Fuel Gauge, Tachometer, Speedometer ??

[milmat1]

None of the gauges work in the old boat. It's a 86 Subird Bowrider W/88hp Jihnson BTW.

Can someone explain the basics of how these gauges work? And how to troubleshoot them??

The Speedo I think I understand, It may just need the Plastic piece that rides in the water and Maybe even a hose. But it operates on simple pressure....

The Fuel gauge : How does this work, I understand theres a Sending unit in the tank and the actual gauge, Is the sending unit a Float type Resistance unit ?? And the Gauge simply a Small Ammeter ??



The Tach: I would really like to have the Tach ! Anyone know how it operates on the Johnson OB ?? I have seen post referring to the Rectifier, Is that part of the tach operation ??

Any info or suggestions would be appreciated as I'm going to tackle these this weekend...

This boat has made my motorcycle Extremely Jealous !......

 

[Silvertip]

Re: Fuel Gauge, Tachometer, Speedometer ??

You apparently missed the "Electrical" forum.

Speedometer: Non-electric. Pitot driven which is either a separate device mounted on the stern and hanging into the water or it is built into the lower unit of many larger outboards. A small diameter tube goes forward to the speedo head. Water pressure compresses air in the tube -- a bourdon tube in the head expands causing the needle to move.

Tachometer: Electronic. Requires +12 volts with key on, ground, and a sense (pulse) signal from the charging system. If you look at the control box just under the key, you will see a three terminal connector. Guess what that's for.

Fuel Gauge: Electric -- requires +12 volts when the key is on, ground, and a connection from the "S" (send) terminal on the gauge to the sender in the tank. Yes -- the sender is generally a float that swings an arm that moves a variable resistor. 240 ohms = empty, 109 ohms (nominally) = 1/2 tank and 33 ohms = full. Here is a diagram (again).

For the tach and fuel gauge, check for +12 volts (key on) and ground. For the fuel gauge you can check the sender by disconnecting the sender lead and measuring resistance. Values are above. The shell of the sender must also be grounded or the gauge will not function.

 

[milmat1]

Re: Fuel Gauge, Tachometer, Speedometer ??

Great Info !!

Thanks !!!

 

[milmat1]

Re: Fuel Gauge, Tachometer, Speedometer ??

Well,The Speedo worked by blowing in the hose at the back, But the plastic piece that holds it in the water is broken.. So I'll fetch a new one from Fleabay..

The Rectifier is good, (Suprised!) So the tach or wiring is hosed up, Likely the wiring because it was a total MESS Anyway !

The fuel meter must be good because when I turn the key on it swings all the way to full then back to E.. Sometimes at random it will flicker back and forth. So I am again thinking WIRING, or maybe the tank sending unti. I can find a way to get to it without cutting a giant hole in the boat though....

SHEEWWW Does it ever End ??

 

[seabob4]

Re: Fuel Gauge, Tachometer, Speedometer ??

Sounds like you have a ground issue with your sender. Check for continuity on the ground from your sender to a known "good" ground, and from your gauge also.

On your tach, the purple wire from the engine harness goes to "I", the gray wire to "S", and, of course, the black wire to "G"...