Tach question

[Saginaw Bay]

Ok,
I think I got a bad tach. It does not seem to register between 0 and say 1200 RPM.

I went today looking why.......
I found some loose wires, tightened them up, still same.

So I started grabbing,turning, and wiggling wires, nothing too serious, just trying to find a loose connection.

Bam, engine dies. and while dying, the tach maxed out.


I have hit waves and the boat dies, I think the jarring of the boat causes something in the tach to shut the boat off.


I have looked at the service manual, it shows 2 wires, but there are 4 on the back of the tach. I was thinking lighting, but it has a seperate bulb, Is the extra 2 wires power?

thanks

 

[cr2k]

Re: Tach question

Gray wire is signal from engine. Tach Terminal "S"
Purple wire is key switch power and my jump to other gauges. Tach Term "I"
Blue wire is for light and may jump to other gauges.
Black wire is ground and may jump to other gauges.
(These are standard wire colors, use these colors for comparison your mileage may vary.)

Also there is a switch on the back of the tach to select proper range.

Since you offered no information on what you are asking questions about I will guess....

Outboard the switch is for the number of poles in the charging system.
Inboard or I/O the switch if the number of cylinders your engine has.

Turn the switch back and forth and reset to correct position and see if this helps.

Usually a bad tach won't kill the engine but is it possible. Just unhook the gray wire and see if anything changes.

 

[jrampey]

Re: Tach question

Saginaw,

What engine/manufacturer are we looking at? My Mercruiser manual troubleshooting guide says a shorted tach or tach wire will kill the engine. removing the grey wire from the coil eliminates the tach and should allow the engine to start.

 

[jrampey]

Re: Tach question

Oops, I said that wrong... if its a recent mercruiser trace the grey wire from the 10 pin engine/instrument cluster connector and disconnect it from a terminal connector where it joins a grey wire coming from the engine control module... removing the grey wire from the coil will definitely keep the engine from starting! sorry.

 

[Saginaw Bay]

Re: Tach question

Its a '72 888 (302 V8)

I think that something must be amiss with the tach, as I stated after say 1200 RPM it works, but as I giggled wires when looking for a loose connection it maxed out the tach and killed the engine.4

and my thinking is: when in rough water say 2.5'-3' when the boat hits a wave hard, bam the engine goes dead.

I am thinking whatever I made mad in the tach tonight is the same thing as when I hit a wave.