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Relationship between elec start and tachometer?

R

RCTerry

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My 9.9 four stroke Evinrude, elec start, tach in console, suddenly quit starting. Not even a click. Hand cranked, the tachometer read much too low and eventually dropped below 0 with the engine still running. A couple days later, I loaned the skiff to a friend and forgot to tell him to hand crank. Moot point, it started normally, tach normal, and has been running fine for 6 days now. any suggestions on how to head off future trouble?
 
Very good chance it is a battery terminals or cables problem. Connections must be clean and tight. Don't just look or assume, take the connections apart and clean them shiny bright. They will fool you as they develop a non-conductive layer of corrosion between the parts.
 
the relationship is this....you have a stator winding(separate from the run winding) that feeds a rectifier....the output of the rectifier does two things...a red wire off the rectifier terminal strip charges your battery..a grey wire feeds the tach...the output of the rectifier is not fully filtered and has pulses..these pulses are what the tach is measuring... you have an odd failure if the tach read low and then failed completely along with a dead battery if indeed the wiring is as i stated...rectifiers dont usually fail like that and then recover.. i think you have one of the following...a loose connection on the terminal strip...a bad stator as they will fail like that...the tach is wired from the positive post on the battery and you have a bad connection on the positive post...
i would do the following...go over the wiring for loose or corroded connection including the battery...measure the output of the rectifier(at 2k rpm) and record it..measure the input to the rectifier(ac) and record it...when and if it fails again you will have a reference point to troubleshoot from.....
 
The tachometer reads the pulses coming from the stator in reference to ground.

The starter gets its voltage from the battery + cable and returns it to ground.

Anybody notice a pattern here? The ground cable is the common denominator in both circuits.

Back to square one...my earlier post. Check those battery cables and connections. Especially the negative (ground) one. You have an intermittent connection there somewhere.

EDIT: Consider the timeline here. The problem appeared. Then the boat was loaned to a friend a few days later and the problem had disappeared. OK, during that time, was the battery disconnected for any reason? That may have disturbed or corrected the bad connection problem. Perhaps there is no problem now. It may not be broken and may not need fixing
 
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RCTerry said:
That's the first thing I did. What are the chances of a faulty ignition switch in the OMC control?
Click to expand...

Matter of fact, that is a slight possibility. But more likely a faulty 12V positive feed to the switch. The switch sends that 12V to the starter solenoid, AND to power the tachometer on. If the feed is intermittent, both would be affected. Check for a loose fuse, or a faulty or loose plug-in connection. Could even be a loose screw terminal on the ignition switch, although not too likely.
 
This is excellent advice, and gives me far better undstanding of what is going on and how to track it down. So far, the problem has not recurred, so it is not possible to report results - yet. But in my experience this is just the first sign of an existing problem. A little more info: the battery was brand new and all the connections were thoroughly cleaned, sprayed with contact cleaner, cleaned again and sprayed with Inox, a waterproof lubricant and protector after the connection was made to the terminals. I'm confident the problem is not at the battery. Because I could jump the solenoid and start the motor, but could not get the slightest click by turning the key, I'm suspecting the positive feed to the switch. the boat sits a lot, often six months between uses, but is going to be used quite a bit overr the next 3 months as I loan it to friends and clients who visit this time of year to see and swim with manatees (i'm in Homosassa Florida.) There's a chance the problem will not show up until next season, though it is troubling that it was running fine one day, then not, then fine again two days later. The only thing that happened between not working and working is that it got towed one block over a semi rough road to a boat ramp. That trip could have jolted the bad connection. thanks to everyone. i'm pretty sure now that I can find the problem next time around and will post the results here.
terry
 
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