Check engine alarm at start up

[javelin389b]

Turn the key on without cranking engine and it goes through the checks then the check engine light comes on and stays on without an alarm. When you crank the engine it goes through the checks and the light comes on and the alarm sounds for about 20 or 30 seconds solid beep. I can run the boat down the lake and the light will go off and everything is normal. Every once in a while the check engine light and alarm comes on while running W.O.T. but goes away and the engine never skips a beat. I know the check engine alarm is usually fuel restriction but I'm having the problem as soon as I start the engine. I`ve done some reading on here and read that it could be the tach has gone bad but before I start replacing things from me guessing I would like to know what you guys think.
Mod. #J150GLEDB

[ChampioNman]

Unplug the vacuum switch prior to starting the next time and see if it goes away.

[javelin389b]

Unplugged the vacuum switch and I still have the alarm.

[ChampioNman]

Unplug the rest of the tan wires on the motor, one on each head and the low oil and vro if equipped. Turn the key to on if it still alarms bad tach.

[javelin389b]

May be a dumb question but are the vro and the low oil the same plug?

[SEAHORSE]

If the gauge is original, it may be at fault as a constant CHECK ENGINE light is a common symptom if the engine checks out OK. Substituting a known good gauge is the easiest and quickest test.

[javelin389b]

Just wanted to give an update on this problem. Ordered a new tach and put it on today and no more check engine alarm. Thanks guys for the help.