Tachometer failure or more WHO KNOWS??

[Hydraulica]

G'Day Gentlemen & Ladies who find an interest.

I have a question for the electrical & mechinally minded boaters.

I have just completed 9 hrs of engine running my 200 Mercury V6 (over a couple of days) after a 2nd rebuild. See hydraulica previous post for details.

The boat had a flat battery prior to todays running, so it was charged on a 6.5ma charger for 12hrs to full capacity. 650cca battery. Battery was drained in testing. My mechanic advised me to charge the battery, but i was a bit lazy over the festive season & i was caught out(girlfriend wasnt to happy...paddling).. trap for young players...beware..

Today i went for a 2 hr drive in the boat. In the lat 10 minutes of driving on the way to the boat ramp in the boat obviously, the tachometer starting to malfunction, not reading the right RPM going backwards on acceralation, reading 1500rpm when the engine was revving at 3500rpm. The guage eventually stop working.

I went home, fitted an alternate guage, to eliminate the obvious problem, but still no tachmeter reading. On ignition or initial start up the guage jumps to 1500rpm (momentarily) then (zero)0 rpm with the engine still running.

What The?

Regards

Hydraulica

Sydney Australia

[The Big Al]

OK, first I will assume you have a 2.5 200 with a 40amp charging system. 1992-2000 model

See the tach works of the charging system, not the ing. system.

And with a 40amp system you have 2 voltage regulators mounted behind the ing coils. Both regulators have a tach hookup. ( GREY WIRE) So what you can do as a test is disconnect it from the regulator it's plugged into and plug into the next one. If tach works correctly you have a bad regulator. You can also remove the coil bracket as in the illustration and look to see if reg are burned. Most have a clear back and can see burns.
Hope this helps.

NOTE: item "C" is the Grey wire

http://img411.imageshack.us/img411/9641/mercury40ampsystemvh0.png (http://forums.screamandfly.com/forums/)<SCRIPT type=text/javascript>setImgWidth();</SCRIPT>
http://img147.imageshack.us/img147/777/mercury25voltagereg2ft1.png (http://forums.screamandfly.com/forums/)<SCRIPT type=text/javascript>setImgWidth();</SCRIPT>

[Hydraulica]

Thanks Big Al..

I will be under the hood first light..


Regards

Hydraulica
Sydney Australia

[Tony Montana]

great answer big al, that's what I call advice!

[M.CHAPMAN]

You may also want to check all the grounds, especially the one on the coil plate, bad grounds can cause irratic tach readings.

[Hydraulica]

Thanks Michael.

[The Big Al]

What did you find?

AL

[Hydraulica]

Hello Big Al,

the rectifier has to be replaced,
I will be collecting one from my mechanic in the next 24hrs & fitting it.

Regards

Hydraulica

[Hydraulica]

I replaced the rectifier today (Saturday), tacho is working fine now.

After fitting the rectifier, I took the boat for a drive & can feel I have a severe continual miss & the motor is well underpowered. (this is a new problem). Could this be a coil. Checked all leads etc. How can i test coils. Do i remove 1 spark lead at a time looking for a spark on ignition.

Regards

Hydraulica

[rarias]

I had the exact problem you are presenting hydraulica.

How I solve it:

1. Changed the rectifier and stator.
2. Check for bad grounds.
3. Mechanical Tachs can be adjusted for V4/V6/V8, check for right position.
4. Spark Plugs in good condition ??
5. Check Coil, start engine and with the proper tool. one by one take plug boot off while engine running you will notice that the engine will drop RPM and will try to stop imidiately put it back and do this to all 6 of them. If you take boot of spark plug and nothing happens you have a problem with coil or either the power pack.

Good Luck,

Raul

[j_martin]

Sometimes the heat of a shorted rectumfier can cause trouble in the charge coil parts of the stator. They use different coils, but are on the same piece of iron. A DVA check at the switchboxs should check that out.

hope it helps
John