zany tachometers

[rambus]

The tachs on my two 7.4 mercs show 1000 on port and 1500 on stbd when ignition is off...when started, the initial readings seem okay, then the needles will move up even though throttles are not advanced...same underway. I checked the guages for loose ground etc at panel...just weird that both act the same way...Anyone have an idea on where to start? Thanks

 

[makomark]

One 'quickie' fix that may help - spin the adjuster on the back several times across its entire sweep. reset it on "8 CYL" and see if that helps. If that doesn't help try these two items: verify the "Ground" at the panel is in fact solid all the way back to both the battery and the engine block - the other is to take the tachs (out of the dash) to an authorized shop. They will have a tach tester and can verify their operation and calibration.