2111 code on 97 5ktq

[Nate Stuart]

> Hello listers.......a question about code readings.
>
> 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.

Totally different 'sensors'. Your telemetry gets it's information from the
ECU actually. The 'RPM' sensor that the ECU is complaining about is the
one on the side of the block, right at the seam with the tranny on the
drivers side of the car. It counts the teeth on the flywheel as they wiz
by. There are two identical looking sensors, the RPM sensor is the
rearmost one. Chances are it's probably gotten weak with age and is in
need of replacement. It's kind of hit or miss with these things, and so
far I've had good luck just swapping in used ones from junkyards. But YMMV


> 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 believe the ECU only uses this 'RPM' signal to check for rapid changes
in RPM (before one cam rev is completed), though it may use it to tell
precisely what position the crank is in for ignition accuracy. I'm not
sure. The ecu actually tracks engine rotation from several places, first
the window in the hall sender lets the ecu know that a full 4 strokes has
completed and Cyl 1 is back at TDC, then it looks at the pin mounted on
the flywheel (this signal is picked up by the sensors right in front of
your bad RPM sensor). And 3rd, the ECU can count the teeth on the fly
wheel from the sensor you have that is failing. I think I got some of that
right, and with any luck others that can better explain the timing
references will chime in.

HTH!
-Nate
'89 90tq
www.newtsplace.com/90tq