Evinrude 120 Tach Problems

[Lucrestyle]

know this has been covered a million times on here, and i did the search but sometimes problems can be unique.

boat- 1989 Larson Senza 165
engine- 1993 Rude 120hp

Problem- tach never worked properly before on previous engine 90hp... current condition - itermitten tach now (works but fails at WOT)

I checked all wires according to teleflex, it was set to 6.
the tach will work up to about 3 / 3500 grand - then at WOT it will fail.
if i slow it down the tach picks back up.
the tach does zero out when i turn the key to on position.

any idea's, what should i check first... does this sound like a ground problem to you, i have three black ground wires leading off the tach.

should i sand down / scuff terminals to get better conductivity?
should i follow ground wires to check actual grounds?
does this sounds more like a rectifier problem?

any help would be awesome! thanks fellow boaters!
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[hoeser]

Re: Evinrude 120 Tach Problems

I'd put my money on the rectifier. Had the same issue on my 84' 140 and it behaved exactly as you described. Check your charging voltage at the battery, should see 13+ at a fast idle.

 

[Lucrestyle]

Re: Evinrude 120 Tach Problems

thanks for the reply, does anyone else have any suggestions?

so the first thing i will do is check for 12v at battery with the engine off? then voltage with engine running and then voltage with a high mid idle? if i have good voltage coming into the battery while the engine is running that means my rectifier is good correct?

 

[hoeser]

Re: Evinrude 120 Tach Problems

Well, "good" is a relative term. I would check it at WOT on the lake as well, I don't suppose you have a gauge? I've heard of this problem cropping up with an overcharging regulator (ie: 14.5V or more). When it happened to me, it was just dead entirely.. the voltage stayed identical at all engine speeds.

 

[Lucrestyle]

Re: Evinrude 120 Tach Problems

yeah i have a gauge. i am going to try it out tonight in the yard, check the voltages at idle and med/high idle to see if there is anything funky going on.

i will provide this history, the rpm gauge was not working the other day so i tightend up the ground wires and now it works to 3500 rpm could there be a problem with conductivity on the grounds still and that would be causing the problem?

 

[PondTunes]

Re: Evinrude 120 Tach Problems

You do have 2 threads on the same basic question... Did you read the reply in the electrical thread?
http://forums.iboats.com/showthread.php?t=200630