1998 mariner mag efi - Erratic Tach

[4winnsskipper]

Ok my tach acts WEIRD. Plan and simple. Sometimes it works just fine (reads about what the engine sounds basically) but sometimes it will randomly jump around. For instance, i've started the motor once, motor was idling normally, and the tach read 3,500 steady. It was obviously NOT anywhere near that, more like the normal idle of 700 or so. Then sometimes at WOT the tach will peg, then drop back down to normal WOT range which is like 5,200 RPMS i beleive off the top of my head..motor sounds like it always has at wot and was NOT jumping around like the guage was.. So basically either the guage itself is shot or the "sender" is shot. But no clue where to start.

Motor 1998 mariner mag efi. 150hp.

 

[j_martin]

Re: 1998 mariner mag efi - Erratic Tach

Ok my tach acts WEIRD. Plan and simple. Sometimes it works just fine (reads about what the engine sounds basically) but sometimes it will randomly jump around. For instance, i've started the motor once, motor was idling normally, and the tach read 3,500 steady. It was obviously NOT anywhere near that, more like the normal idle of 700 or so. Then sometimes at WOT the tach will peg, then drop back down to normal WOT range which is like 5,200 RPMS i beleive off the top of my head..motor sounds like it always has at wot and was NOT jumping around like the guage was.. So basically either the guage itself is shot or the "sender" is shot. But no clue where to start.

Motor 1998 mariner mag efi. 150hp.

The "sender" is the stator and voltage regulator. The Tachometer is basically a pulse shaper and pulse counter. The extra pulses are most likely from a loose noisy connection, and could be either inside or outside the tachometer itself.

 

[4winnsskipper]

Re: 1998 mariner mag efi - Erratic Tach

The "sender" is the stator and voltage regulator. The Tachometer is basically a pulse shaper and pulse counter. The extra pulses are most likely from a loose noisy connection, and could be either inside or outside the tachometer itself.

so i should look where the wires connect to the tach itself first?