Tach not accurate

[Redline54]

I recently bought a boat with a 5.0L Mercruiser and the tach is not accurate. The motor is supposed to top out at 4600 or so and the tach has me crusing at 6000. Based on the sound of the motor it certainly isn't running that high. What would cause the reading to be off?

Thanks,
Chris

 

[Bondo]

Re: Tach not accurate

Ayuh,... Check the Switch on the back of the gauge...
If that don't fix it,... Replace it...

 

[Redline54]

Re: Tach not accurate

It was actually just replaced because the old tach died. After the shop put it in it still gave no rpm indication, and then they pulled it apart and made "an adjustment". What adjustment is there on a tach to make, and what does the switch do you mentioned?

Thanks,
Chris

 

[Bondo]

Re: Tach not accurate

What adjustment is there on a tach to make, and what does the switch do you mentioned?

Ayuh,... The Question is your Answer dude....

 

[bruceb58]

Re: Tach not accurate

The switch is to select how many cylinders your engine has. For example, if the switch was set at 6 instead of 8, your tach would read 4500 instead of 6000.

 

[Redline54]

Re: Tach not accurate

I will check that switch, thanks.

 

[Expidia]

Re: Tach not accurate

Too bad you received a smart @ss answer to an honest question But hey, that's how you pad up to 27,000 posts I guess!

I'm going through the same thing as my new tach is coming next week.

How would anyone know that there is a dial or switch on the back of an already "installed" tach because how can one fit their head behind the dash to see a switch on the back.

Sounds like they left it on the wrong pulse setting to match your stator or alternator. Just try each of the several positions until it reads your idle around 800-1000.

Note: some tachs have dip switches that look like this:
http://www.beede.com/Techdocs/54631402.pdf

Below is an excerpt from a thread from a very helpful poster:

April 15th, 2010, 05:39 PM
Joe Reeves
Admiral
Join Date: Feb 2002
Location: Central West Florida
Posts: 6,755

Re: Wiring A tach

--------------------------------------------------------------------------------

The engine (1985 60hp Evinrude) is "Tachometer Ready". You simply need a tachometer that can be adjusted to receive six (6) pulses. The usual tachometer has a dial on the back of it whereas you simply set the dial to number 6.

The usual tachometer will have four (4) wires.

Gray (sensor) connects to another Gray wire that will be protruding out of the engine to instrument or control box wiring harness.

Purple (voltage) will connect to the "A" terminal of the ignition switch.

Black (ground) will connect to a black related battery ground.

Blue (light) will connect to the proper terminal of the light switch.

Normally there will also be a three (3) prong rubber connector under the ignition switch if using a regular typr Evinrude control box..... or the plug may simply be hanging out the end of the wiring harness if a console type control. This plug will contain the Purple (voltage), Gray (sensor), and Black (ground) wire.