Bad Rectifier/Regulator??

[Psalm 99]

Engine is a Yamaha 150 TXRC. Getting a new engine but still trying to find problem with this engine which only has 609 hrs on it. Problem is electrical/electronic. About the only thing not replaced or tested is the voltage rectrifier/regulator. Never thought to check it. However, the tach goes haywire when the engine reverts to 'limp' mode. Lot of false hopes with trying to fix the problem but per the Mechanics Manual for this engine, the data across leads using an ohm meter sure looks bad: There is no continuity when correctly placing the leads on any of the three positions (black lead common). For these three positions, manual indicates continuity where meter reads 4, 4.3, & 8.2 mega ohms. Reversing the leads, manual shows open circuit (infinite resistance) where meter shows 11, 17, & 5.2 mega ohms. Rectifier/regulator sure seems to be a problem. Would it's failure cause the engine to go into 'limp' or 'rpm reduction? This problem has been getting progressively worse until it occurs with the engine on muffs and at start-up. Seems reasonable as the rectifier is cold and removed when I tested it and it seems shot. Thanks for the help!

[zenoahphobic]

Be careful using the multimeter, when getting high megohm readings sometimes moisture or touching the probes with your hands can give these readings. The alert here I see, is infinity is called for and reversing produces less - the reverse of what is expected.
Check again, those readings probably indicate the R/R is open circuit. What output voltage is there when engine is running should give you a clue about whether it is faulty.

[rodbolt17]

thids is to easy.
what Volt reading is at the battery before starting?
what is it at 1200 RPM?
if it raises a volt or so between not running and running go find another bunny.

[boscoe99]

As rodnut suggests, check the battery voltage prior to first start of the day. Should be more or less 12.7 volts if fully charged. Start the motor. Run the motor at a fast idle. Voltage measured at the battery should be more or less 14.5 volts. If so, the R/R is doing its job.

If the voltage does not rise, then check the output from the lighting coil to the R/R. If the output from the lighting coil is below specs, replace the lighting coil. If the output from the light coil meets/exceeds specs, replace the R/R.

The CDI putting the motor into RPM reduction mode should have no effect on the tachometer reading. Other than tachometer reading lower than it might otherwise read, since the CDI prevents the motor running above X RPM.

Low voltage can put the motor into RPM reduction mode. Low voltage can result from many things. Poor grounds, poor wiring, poor connections, etc. These are the most likely reasons for low voltage.

[Psalm 99]

Voltage output is fine. 12.7 V raised to 14.4 with engine at high idle (1500 rpm). However, testing leads from the lighting coil per manual with a peak DC voltage adapter installed, The coil output reads about 55 VDC peak. Manual says a reading above 35 VDC peak @ 1500 rpm requires a replacement of the R/R. Maybe I'm doing this wrong as I test the coil with the plug to the R/R unhooked. It would need a special harness to test the leads with the plugs connected.

I tested the R/R using an old dial type ohm meter. Got data which was more understandable. Where the manual says there should be infinite resistance, the unit tests correctly. Where it says there should be an open circuit, all three points register about 15 ohms. Seems sensible as there will be some resistance and the unit charges correctly.

[boscoe99]

Where in your service manual does it say to replace the R/R if the lighting coil output is above 35 VDC @ 1500 RPM?

Why would the R/R need to be replaced if another component (the lighting coil) output is incorrect?

What I see is that the lighting coil should be at a minimum of 35 volts.

[Psalm 99]

Page 8-32:

MEASURING THE LIGHTING COIL
OUTPUT PEAK VOLTAGE 8
Measure:
• Lighting coil output peak voltage
Above specification → Replace the
rectifier/regulator.
Below specification → Replace the
lighting coil.

I'm confused also. Measuring the lighting coil output is upstream of the R/R.

[boscoe99]

The R/R is tested first if and when a problem is suspected. Say the R/R is below output. It could be the R/R or it could be the input to the R/R. The lighting coil is the input.

If the lighting coil is above specification but the R/R is below specification then change the R/R. Input is good but output is bad.

If the lighting coil is below specification then probably that is the reason for the low R/R output. Low output in = low output out.

In your case the lighting coil is above specification and the R/R is above specification. All is well. Input is good and output is good.

[rodbolt17]

and remember, the RR has NOTHING to do with the tach. tach send is a function of the pulser coils and ECU.
go hunt another bunny.

[boscoe99]

and remember, the RR has NOTHING to do with the tach. tach send is a function of the pulser coils and ECU.
go hunt another bunny.

To set the record straight, and for those that come along and read this thread later, rodnut is talking about the OP's specific motor only. Not all Yams are alike. In some, the tachometer signal comes directly from the lighting coil. Other Yams may, repeat may, be different. The way that one Yam model works won't necessarily work the same way in a different Yam model.

[Psalm 99]

I'm not sure where my tach signal comes from, just that when the engine goes into 'limp' mode, the tach is wildly inaccurate for a short time. New engine arrives next month but even with only 609 hrs on it, my 2-stroke is only good for parts unless I can solve this problem. Rodbolt is right about looking for a different bunny. No alarms sound when the engine kicks into 'limp' mode and I'd heard this can happen when the charging system is at fault. Hence the look into the lighting coil & R/R. I've cleaned all the connections and grounds a number of times. About the only major pieces of equipment not replaced are the stator and wiring harnesses. I'm in Boscoe' camp about the problem being a bad connection somewhere, but after two years of trying to deal with this problem, I'm sure looking forward to the new F150. Still, its hard to give up.

[boscoe99]

Look at all of the fuses. Are they tight? Maybe replace them for the hellavit. Inspect all of the electrical connections anywhere on the motor. Anywhere in the boat. Disconnect and reconnect the connectors to help improve conductivity. Look for loose wires. Restrain them with tie straps. Don't forget the connectors to the CDI.

[zenoahphobic]

Remember diagnosing is a steady methodical approach. Things carefully checked and cleaned then ticked off list.
Going at it like a bull in a china shop, throwing parts at it, is a hit and miss affair with a risk of creating a further fault.

I know of one case where this new 4wd wasn't running properly, thousands of dollars worth of parts where replaced. Changing things did often appear to be working but the erratic running kept returning.
The ultimate part was eventually replaced, and that was the ENTIRE CAR! under "lemon" laws.
But the fault eventually returned! Yes even in the new car!
Proper diagnoses eventually lead to bad fuel! They think the local garage had a habit of adding surplus stuff to his fuel including the mixing of different octane ratings when a pump ran out so he wouldn't loose sales.

[rodbolt17]

low voltage sets an audible.
anything that sets RPM reduction, lets not say limp, also sets an audible.
go hunt other bunnies.
RPM reduction on that motor limits RPM to about 2500 and the motor will shake like a concrete mixer.
below 2500 you may not notice it.
that is why I like to rig boats properly.
properly rigged and you can simply observe and eliminate.