Tach jumping

[black pearl]

Sitting at the dock engines at idle, and the port side tach is jumping from 800 rpm's to all the sudden 3000 rpm's then 1800 rpm's then back to 800. So I thump on the tach meter and it starts jumping again. Finally it goes back down to 800 and stays there. This has to be a cable problem. I was thinking of removing the panel and spraying wd40 into the cable. It has been doing this all year but seems to be getting worse as time goes on. Besides replaceing the cable any other idea's? Thanks Jim

 

[Presentation]

Sitting at the dock engines at idle, and the port side tach is jumping from 800 rpm's to all the sudden 3000 rpm's then 1800 rpm's then back to 800. So I thump on the tach meter and it starts jumping again. Finally it goes back down to 800 and stays there. This has to be a cable problem. I was thinking of removing the panel and spraying wd40 into the cable. It has been doing this all year but seems to be getting worse as time goes on. Besides replaceing the cable any other idea's? Thanks Jim

Remove the tach

On the back, with a very small screwdriver or some other small thing, flip that little switch back and forth between V8 V6 and V4 a dozen times. Flip it back to V8, reinstall.

 

[bluebelly]

Sporadic readings from the tach usually indicate that your ground wire that is attached to the back of the tach is not making a good connection. Cleaning the contacts and then applying dielectric grease should fix it. My 95 290 had this problem about every 2 years. I discovered that the back of the gauges were getting wet every time I washed the cockpit out. I finally used a caulk to seal the perimeter of the faux wood panel that the gauges were mounted to and the screw holes to try to keep out moisture. It seemed to work.

 

[Uplate]

Remove the tach

On the back, with a very small screwdriver or some other small thing, flip that little switch back and forth between V8 V6 and V4 a dozen times. Flip it back to V8, reinstall.

there is also an electronics/contact cleaner called Blue Shower that you can spray on all electronic components to clean.

Corrusion is probably not going to be cleaned by anything other than a new gauge. I will probably strat replacing my guages soon as they are not accurate anymore.

Mike