164 malfunction narrowed down

[VLADDS@domain.elided]

My problem with the electrical cutoff is now a bit more clear as symptoms. I 
want to know if anyone feels it could be the rpm sensor. So, what I did so 
far was to replace the "engine relay' above the driver headlight. Replace the 
engine relay fuse , wrap the rpm sensor protective plastic sheet, where is 
was cracked with electric tape, checked the ground points on the passenger 
side of the intake plenum, and looked inside the socket of the rpm sensor.
What it does now is:
At rpm's over 2500 it will cut off the ignition and the tachometer goes to 
zero, and the check engine light comes on. Everything else electrical and 
gauge in the dashboard or anywhere stays on, is not cut off. The sequence 
described above lasts for half a second, then the engine goes back to 
running. This incident happens way more frequently at rpms over 2500 then 
under, and I think it doesn't happen under 2000 and never in idle.
Is this what normally happens when the rpm (crank) sensor goes? does it go 
bad gradually or does it go burnt suddainly?
The car disc doesn't list a code for the crank sensor, and my car keeps 
showing 4-4-4-4.
Is it possible the Motronic is defective?
Vlad
'91 164L
'85 Maserati Biturbo S

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