Tach and charging system HELP please

[Alex Pullen]

I have a 1984 90hp johnson V4 on a 16ft fiberglass bass boat, and i have recently developed charging? problems and tach problems. i originally had a problem with fuel delivery(bad pump) and low rpms(3800 max @w.o.t.). fuel problem is fixed and the motor runs like new, however now my tach will only read to 42+/- and my battery doesnt seem to hold a charge. the charging problem just recently started and the tach was in the boat when i bought it and it worked and then it quit. i had the steering replaced and the tach worked again(screwy). i do have a new tach on the way but i guess my main ? is does the charging system affect the tach and would it cause it to read low or wrong? my tech says i am under propped and the tach should read about 6000 which is too high, so i also went to a higher pitch prop(more speed)but i havent tested it yet.He says the rectifier might be the cause, but i am trying to get a second or third opinion. Thanks for any help.

 

[Beernutz]

Re: Tach and charging system HELP please

Rectifier/regulator is the prime suspect. Don't waste money on a new tach til you check out the R/R.

 

[Alex Pullen]

Re: Tach and charging system HELP please

thanks for the help but i am no where near being a tech. Could you take the time to give me specific instuctions to check the rectifier and regulator? (i can get a voltmeter if i need one. <br /> Thanks, Alex

 

[Beernutz]

Re: Tach and charging system HELP please

Alex, '84 was a change-over year. I'm assuming that you have a power tilt & trim model with the integrated rectifier/regulator. If not, they may very likely be two separate modules. In any event, you'll need specialized test equipment and/or knowledge to perform the necessary tests. I presume that your tech checked your stator, before he arrived at his diagnosis. If so, I merely concur with him. Your failure mode fits the scenario.<br /><br />This one is best left to the tech.

 

[JRJ]

Re: Tach and charging system HELP please

An engine tech told me that my idea of letting the motor charge both batteries at once was why my tach and alternator weren't working right. A diode or something blew in the alternator. Since then I alternate batteries every trip and haven't had any more trouble. I don't know what the deal is, but I'm sure someone around here does.

 

[clanton]

Re: Tach and charging system HELP please

Need to know what system on this engine. My book show water cooled regulator, but could only have simple rectifier with no voltage regulation. Tach gets it signal from the stator, on V4 V6 with regulator the signal/pulse is fed thru the regulator, and on these systems, bad stator, regulator, or both will cause tach not to work. The systems with simple rectifier, tach pulse is pickuped before the rectifier, but shorted rectifier will cause tach not to work. On this system disconnect yellow/gray lead from rectifier, if tach works, rectifier is bad. You need peak reading meter to check tach output from regulator, should have 8/9 volts with tach connected.

 

[clanton]

Re: Tach and charging system HELP please

6000 rpms is too high for this engine.