Tach or Rectifier?

[consultpsc]

Hello,
I am new to this site.
I have a 1990 Evinrude XP 150 on my 1992 Ranger boat.
Recently, the tach began to malfunction showing loss of RPM then jumping back up to normal readings. The tach finally quit working completely.
I have been researching how to troubleshoot the tach verses Regulator/Rectifier (RR) and I'm not sure I understand how to do this.
Someone called Seahorse on this blog had tried to explain how to do this but I'm not sure I have performed the test correctly.
I turned the key "on" and took a voltage reading at the grey wire terminal screw, my fluke meter showed somewhere around 9 vdc.
I then disconnected the PUL grey wire from the back of the tach and took the reading again, it was now showing about 11 vdc at the grey wire terminal screw. I then disconnected the wires from the grey wire terminal screw and measured voltage just a the grey wire from the RR and it still showed about 11 vdc. I measure the other two grey wires which were connected at the terminal and they showed a very low voltage perhaps .6 vdc.
Is this telling me that the RR is bad?

Is there any other tests that I can perform to further evaluate this problem?
I can not run the engine right now because the boat is in my garage now.

Any help would be appreciated.
Consultpsc

 

[emdsapmgr]

Re: Tach or Rectifier?

You need a special "peak-reading" voltmeter to check the output to the tach. Set the voltmeter to POS and 50. Attach the red lead to the terminal strip gray terminal (tach signal wire) and the black lead to ground. At 1000 rpm, the voltmeter should indicate 9 plus or minus one volts. Tachs usually don't fail that often. Your current testing would seem to indicate the signal is ok-if your fluke meter is considered a "peak-reading" model. Did you check to see if the other two wires going to the tach are connected properly-ie, you could have ground issue...?

 

[Faztbullet]

Re: Tach or Rectifier?

If its been working fine and just started this, my bet its the rectifier. The new rectifiers (OEM & aftermarket) do not use the purple wire any more as its a update. Also replace wing nuts with locknuts on the battery as a bad connection will kill a rectifier as will a weak water pump due to engine block not filling completely at idle.

 

[consultpsc]

Re: Tach or Rectifier?

Thanks emdsapmgr and faztbullet!
I'll spend a little more time confirming wiring.
I've had this boat since it was new in 1992 and this engine was on it new, a left over from 1990, I guess because of the new ficht model that was fresh on the market.
Anyway, this engine has been great, no regrets at all. I do change the water pump every 3-4 years and this one is only 2 years old. Good flow at the telltail as well and no hot spots on the block. The engine is actually babied with respect to getting maintenance and routine service.
The engine only has about 200 hours on it, yeah not used very much.
For the last several years it has spent it's time on a lift in my covered dock on Lake of the Ozarks in MO.

I see that I'll have to pull the flywheel and stator to change the R/R if it is the problem.
My readings were using a standard mode voltmeter not peak holding and the reading were performed with just the ignition "on" but not enginer running.
I will go back and reconfirm my readings this weekend.
I will also do some tests that I found posted to confirm diode functions in the wiring of the R/R.

I would just change the R/R but I have not experienced a charging issue with my cranking battery and I don't want to find out that I now have to replace the tach. Right now, the Tach is the only issue.

I understand the new purple wire situation, I was looking at Mallory replacement R/R and they don't even have the purple wire on their replacement unit anymore.

I'll do somemore testing and post my confirmed results next week.

Thanks for your input.

Consultpsc

 

[wilde1j]

Re: Tach or Rectifier?

One very simple test is to measure the voltage across the battery terminals with the motor at fast idle (1200 to 1500 RPM). If < 13 VDC, either RR, stator, or wiring are bad.

An additional test for the stator is to measure the AC voltage across the yellows to the RR. If < 30VAC, the stator is bad.

 

[consultpsc]

Re: Tach or Rectifier?

Thanks Jim.
I think I'll give that a try too, I was told by my local Evinrude guy to do the same thing so I guess I'll get out the water muff and fire it up.
Consultpsc