Erratic Tach - Troubleshooting - VWDiesel.net The IDI, TDI, and mTDI source.

• Erratic Tach by Op-Ivy on 26 May, 2008 19:08
• My tachometer has been showing swinging rpms lately. They seem to correlate to the actual rpm of the engine. But it will bounce erratically around the actual rpm. It has progressively become worse and worse.
  
  I have already tightened the compressor belt and the alternator belt and my alternator is charging well.
  
  It seems to get worse the higher the engine temperature is.
  
  Does anyone have any idea on what could be causing this?
  
  
  
  Thanks, Matt
• #1 by zukgod1 on 27 May, 2008 09:29
• Quote from: "Op-Ivy"

  My tachometer has been showing swinging rpms lately. They seem to correlate to the actual rpm of the engine. But it will bounce erratically around the actual rpm. It has progressively become worse and worse.
  
  I have already tightened the compressor belt and the alternator belt and my alternator is charging well.
  
  It seems to get worse the higher the engine temperature is.
  
  Does anyone have any idea on what could be causing this?
  
  
  
  Thanks, Matt

  
  
  Spounds like the alt may be getting ready to stop on ya..
  
  How old is it?
• #2 by Op-Ivy on 27 May, 2008 22:33
• It's 466,000km old, but was rebuilt a year ago or so. New bearings and new brushes.
  
  What kind of voltage reading should I be getting off the W signal?