1992 75HP Mariner problem

[sylvaing]

Hi, I have a 75HP, 1992, 3 pistons/2 strokes Mariner engine that
started to give me trouble last week. While a was pulling a tube, the
engine suddenly lost power and even at WOT, would not go over 2,600
RPM (while pulling the tube).

I tried the boat alone and even at WOT, the RPM would slowly increase
up to 3,400 and then jolted to 4,000 and then I had to pull the
throttle so it wouldn't go over 5,000 RPM (ie, from 4,000 and 5,000,
the engine was behaving normally). Below 3,400 RPM, the engine noise
is 'deep' and rough.

Thinking it could be an ignition problem, I tried starting the engine with just one plug connected at a time. The engine started with either the top or center plug but not with the lower plug. I swapped the lower plug with the top one and it still wouldn't start with the lower plug only so I know if wasn't a foul plug. I swapped the center and lower coil (and wires as well so the timing was still ok ) and same thing, the center plug was working with the lower coil but not the lower plug with the center coil so again, I confirmed the coils are ok. So it's either the switchbox, the stator or the trigger.

Is my diagnosis ok? How can I tell if the problem is in the switchbox, the stator or the trigger?

Thanks.

 

[Laddies]

Re: 1992 75HP Mariner problem

Heres the CDI test info

 

[sylvaing]

Re: 1992 75HP Mariner problem

Thanks for the reply.

My problem doesn't seem to be displayed on the sheet. In my case, the plug misfire (or not fire at all) until (not when) the engine reaches 3,200 RPM.

Also, is a DVA a Digital Volt Amp Meter?

 

[emckelvy]

Re: 1992 75HP Mariner problem

This is a "Direct Voltage Adapter" which would connect to a standard VOM for reading of peak voltages as discussed in the troubleshooting chart.

http://www.esitest.com/cart/640.html

You can't just measure output using a regular VOM without having one of these adapters.

Here's an excellent thread at this site regarding DVA's:

http://forums.iboats.com/showthread.php?p=1609186

BTW, fortunately most troubleshooting can be done "indirectly" by taking resistance readings and swapping components.

However, the DVA would help you get to a positive diagnosis if you have a particularly "pesky" ignition problem.

I'd look real close at the stator's resistance values as I've seen tons of motors having stator issues lately. Of course the stator is just one part to confirm or eliminate as a problem.

HTH & let us know what you find......ed

 

[sylvaing]

Re: 1992 75HP Mariner problem

Hmm, sounds to me that this DVA is nothing more than a diode (so the voltage doesn't feed back into the circuit), a high voltage capacitor (to keep the highest voltage) and a resistance (so it wouldn't drain the circuit power for a fraction of a second while the capacitor charges)... Am I right?

 

[Laddies]

Re: 1992 75HP Mariner problem

You seem to have all the answers, just start changing parts.

 

[CharlieB]

Re: 1992 75HP Mariner problem

If a cyl is NOT firing until 3200 wouldn't you call that

"No spark or Intermittant Spark" ?

Build your adaptor, and test your trigger, also look carefully at the trigger wires, one may be broken and not making contact inside its insulation until the timer is moved part way through its range. Test your trigger at different throttle positions to see.

 

[sylvaing]

Re: 1992 75HP Mariner problem

I haven't built the DVA yet since the engine started to work fine until today were it happened again So it's sporadic.

I checked the trigger wires for damage and got its resistance. All three wires shows a resistance around 1200 Ohm (which is within the 800-1400 Ohm the chart shows) and the resistance didn't fluctuate a bit when I bent/pulled the wires so my trigger looks fine.

Since the stator produces the sparks for all three plugs, am I to assume it can't be it since the problem happens with just one cylinder only?

If so, looks like the problem is within the switchbox, right?

Thanks again for your help.

 

[sylvaing]

Re: 1992 75HP Mariner problem

I subscribed to the Seloc Online Engine Repair Manual for my model and noticed that the stator has two charge coil. A 'low speed' one and a 'high speed' one.

I haven't checked its resistance yet but could it be the 'low coil' is producing barely enough voltage for two coils while the other coil is a bit more fussy and refuses to fire until the 'high speed' charge coil kicks in?

Thanks.