RPM gauge trouble

[lug nut]

I have a 99 javelin venom with a 90 Johnson. My rpm gauge stopped working the end of last year. It will read between 500-700 rpm's and that's it. It will not even drop to zero when the ignition is turned off. If I tap on the glass the gauge will drop back down below zero then. I shot the wires and it seems I have power to the gauge, the 4 warning lights also work. I also followed the directions to troubleshoot the stator/rectifier as well. When I jumped the yellow/gray wire to the gray tach wire the tach. still did not work. I am thinking my tach. arm is broke internally due to the fact that its stuck and will not drop back to zero unless you tap it. Anyone ever had this problem? The gauge is a 7k Faria with a 8 pin connector on the back.

 

[boobie]

Re: RPM gauge trouble

From the sounds of it you have a bad tach as long as the charging system on the mtr checked out.

 

[lug nut]

Re: RPM gauge trouble

That is what I was guessing as well. The tach. will register when you turn on the key and then it will go between 5-700 rpm's at idle. When I turn the key back off it will just stay there even when I unplug the tach. I have to tap on the glass for it to go below zero...Looks like I will be ordering a new tach. this week. I'll let ya know if it fixes it.

 

[oldrudedude]

Re: RPM gauge trouble

I think the tach needle should go to zero when you turn on the ignition. When you start the engine the tach should read the rpm. When you turn off the ignition the needle doesn't have to drop to zero. As long as it goes to zero when you turn on the ignition the tach is probably ok. I just installed two new tachs on my boats. That is how they behave. Ignition on --> needle to zero. Ignition off --> needle floats.

 

[lug nut]

Re: RPM gauge trouble

Hmmm. My tach is doing just as you are saying Oldrudedude. It just wont go above 700 rpm's. I was tapping on it and it did go to a 1000 one time but that was it. I am second guessing myself now if it is the tach. Before the tach would not even register until I took it out and played around with it trying to find a problem. Could this be a sign of the rectifier going bad? I have no charging issues and I was getting plenty of volts to the purple power wire. The boat runs great and I have fished with it a few times now with no problems.

 

[oldrudedude]

Re: RPM gauge trouble

The tach should have nothing to do with the rectifier. The tach reads the A/C pulses from the alternator before it gets to the rectifier. If your battery is charging ok, the rectifier is probwbly good. If in doubt measure the D/C volts across the battery terminals when the motor is running. If the rectifier is bad the needle will jump all over the place. If the needle will not move past 1000rpm when the engine is obviously revving faster, it could be that the oil that lubes the tach needle pivot has dried up and the needle is being restricted by the hardened residue.

 

[lug nut]

Re: RPM gauge trouble

Thanks, I will measure the D/C current tom. The gauge did go bad after the boat sat for around 9 months while I was deployed. If the oil is dried up inside preventing the needle from moving, is there a way to lubricate it again? Or would I risk shorting it out?

 

[oldrudedude]

Re: RPM gauge trouble

The tach is probably not servicable. Probably have to destroy the bezel to get it apart. Too bad you don't live close to me. Local marine supply going out of business has a bin of new tachs for $15 each.

If it appears that the needle is sticking, maybe you could spray some WD-40 into the tach to see if it will loosen the needle up, if you can find a hole in the casing. If you determine that it is the tach that is the problem you have nothing to lose by doing that.

 

[lug nut]

Re: RPM gauge trouble

Well tried to clean the tach. up today. Sprayed some contact cleaner and some lube on the needle. Tach works now but it its working backwards. It will read zero and when I throttle up the tack will move counter clockwise to about 7k. It moves with the throttle now just backwards. Any ideas? I'm pretty sure this tach. is shot.

 

[boobie]

Re: RPM gauge trouble

It's shot.