RPM Gauge/Vibration/Depth finder problems
 

This website has been so informative for me in the past I thought I would post a few more questions and solicit everyone’s input. For this posting I have three questions regarding my 1991 Baja with twin 7.4 mercs and bravo 1 drives. I appreciate any help you can give.

First Question: My original RPM Faria gauges have some sort of electrical feedback in them. Upon turning the key the port RPM gauge will register 1200 RPM's without the engine even running, and will maintain the 1000-1200 difference when I start the motor. Port engine will read 2400 RPM while the starboard motor will read 1200 RPM. This offset will last for a while, then go away and return later. When this happens I run the boat off the SYNC gauge. The SYNC gauge is always right. I don't understand. Is it some type of sending unit on the distributor??? Or is it the gauges??? Why is the SYNC gauge always right? Troubleshoot?

Second question: I have a horrible vibration on the starboard motor at idle rpm's. The vibration is present whether I am in drive or in neutral. It goes away after I increase the rpm's. Is it the motor mounts? The Bravo drive? What is wrong?

Third Question: My Hummingbird depth finder is not working. I see the sensor in my bilge, and the gauge works, but gives false readings like when I am in 100 feet of water is will register 8 ft or some crazy number like that. How does someone trouble shoot a depth finder, or for that matter fix it????

Again, thanks in advance for your responses!

LL

about your gauges, your not running solid core plug wires are you? and your engine vibrations, the first thing i would check would be the big bolt on your harmonic balancer, then your engine mounts.
fran

Thanks excaleagle for the reply. I believe I am running solid core plug wires. What should change to?

As for the vibration, I will check the big bolt on the harmonic balancer.

Thanks again

LL

solid core wires can cause some electronics to act goofy, and can make a feedback noise in your stereo if it's on. they are mainly used for racing anymore. you could change to a carbon core. don't forget to check your front mounts as a nut could have easily backed off causing your vibration if the locking tang was never bent over.

Spiral core wires wont cause a problem on a non ECM motor. also I would lean more towards U joints and or gimbal bearing. Broken motor mounts shouldnt cause vibration in neutral and loose harmonic balancer would be very obvious and wouldn't last long.

Tinkerboat, you can always count on your informative response. I appreciate your input.

I really don't know what the vibration is. I am going to try everything.

As for the solid core wires.........something is causing my RPM gauge to read a false value and I don't know what it is.

As for the problem with the tach readings, I would first switch them from one engine to another. If the same guage still gives the 1200+ rpm reading on the other engine, then the guage is bad.