Tach off from sync

Jeff Delbuono

Jeff Delbuono

Well-Known Member
Jun 11, 2018
1,126
Edison New Jersey
Boat Info
1998 Sea Ray 290 Sundancer
Engines
5.0 efi w/ alpha 1 gen 2 drives
1998 290 Sundancer with twin 5.0 EFI and alpha 1 gen 2 drives.
Never had this before. So took the boat out this week on a flat bay day and throttled up to go on plane. after it lays down i normally pull back to like 3800 rpms and both motors sync up nice at 25 knots.

This last trip I planed off and when i pulled back i had to have the port at 4100 rpm and the starboard at 3800 rpm to have the sync in center. motors sounded strong and ran great and did not skip a beat. Should i go by RPM or by SYNC. Thoughts? have not taken out since that trip so not sure if it was just a fluke of something i need to address.
 
Sync is accurate, tap the tach next time if it’s still stuck they’re flaky
 
Its probably one of the tach's as Strecher said. You can try opening up the dash and cycling the 4-6-8 cylinder selector switch on the back. Others have said that can fix them from reading wrong. While you are back there you can check the wiring tightness.

Another potential is moisture in the tach. Try running with your nav lights on and dash dimmer set to full bright, so the tach lighting is on. The bulbs are incandescent and can dry out the inside of the tachs (just don't forget them on if you are using them in the daylight).
 
Our port side had some corrosion on the purple wire and caused all kinds of wackiness. I disconnected them and cleaned all the connections up and it’s been better but still a little erratic. I added the fox marine gateways and the analogs are off by 100-200 rpm
 
I have the same phenomenon but haven't opened up the dash to look at the wires or switch the settings back and fourth.

I just go by the sync gauge.
 
Understand this isn't a realistic (or cheap) fix but I really can't say enough about the Fox-Marine gateways if you have an NMEA plotter/display. I absolutely love the digital tach and temp readouts, and fuel flow is a big benefit
 
I have twin 8.1's and sometimes the tachs are in sync, sometimes they are not. I realized that the sync gauge is what I want to follow, and it always corresponds with the audible sync that you get when you're dialed in on both engines. You can hear and feel the boat happy when sync is right on the midline. It is annoying that sometimes my starboard tach is off, but it's a first world problem I think :)
 
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Tachs are off, but sync is engaged. The boat is running straight & true.(so I know the tach is the problem) What has been done in the past is to clean the contacts on the back of tachs and for my boat, there is wiring harness in the ER for each engine, it has a disconnect so I pulled it apart, cleaned the contacts and covered it in dielectric grease with good results. There is a fair amount of folks on the site that have replaced their stock tachs because SR didn't spend a lot of money on them...
 
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