Offshoreonly.com - tachometer goes crazy after 4000 rpms

Quote:

Originally Posted by JCG (Post 3494546)

I have the same problem!..
My boat originally had the Thunder IV ignition, in tandem with an MSD. The MSD failed so we bypassed it to use only the Mercruiser Thunder IV. Ever since this bypass, my tach goes crazy over 4K rpm, just like yours. Let us know if you find the problem.

Thanks!

Julian

Hey Julian, Just found the problem today,My mechanic Bob found a feed wire that goes from the ignition switch to power the port side of the dash that was loose, so the port side was not getting 12 volts ,instead the voltage would decrease. Who would ever think this could be so simple. We changed both ingnition modules inside the distributors thinking that might be the problem because mercury up graded this system a few years back and these had not been upgraded. Any way you might want to check your wires from the ignition to make sure the connections are ok. Good luck Gregg