1991 5.0LX TB4 tach (rpm indication)

[DrD]

Last time out my Mercruiser sometimes changed indication (to higher) rpm, even though the engine had not really changed rpm. I haven't started checking things for why this might be, yet; but was hoping someone on this forum might have experienced something similar and can suggest why this might be so.

Since this is an older boat, it might just be the tach gauge is sticky and needs to be replaced, or lubed(?) if it is possible to dissect it. I dunno ... help is appreciated.

-Dale-

 

[John_S]

Re: 1991 5.0LX TB4 tach (rpm indication)

It is common for boat tach to mis-read, especially on the high side. Sometimes tapping the faceplate and needle will drop. Other times it just goes away. Electrical noise sometimes get picked-up on the wire, and tach see extra pulses.

 

[getinmerry]

Re: 1991 5.0LX TB4 tach (rpm indication)

I've had this same problem on my old Glastron. On the back of the tach is a switch or knob with 4-6-8 on it. Make sure the switch is set to the right number of cylinders (for you it's 8). If it's correct, move the switch or knob back and forth a few times to possibly make a better contact...it might be a little corroded internally.

Chuck