tach voltage at idle

[hullofalottatrouble]

have a 1982 mercruiser 260 with 260 drive..<br /><br />so here is my quetion.. the tach doesnt work.. so i tested the voltage from snd to gnd at i get like 8.4 at idle.. it does up when i throttle up just as it should.<br /><br />but without a tach cant i tell the rpms from the voltage? seems to me thats all the tach does.. <br /><br />so if that is the case.. what kind of voltage should i expect at idle?<br /><br />thanks

 

[hullofalottatrouble]

Re: tach voltage at idle

i have the original medallion tach now that does not work.. just in case anyone was curious..

 

[hullofalottatrouble]

Re: tach voltage at idle

here is the question.. all the tach does is give a reading as a response to the voltage no? so if that is the case do all tachs respond to the same voltage in the same way?<br /><br />if so cant i just read the voltage? And if so what would be the voltage at say 600 rpm?

 

[Dunaruna]

Re: tach voltage at idle

The circuitry inside the tach converts pulses from the ignition coil into voltage which in turn moves the needle, measuring the voltage on the sender terminal will tell you nothing.<br /><br />Turn your ignition on, measure between purple (12v ignition) and black (ground). You should see battery voltage. If not, you've got a 12v ignition feed problem.<br /><br />Measure the resistance between the negative coil terminal and the sender terminal on the back of the tach, you're checking to see if you have a broken wire. <br /><br />If both these tests are o/k, you're tach's faulty.<br /><br />Aldo