Jumping Tach on a Johnson Venom

[mittenbass]

I have a 1998 Johnson Venom 225. If you need the serial number I can get it but my boat is stored off-site so its not convenient.

Anyways, my OMC tachometer is not working properly. It reads correctly when the motor is running under 1500 rpms. Once the revs climb over 1500 rpms the needle drops to zero then returns to whatever speed I'm running at intermittently.

A little more background:

I experienced this problem last fall when I was running a 1995 Evinrude Intruder 150. This spring I re-powered with a remanufactured 1998 Johnson Venom 225 and still have the same problem. Accordingly, I wouldn't think its a part on the motor unless by chance the Venom happened to have the same defective part. However, the tach, controls, and associated wiring are the same from before (it all hooked up nicely to the Venom during the swap).

Lastly, I checked to make sure that the battery was fully charged, had clean connections, and was still hooked up with hex nuts and lock waskers (not wingnuts). My in-dash voltage gauge reads 14 when the motor is running and the voltage across the battery is 12.5 when the motor is shut-off.

Any help would be appreciated...was hoping the new motor was gonna take care of this problem. Thanks

[Cclutter1]

I have the same boat only a 200 venom on the back had the same tach prob earlier this year only mine went over 6000rpm and set off the rev limit alarm and then it just died. Your gauge should have the check engine alarms on it. Go to great lakes skipper. Com the gauge is going to cost around 68.00 $ that was the best price I found. Fixed my tach prob and other than having to tear the consol all the way apart it was pretty easy


Modified by Cclutter1 at 9:16 PM 6/15/2011

[mittenbass]

Okay, well this is starting to get frustrating. I bought a new tach and installed it today. Didn't fix the tach jumping/going to zero problem that I have. The tach is set to 6 pulses which I believe is where it ought to be.

Any other ideas as to what's wrong? Does this sound like a rectifier issue or something else? Any ways to test it out besides dropping another 80 bucks without fixing it I'm testing different props right now and its getting tough to gauge 6000 rpms by the seat of my pants . Thanks.

[mittenbass]

bump - I need help!!!

[ChampioNman]

Got a meter? Got a manual? There are tests in the manual for testing the tach. Seeing that the tach jumps with both motors I'd suspect something in the harness.

Seeing you went from a 1995 60* motor to a 1998 90* motor did you get an adapter cable to convert from the big red plug to the deutsh connectors or did you hack the harness to make it work?

[swat]

i just had a problem with my tach, was going from the correct rpm to zero, then back. found out that the ignition swith had a short in it.
i also had a problem several years ago on a stratos 285proxl- the problem then was a bad engine harness at the motor side by the plug it had the conversion kit on it. just something to look at. i found the harness problem at the boat launch by moving the engine harness while the engine was running just be careful.

[mittenbass]

Thanks for the responses.

ChampioNman - the mechanic who did the motor swap hacked the harness to make it work (or maybe not work ). Would you recommend replacing the harness or just having the wiring checked? If the harness should be replaced, ball park what do they run?

Thanks again.

[ChampioNman]

The harness is in the ~200.00 range. Good possiblilty that is where your issue is.