1986 500SL KE system

Problem to solve: Engine looses power above 3000 rpm and will not exceed 3500
rpm.
In the remainder of this document this condition is referred to as “stall
condition”.
The engine starts fine hot or cold and idles ok.

Ignition:
Replaced the rotor and cap (new), tested the ignition wires, replaced the coil
and EZL with units from salvage yard (symptom did not change, so I assuming they
are in good condition). Measured voltage at ignition pickup (at flywheel) with
and it checks ok (possible that at higher rpm this might still fail). The ignition
timing is correct and the advance is working. Plugs clean and gaped. If the ignition
failed when the "stall condition" occurs the 02 sensor should go rich voltage, instead
it goes to a lean voltage.

Fuel system:
The “stall condition” is encounter with or without the EHA
connected, therefore the electrical inputs to the ECU are not causing the “stall
condition” Is this correct?
Replaced the FD with a used unit and encountered the same “stall condition”.
This does not eliminate the FD as the cause, but does increase the odds on it
not being the problem. Replaced intake manifold gaskets,the eight rubber coupling
rings and inspected all the remaining rubber idle tubes for crackes.
Fuel pumps have passed the fuel deliver (quantity) test.
F.D. upper pressure (at 80C) is 93.5 psi, lower pressure is 87 psi and gages
have been calibrated against each other.
These pressures remain constant up to and after the “stall condition”.
CO adjustment can be set for the 02 sensor to read .6v at idle, but any throttle
advance will result in 02 reading drop to .2V or lower depending on rpm. In “stall
condition” the 02 sensor reading jumps between .1V and .4v

Personal analysis: Suspect that the problem is fuel starvation, but don't know a
definitive test to prove starvation and the cause.

Anyone with an analysis?