Troubleshooting on tachometer

Hi All,

My 92 Four Winns with 5.8L OMC engine and Cobra outdrive was acting up yesterday. The tach is not showing the right rpm at idle and crusing. I used to get 700 rpm reading at idle but I get 1000 rpm yesterday. At crusing, I used to get 2500 rpm but it showed 3200 rpm. If I turn the engine off, the needle pointed at 300-600 rpm, once a while goes down to 100 rpm. Same inconsistancy apply when the key turns to start without cranking the engine.
Another potential problem is when I have cold start, there is a grinding noise then gradually goes away when the engine warms up. I can not pin point where it comes from but hope someone can give me tips to locate the cause so I can deal with it early. The boat is running well but I want do my best to keep it running.

Thanks for your input.

Frank

Re: Troubleshooting on tachometer

The tach is not showing the right rpm at idle and crusing.

Click to expand...

Ayuh,... If there's a Selector Switch on the back of the gauge, Turn to to, 'n fro, then back to where it belongs...
If that don't Fix it,...
Replace it....

Another potential problem is when I have cold start, there is a grinding noise then gradually goes away when the engine warms up.

Click to expand...

Is the starter Disengaging,..??

Re: Troubleshooting on tachometer

Thanks for the tip. I will give it a try.

The starter does disengage. The noise comes up when engine is cold, it goes away in a couple minutes. Is it possible that the altenator is about to go bad? Does a stethoscope help to locate which part is making the noise?

Thanks again,

Frank