What Is My Tach Saying To Me?

[Salty Tricks]

While my engine is on earmuffs I raised the RPM just slightly and I can see the tachometer needle drops off as soon as I reach 2K (actually zeroes out). Is this indicating a problem with my ignition systems?

 

[Joe Reeves]

Re: What Is My Tach Saying To Me?

No, it's indicating a problem with either your tachometer itself or the charging system.

 

[Salty Tricks]

Re: What Is My Tach Saying To Me?

Thanks Joe<br /><br />I guess that means rectifier, stator? Is my rectifier a watercooled unit? My manual doesn't describe it but I am assuming it is. 1985 90hp V4 Johnson w TandT

 

[DJ]

Re: What Is My Tach Saying To Me?

Your rectifier is NOT watercooled. However, it is most likely the culprit.<br /><br />Easy to check. Put a volt meter across the battery terminals and start the engine. If you get over 13 volts, it's charging.

 

[Joe Reeves]

Re: What Is My Tach Saying To Me?

On the 1985 90hp Evinrude/Johnson, the rectifier could be either model ie small 3 wire rectifier or the large water cooled one.<br /><br />Look on top of the engine just to the rear of the flywheel. If there's a raised component there with various wires leading out of it... a RED one leading to the starter solenoid, also a few others including a GRAY wire leading to a terminal strip (there will be another GRAY wire connected there that leads to the tachometer)... that would be a water cooled regulator/rectifier.<br /><br />Should you have the water cooled one, find the GRAY wire that leads to the engine's wiring harness which would be the wire that leads to the tachometer sensor. Move that tachometer GRAY lead from that terminal to one of the YELLOW terminals that leads to the stator. You might need to try both YELLOW wires.<br /><br />If the tachometer now operates as it should, then obviously the tach is okay..... but the regulator/rectifier is not!<br /><br />If this component is faulty, do not put off replacing it as eventually they become extremely hot and a fire results.<br /><br />Let us know what you find.

 

[Salty Tricks]

Re: What Is My Tach Saying To Me?

Thanks Again Guys<br /><br />I assumed it was water cooled because it has sealing compound on the bottom of it. My 1985 OMC parts catalog list two rectifiers distinguished by whether the motor has power trim and tilt. Hence why I mentioned the T and T in my motor description. But I wasn't certain it was water cooled. Joe's description confirms it. Will let you know how the test goes.

 

[Salty Tricks]

Re: What Is My Tach Saying To Me?

Did what you said Joe and tach works fine jumping grey harness wire to yellow wire at motor terminal strip. I guess that leads me to a bad rectifier. Could this also have hurt the stator or other component? Is this an easy "replace new part with old part" repair?<br /><br />Thanks for your time....really!!

 

[Joe Reeves]

Re: What Is My Tach Saying To Me?

Joe.... As per my email (copy below)<br /><br />Joe..... Well at least you know that $100+ tachometer is okay. I couldn't tell too much from the pictures you sent me unfortunately but those small battery charging coils should be a bright copper color with a varnish like protective coating.... in the pictures, they appear to have a hot fried appearance and that can occur from running the engine with a faulty regulator/rectifier as that causes the voltage to either back up into the stator or simply do very weird things.<br /> <br />The water cooler regulator/rectifier should have prevented the voltage from exceeding 14.5 volts. The reading you state of 15.7 volts is an unusually high reading, which in turn usually indicates the regulator/rectifier is faulty.<br /> <br />You'll need to make the determination about replacing the stator. However if you've owned the engine for a few years and have used it fairly often, and have not replaced the stator previously..... personally I'd replace it as that 35 amp stator does run extremely hot and eventually it will melt down.... and it will happen again at some time in the future. It's the nature of the 35amp stator due to the heat involved.<br /> <br />The regulator/rectifier..... no question there..... replace it. Sorry I couldn't be of more help with the stator.

 

[Salty Tricks]

Re: What Is My Tach Saying To Me?

Looking into getting a rectifier now....new one at local is $245...ouch. Trying to determine if stator is damaged. Thanks for all your help. regardless of the outcome you folks saved me a bundle...I reallly appreciate the time you guys give here. Particular thanks to Joe...I don't know how or why you do this but you are a boater's Godsend...Thanks

 

[Joe Reeves]

Re: What Is My Tach Saying To Me?

We don't know why we do it either, but we spend the rest of our time trying to figure out where to send these bills (grin).