2111 code on _87_ 5ktq

[Doyt W. Echelberger]

Hello listers.......a question about code readings.
(Er, Uh,,,,ignore that question about a 97 5ktq)

2111 indicates "RPM sensor signal not getting to Mac 11C ECU in my 87
5ktq."  Yet my speedometer and tachometer work just fine, as does the dash
computer.  I think suspect that each of these components depends on that
same RPM signal.   ....but maybe not.

If the above is true, and if my ECU isn't receiving an RPM signal, that
would indicate that the wire between the signal generator and the ECU is
broken.  (but not broken to other locations such as tachometer and dash
computer?)

Or, Do those components run off some other signal?

If all these components run off the same RPM sensor signal, and some of
them are getting that signal, then I can conclude that the RPM signal
generator (sensor) is functional and does not need replacing.  But I'm not
sure that they all run off the same sensor. That is my first
question.....do they?

My second question asks how the ECU _uses_ the RPM signal. Does the RPM
signal have anything to do with the way the ECU handles starting, or how it
adjusts timing or fuel delivery or boost?

I've studied Bentley on this, and need a little reassurance about the above
details.

Doyt Echelberger
87 5ktq in OHIO   USA