Tachometer reading too high after having dash off to clean water pressure tubing.

[aanelso1]

I own a 2011 921 ProXP with 2011 Mercury ProXS 250.

The water pump was in need to be changed, so took care of that without any issue. Had a tournament and it worked well for most of the day. Late in the day, pump pressure on the gauge went way down and noticed very little "pee" stream from the motor. There were no warnings, but since we were close to the ramp, decided to keep speed and rpm's down and trailer.

Got it home, took lower unit off and checked pump, everything looked good. I did find a small piece of gravel in the tattle tale "pee" hole. Removed it and ran the motor on muffs getting good stream and no alarms. Pressure still would not come up on gauge, even while bringing throttle position up. I took the dash off and located the pressure sensor, removed the tubing and sent 20psi of air from the motor side up through the gauge. A muddy mess shot through (my wife was holding that end!....uh, oh!). Anyway, got everything working on that side after a good cleaning of the pressure sensor and the tubing.

Went to lake today, and everything seemed to work fine, except the analog tachometer reading is way off (my boat is not equipped with Smartcraft or MercMonitor gauge). I was pegging 7000 while running about 45 mph. I know this is not right! Is there some chance that maybe something on it got bumped into and incorrect switch position while having the dash off? I checked for the PIN settings, but could not find any information.


I appreciate any and all suggestions.

[RockYScouT]

There is a rotating switch on the back of the tach that sets for different engine cylinder configurations. It probably got turned.

[aanelso1]

My tachometer / water pressure / trim gauge has a DIP PIN switch on the back. There is not a rotating switch.

1 2 3 4 5 6 7 8
up up up dn up up dn dn

[WDEBass]

My tachometer / water pressure / trim gauge has a DIP PIN switch on the back. There is not a rotating switch.

1 2 3 4 5 6 7 8
up up up dn up up dn dn

it should be number 4 open all the rest closed, open is down and looking at the picture your number for us not all the way down.

[aanelso1]

I saw that from the magnified picture that I posted. Also, did check it and you are correct....it was basically "half way".

Thanks for the input! Heading to the lake to make sure it's working again!

Anybody know what the 7 & 8 PIN's are for?

[aanelso1]

WDEBass, your diagnosis was spot on. I actually only change #4 to Open....left 7 & 8 as it was. Still didn't work properly, and the WP gauge wasn't working. Changed 7 & 8 to closed, only 4 to open and everything is working again! Thanks again for the help!

BBC, thanks for a great forum to share information. Your site rocks!