Tohatsu M90A mid to high speed electrical miss

[outboardnut]

I have a 1998 90 HP 2 smoke Tohatsu model M90A.

The girl has a mid range to high speed miss. Approx 3K plus it's acting up.

It is electrical. I'm seeing erratic spark when she's acting up.

I'm seeing a voltage drop between the white/green and white/yellow leads when the miss shows up.

It puts out about 200V at idle speed between these two, and drops to 90V at mid range when the miss starts.

CDI states I should have 135V min between these two wires.

Also seeing low voltage coming to the coils once the miss starts happening, so the system seems to be starved for volts or it's shorting in the power pack.

I'm not exactly sure what they are, or where all my needs volts are going.

I isolated the wires and did a DVA to ground motor running, the white/green I'm seeing 200 volts until the miss starts up, the other I'm seeing about 12.65 volts, and it stays steady.

Any suggestions on troubleshooting this further?

 

[pvanv]

Re: Tohatsu M90A mid to high speed electrical miss

Run through the ohm checks in the service manual to (hopefully) determine which unit is at fault. Although they are done with the motor off, you may find something that's way out of spec.

 

[TOHATSU GURU]

Re: Tohatsu M90A mid to high speed electrical miss

Is it an erratic miss or a rhythmic miss?

 

[outboardnut]

Re: Tohatsu M90A mid to high speed electrical miss

It's erratic.

I"m betting on the exciter. I tried disconnect temp, water pressure, and oil pressure switches and it still acts up.

The exciter ohmed out fine. I tried to ohm out the switchbox but I don't trust my readings and text.

I'm not finding much documentation for this motor. I have the factory service manual which is very vague and also but the Seloc version.

 

[TOHATSU GURU]

Re: Tohatsu M90A mid to high speed electrical miss

Are you using a digital meter?

 

[outboardnut]

Re: Tohatsu M90A mid to high speed electrical miss

Yes, fluke 88 with a CDI peak DVA adapter.

I can see the voltage coming from the excitor dropping off at approx 3k RPMS. It then in turn is starving the rest of the system.

The trouble is I'm not exactly sure why the voltage is dropping. If there is something in the powerpack pulling it down or the excitor is just crapping out.

I tried disconnecting the oil level sensor, overheat sensor and water pressure sensor.

Any help is appreciated.

 

[outboardnut]

Re: Tohatsu M90A mid to high speed electrical miss

o yea I tried ohmign the two also.

The excitor ohmed out fine.


Ohming out the powerpack calls for a Tohatsu radio tester, tried using my fluke and another one. My readings were off but I don't trust them. I've seen pulse packs ohm out wrong and work just fine and this manual is calling for really sensitve readings.

 

[TOHATSU GURU]

Re: Tohatsu M90A mid to high speed electrical miss

Use an analog meter and run the checks again. It's probably the CD.