Boat I/O Tachometer problem

[cdpsrjc]

Please help me troubleshoot:



I have a Volvo Penta 5. 7L I/O and the tach is giving me problems. When I turn on the ignition, (motor not started) the tachometer pointer climbs and tops out. When I start the engine, the needle stays pegged. I'm not sure where to start troubleshooting. Any ideas? It;s basically A 350 V8 with electronic ignition, a coil, and 4V carb. '97 model.



Thanks for any advice,

Richard

 

[Shovelhead]

Is it a mechanical, or electric tach?

If mech. it sounds like the cable may be toast.



If electrical..... bad ground????

 

[cdpsrjc]

Shovelhead,



It's electrical. Any way to deternine where the ground problem may be? I really have no idea how an electrical tach works. I don't want to take it to a MARINE stealer.



Richard

 

[docdyno]

Tach malfunction diagnostic tip

Bad ground is a good place to start since most of these systems are electric tach equipped. Typically the tach takes a pulse signal from the distributor coil terminal. The ignition system functions as a switch to ground- thereby switch/grounding the ignition system through the distributor housing. The majority of the ground contact is made through the distributor hold-down. Remember the distributor base rides on a gasket (this is not really a great ground). Typically corrosion in this area will cause the problem. Weak contact point spring (if this one has points) or open or poorly grounded ignition control module will also cause this problem. Odly enough the engine may run OK, or have a slight high speed miss. This is a fairly frequent occurance. Verify grounds first both at the distributor and under the dash at the tach.

 

[TORQUE THIS]

What kind of boat?? Is the dash indivudial gauges or in one complete cluster like an auto??



I have a FourWinns and always have trouble with the dash. It looks like an automotive dash. It is also made for FourWinns by VDO.

 

[cdpsrjc]

Torque This,



The boat is a '97 Larson 226LXi. The inst panel is made up of individual Faria guages: MPH, Tach, oil pressure, amps, water temp,engine hours and trim setting. The tach is the only guage giving problems. I plan to work on it this evening looking for a ground problem. Thanks everyone for the input. This tach thing is driving me crazy(er).



Richard

 

[cdpsrjc]

Well... . It's fixed. Thanks to all who responded. A big thanks to docdyno who explained the system to me. The ground lug on the tach was loose (well, not loose, but just not tight enough for a good ground).



Lake ready and everything works now. Oo.



Richard