no tach, rectifier replaced, nothing

[surrender]

Rectifier was bad so i replaced, battery charging good now. Tach was not working, was hoping rectifier replacement would cure, no luck. Have 12 volts at ign terminal on tach at key on position. On tach terminal (gray wire from engine) have zero volts at off, 6 volts and change when running, no increase(or decrease) when throttle changes position. My guess is bad tach. It is probably original to boat (1987) or motor ( 1996 johnson Special 88) Anyone have any input. Oh yeah, engine has a higher idle(by my ear, no tach) since i changed rectifier.

 

[ezeke]

Re: no tach, rectifier replaced, nothing

Did you check the other wires on the tachometer? Use your ohmmeter to make sure that the ground is good.

If wiring seems OK, try switching the gray wire at the engine to the other yellow wire on the terminal block.

 

[surrender]

Re: no tach, rectifier replaced, nothing

The other wires read as follows:
Ground to ign; key off-zero volts, key in run(engine running) 12.67 volts
Ground to tach wire; key off- zero, key in run(engine running) 6.37 volts
No change when revs increase.

What other wires are there?

 

[ezeke]

Re: no tach, rectifier replaced, nothing

Three wires: purple 12 volts from acessory post on ignition switch; Gray signal from engine; Black, ground to engine from small M post on ignition switch - use ohmmeter to check ground wire for continuity to the engine block.

If wiring seems OK, try switching the gray wire at the engine to the other yellow wire on the terminal block.

 

[wilde1j]

Re: no tach, rectifier replaced, nothing

Gray lead can't be checked with a voltmeter. It's pulses, not a continuous voltage. Quickest test is try a known good tach ... if it works, yours is bad. Purple 12 VDC is irrelevant to the tach, except for internal illumination. The tach only needs a ground (black) and grey (pulse feed).

 

[ezeke]

Re: no tach, rectifier replaced, nothing

As I said: use ohmmeter to check ground wire for continuity to the engine block.

 

[surrender]

Re: no tach, rectifier replaced, nothing

Gray lead can't be checked with a voltmeter. It's pulses, not a continuous voltage. Quickest test is try a known good tach ... if it works, yours is bad. Purple 12 VDC is irrelevant to the tach, except for internal illumination. The tach only needs a ground (black) and grey (pulse feed).

i just realized that thew gray wire is a pulse but could you set a multi meter to AC voltage on the smallest range and see if it pulses, see if you get a pulsing reading? Anyway I will try switching gray tach wire to other yellow on terminal block.

i get a voltage reading of 12 and change on ignition wire on tach when tested across that wire and the ground terminal on tach. Wouldn't that mean ground is good. If not would i get the reading?

 

[ezeke]

Re: no tach, rectifier replaced, nothing

You should not have voltage on the black ground wire. How is it connected - through the three wire amphenol plug on the remote control?

 

[surrender]

Re: no tach, rectifier replaced, nothing

i dont have voltage on the ground. I have voltage at the ign wire on the back of the tach when tested across ign-ground wires. Thats with the key turned to the on position. thats good, the tach would light up if the bulb worked. its old fashion wires, no three wire plugs just a pole for ign, tach and ground.

 

[King P.V.]

Re: no tach, rectifier replaced, nothing

The grey wire will need to be check'd with a peak-reading voltmeter, not your usual voltmeter you have laying around the house. It shoiuld be 11 volts plus/minus 1. The way to read if your rectifier is working is to also use a regular volt meter across the battery. Preferably a digital one. Read the battery voltage without the negine running, then after it starts and watch the voltage go up. An analog meter really won't show much change but a digital one will show you the minute' changes of voltage. You could also exchange the tach for a known good one.

 

[ezeke]

Re: no tach, rectifier replaced, nothing

How is the black ground wire connected to the motor?

BTW see item 3 here: http://www.downloadingfiles.co.uk/teleflexfiles/gauges/Tachometers Outboards.pdf

 

[surrender]

Re: no tach, rectifier replaced, nothing

Thanks King. i know the rectifier is good now(put a new one on Sat,battery was NOT charging and it tested bad) and the battery is now charging, my digital volt meter confirmed that. The tach is bad. everything else checks out.

 

[ezeke]

Re: no tach, rectifier replaced, nothing

The grey wire will need to be check'd with a peak-reading voltmeter, not your usual voltmeter you have laying around the house. It shoiuld be 11 volts plus/minus 1. The way to read if your rectifier is working is to also use a regular volt meter across the battery. Preferably a digital one. Read the battery voltage without the negine running, then after it starts and watch the voltage go up. An analog meter really won't show much change but a digital one will show you the minute' changes of voltage. You could also exchange the tach for a known good one.

Gray wire signal voltage is read from the gray wire to engine ground with the engine running. It is an AC voltage and can be read with a AC voltmeter. The voltage will read above 3.5 AC at idle and from 5 to 7 AC at +/- 2,000 RPM.

 

[surrender]

Re: no tach, rectifier replaced, nothing

Gray wire signal voltage is read from the gray wire to engine ground with the engine running. It is an AC voltage and can be read with a AC voltmeter. The voltage will read above 3.5 AC at idle and from 5 to 7 AC at +/- 2,000 RPM.

Yeah thats what i have. Engine is at high idle and that reading is 6 volts. Tach is bad. All connections from engine are rerading as they should and tach doesnt zero out as it says in number 4 of your previous post.

 

[surrender]

Re: no tach, rectifier replaced, nothing

Ok back to this one. Waiting on a new tach and in the mean time was checking again and found something wrong. I am reading 14.7 volts AC at the grey wire going to the tach. Before I put new tach on I need to correct this. I replaced the rectifier with what I thought was a good one but maybe not. It came from a boat recycler shop and it looked brand new. I know it was not new but they said it "should" be good. Ok so now how do I check the output to the rectifier to make sure the problem is not further up the line: ie: stator.

 

[wilde1j]

Re: no tach, rectifier replaced, nothing

to check stator, you should get > 25 VAC across the yellows (engine running of course and everything connected). If not, stator is suspect ... check the wiring first and if OK, stator is likely bad. However, an even simpler check for the rectifier and stator is to read DC voltage at fast idle across the battery terminals. You should get 13+ VDC if everything is working. Note, as a reference, a fully charged battery will read a static voltage of ~ 12.7 VDC and the normal running charging voltage will typically be 13.5 to 14 VDC.

 

[surrender]

Re: no tach, rectifier replaced, nothing

Just rechecked the rectifier using Joes method; check resistance bothways, ect. It checks out. Voltage at battery is 12.5 engine off. 12.8 engine running at idle, not fast idle. Will recheck.

 

[surrender]

Re: no tach, rectifier replaced, nothing

Checked again. I get 1.6 ohms across yellow-yellow/gray from stator. No continuity between yellow and ground. and same between yellow/grey and ground. No continuity is good, 1.6 ohms may be a little high right? Also, while running I get 15.7 volts between stator wires and it increases as rpms go up. Not high enough? Note I am checking stator output at yellow -yellow /grey with a regulat voltmeter.. Do you need a DVA peak meter to read the 25 volts I should be getting? My guess is I need to go get an adapter for my meter. I have a craftsmen meter...off to sears to see about an adapter. Thanks

Oh yeah. My uncle loaned me an old tach/dwell meter. I hooked it up the the grey tach wire and a good ground and it read 1600 rpms on the 8 cylinder scale at idle(its for 6 and 8 cylinders, says to "double "readings for 4 cylinder). Rpms increased on this meter when I advanced the throttle. I think for rpms you half the readings with this meter. That would be 800 rpms at idle on a hose. Would make sense.

 

[wilde1j]

Re: no tach, rectifier replaced, nothing

I have no clue about the resistance between the yellows ... maybe an OEM shop manual would tell. If the AC voltage goes up w/ RPM, the rectifier may be fine, although I would expect a little more. I would wait for the new tach to show up before doing anything radical. BTW, you don't need a DVA for reading the AC across the yellows.

 

[surrender]

Re: no tach, rectifier replaced, nothing

Thank you all. I think all is good. Will check when new tach gets here.