1992 Ford F-150 4.9L – MAP Signal Stuck at 2.6V (Need Help Diagnosing)

Hello everyone,I’m working on a 1992 Ford F-150, 4.9L inline-six, EEC-IV (speed density) and I’m chasing down a drivability issue — major hesitation at wide open throttle.Here’s what I’ve tested so far:

• Using a Rotunda EEC-IV scanner and voltmeter.
• With key on/engine off, the MAP signal (Light Green/Black wire, PCM pin 45) reads ~2.6 V instead of the expected 4.5–5.0 V at atmospheric pressure.
• If I unplug the MAP sensor, the signal wire jumps to ~5.0 V (PCM bias looks correct).
• Tried 3 different MAP sensors (Motorcraft) — all give the same result.
• ECU has been repaired, but issue is unchanged.
• VREF (Brown/White) is steady at ~5.0 V.
• Ground (Black/White) is good — verified continuity to battery negative.
• Harness continuity from MAP connector to PCM pins checks out, no shorts found.

Conclusion so far:
It looks like the PCM’s MAP input circuit is loading the signal down, but before I write this off to another bad ECU I’d like a second set of eyes.Questions:

• Is there anything else in the circuit that could be pulling the MAP signal down to ~2.6 V with the sensor connected?
• Have others seen this failure pattern on these EEC-IV trucks?

Thanks in advance for your help!Danny

I haven't had to diagnose one of those, but according to service information, the MAP sensor is a frequency generator. Measuring voltage will not help.
KOEO @ sea level should be around 160hz and decrease with altitude.
KOER @ idle 92hz-to 112hz
The voltage you are measuring is an average voltage as the signal is being toggled high and low and likely won't change very much under most conditions.