Dead 3gm30f Tachometer

[George H260]

Can anyone tell me how to determine if my Tachometer is dead?I see there are four wires going to the tac. Red/black and black are the plus and neg wires. The orange and blue/red are the signal wires. Its easy to check the +/- but what type of signal should I be getting from the signal? voltage? ohms? Any one know?Also, does anyone have a good wiring diagram for the instrument panel? I have the manual and I'm not sure if it has one in it (will check next weekend). I would really like the harness diagram for the panel. I have the most basic one, tach, idiot lights, buzzer, light switch and key.ThanksGeorge S/V Windswept _/)

 

[ross]

the signal for

the tach is either an AC or squarewave DC signal. Attatch a voltmeter to the signal leads and you should see a pulsing voltage at cranking speed. The signal will probably be too fast to see at idling or running speed unless you used an oscilloscope to read it, but you should see a steady fluctuation at cranking speeds with a good meter.

 

[Fred Ficarra]

Before you get involved in fancy testing, George,

These tachs usually act up because of a bad connection at the sending unit. Look at the wires and make sure they are properly connected. The sender is 'hall effect' so it doesn't matter which wire goes to which terminal.

 

[Pops]

Hall effect

If you had a high school text book in physics or Google you could study up on the "Hall effect". Fred actually met Hall one day. He thought it was Jay Leno.

 

[Fred Ficarra]

Huh?

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/hall.html

 

[Dave Winiker]

Dead Tach

I'm also experiencing a dead tachometer on my '87 H31. The original engine manual fails to provide the location of the tach rpm sensing unit and I've not been able to find it it. Anyone know where its located on the 2 GM20?

 

[Fred Ficarra]

Dave, they are on the ring gear plane of the

flywheel. Look just behind the head on the bellhousing.