Troubleshooting sync and tach gauges

[Z-Worthy]

My port tach on our 1997 400DA with CATs is bad. I think it reads accurately sometimes, but other times it just jumps around. When it settles down and stays in one spot for a few minutes, I trust it. However, even when I believe it's reading correctly and both tachs are the same, the sync gauge is usually still hard over to starboard. So I'm pretty sure BOTH gauges are bad (or worse, a bad tach and a bad sync module). I spent a while last summer centering my rudders, setting my starboard RPMs, then slowly adjusting my port until I could hold a straight course. Using that method, I was pretty sure the engines were spinning closely (completely ignoring the port tach). But even then, the sync gauge was usually over to starboard.

First and foremost; new Aetnas are not in the boat budget this year. I came close, but decided to shift those funds to new canvas. So I'm stuck working with what I have for another year. It's not a huge problem because the boat still runs like a dream. I just hate having to "guess" what my port RPMs are by using the pitch of the turbo and a bad tach.

My question is: what is the best way to troubleshoot this situation? Swap tachs from port from starboard and see if the problem moves with the gauge? Could the bad tach be throwing off the sync, or are those unrelated? Any suggestions are appreciated.

 

[Lazy Daze]

Swapping gauges is good idea. Before you do that, though, you might get lucky and just have loose/dirty connections on the backside. Anytime I see issues like what you are experiencing, that's usually the first thing I think of. Remove connections, clean (get a cheap, little brass brush), reinstall and cross fingers. You can get these little brushes (the brush part is only about an inch long) for just a couple bucks at hardware stores or even a place like Harbor Freight. It might turn out to be something else, but this is at least relatively easy and (just about) free. Besides, it's good idea to do this every so often anyways. As far as protecting the connections from further corrosion, the best thing I have found is a product called Tef-gel.

 

[fwebster]

Sea Ray used Teleflex tachs on your boat. The diesel tachs use a tooth counter on the flywheel for the tach signal. Some gas boat have tachs with switches on the back to set the number of cylinders on the engine, but yours does not. The back of the tach is sealed and there is nothing user serviceable inside. Your description is that typically seen with a Teleflex tach that is bad. You can bang on the face for a time, but sooner or later, it isn't going to function reliably. Unfortunately, the only options is to replace it. So this boils down to your spending $225(est.) for a Teleflex from your Sea Ray dealer for a tach that is going to fail in 4-5 years or $282.50 for digital Aetnas……..X2 plus whatever you decide to do to make the smaller Aetna's fit the panel.

I think the sync. gauge is a separated issue or is the result of it not getting a good signal from the harness behind the panel. Dennis's idea is worth trying because it is cheap and only costs you a Saturday morning to take the panel out and harness connectors apart.

 

[Z-Worthy]

Frank, I definitely think upgrading to Aetnas is the way to go. I even went so far as to try a few different methods for cutting custom bezel rings out of black acrylic sheet to make them fit the panel (side-note: cutting a perfect circle out of acrylic is a terrible project no matter how you try it). But the financial coordinator put the freeze on me after she found out how much I spent on canvas.