Tachometer reads zero

[Glen Davis]

My friend has a 231. It has an analog tachometer, as well as a JPI 830. When he brings the power all the way back to idle, the JPI shows an “X” , meaning no reading yet the mechanical tach reads 800 RPM. Why would the JPI do this?

[carusoam]

JPI sensor is on the mag… picking up an RF frequency…

As the RPM drops, that signal probably gets weaker…

Probably want to check the sensor mounting to see if it isn’t properly mounted any longer…

Check the JPI data to see if any plugs start skipping as well…  If the mag is dying, it may have difficulty producing the rpm signal…

 

PP guessing only, no JPI sensor experience in my tool box…

Best regards,

-a-

[Fly Boomer]

6 hours ago, Glen Davis said:

My friend has a 231. It has an analog tachometer, as well as a JPI 830. When he brings the power all the way back to idle, the JPI shows an “X” , meaning no reading yet the mechanical tach reads 800 RPM. Why would the JPI do this?

When a gauge gives us a reading that doesn't sound right during runup (like zero oil pressure), we frequently start trying to determine why we have no oil pressure.  But frequently it's an erroneous indication, and we need to look at the sender.  In this case, you already have a couple of indicators giving you a second opinion -- the engine is obviously running, and the original tachometer says 800.  So, as @carusoam points out, its probably the gizmo sending the signal to the JPI.