven. They sense the difference between the fuel system pressure and manifold pressure in my T model. So its not a direct measurement of flow. I think that a pressure fluctuation on the fuel side due to the influence of the heater is what I am seeing. Because I am running LOP, any fluctuation is noticable as a power change. If I was running ROP, I think it would be much less noticable. I have JPI unit with fuel flow meters as well. Its harder to see this kind of wobble on a digital readout. The one case where analog beats digital.
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