My Faulty Ford MAP Sensor

Inside a MAP (Manifold Absolute Pressure) sensor from an old Ford.

In my case, a Ford Fairlane NL, March 1998.

This one 'works' but it's output frequency is about half what it should be: 89 Hz instead of 160 Hz. I can't explain why. It still works - frequency varies with pressure.

Manifold pressure is measured by a round transducer (middle of picture). It is about 10 mm diameter and contains a square plate covered by a semi-liquid jelly. Covering and connecting this sensor to an external pipe fitting is a rubber boot (as pictured).

To test, I applied 5 V DC and used an oscilloscope to measure peak-to-peak output voltage and frequency.

I measured 0.2 V DC to about 5 V DC, 88.8 Hz, 50% duty cycle.