75 Merc No Fire

[ablebakercharlie]

New guy, here. Bear with me, please.
I have a 1994 - 75 HP Electric Start Merc that is getting no fire. Will a bad rectifier/regulator cause this. Checking with VOM indicates possible problem. Continuity check of stator is OK. Any good ideas or suggestions?

 

[LoneWolf_2010]

Re: 75 Merc No Fire

Hello , i had a similar problem and with help fromo the guys on here i fixed it, mine was the stator you can look for my old posts and the should help you. I would also invest in a DVA meter or adapter for you multimeter this is the only way read voltage on these outboards i bought mine from USA toolwarehouse for 30.00 bucks but i boats has one to i believe also you can check out this website www.maxrules.com and look for the troubleshooting section and it will help. Let me know if this helps thanks.

 

[ablebakercharlie]

Re: 75 Merc No Fire

Thanks for the response, Lonewolf.
I have a DVA tester, the stator shows no reading on the low speed windings but does read on the high speed.
What puzzled me was the continuity of the stator indicated it was OK, but the LS windings indicated something else.
Just thought maybe the rectifer/regulator could be the root of the problem. When I sort everything out, I will post the solution.

 

[LoneWolf_2010]

Re: 75 Merc No Fire

hello again try to unhook the stator wires from the switchbox and use the ohmmeter again i am assuming you probably already did this but sounds to me like it is the stator atleast thats what my problem was i had voltage on the highside and not the low but when i used the ohm on the low it read OL wich is open loop i replaced the stator and VROOOOOOOOOM check out the web site i said and good luck.

 

[achris]

Re: 75 Merc No Fire

...Just thought maybe the rectifer/regulator could be the root of the problem. ....

Not a chance... The rectifier/regulator has absolutely no influence on the ignition system whatsoever. The only thing common between them is that they both reside under the engine cover.

If you have a shorted turn in the stator then the resistance readings will look ok.... That's why the only valid test method with outboards is a DVA... It can't lie to you...

Chris.......

 

[ablebakercharlie]

Re: 75 Merc No Fire

Thanks for the advice. I was confused by what I was seeing. I will replace the stator and see where that takes me.

 

[ablebakercharlie]

Re: 75 Merc No Fire

After replacing the stator, everything works fine.
It took a while to assemble the special tools and get parts.
I went back to square one and retested everything and did not read anything into the results.
Thanks to those who responced to my original post, you made me stop and think about what I was doing.

 

[CDI Tech Support]

Re: 75 Merc No Fire

New guy, here. Bear with me, please.
I have a 1994 - 75 HP Electric Start Merc that is getting no fire. Will a bad rectifier/regulator cause this. Checking with VOM indicates possible problem. Continuity check of stator is OK. Any good ideas or suggestions?

CDI Troubleshooting Guide

Shortcut:

Mercury 3 Cylinder

Resistance is a highly unreliable measurement. DVA is a highly accurate measurement.

One must have a DVA Adapter plugged into a digital meter to accurately read DVA (peak AC voltage) on an outboard. No digital meter on the market has built-in DVA.

DVA Explained

If purchasing DVA equipment is impractical, we suggest printing off the troubleshooting pages & taking them & your engine to a qualified marine mechanic.

 

[CDI Tech Support]

Re: 75 Merc No Fire

Not a chance... The rectifier/regulator has absolutely no influence on the ignition system whatsoever.

Negative. If the regulator/rectifier has a diode that is shorted, it creates a 2-way path where DC from the battery can enter the stator's electromagnetic AC field.

A faulty regulator/rectifier can cause anything from a No Spark condition to a high-speed miss.

Simply disconnecting the stator's two Yellow wires from the regulator/rectifier isolates the regulator/rectifier out of the circuit. This has been verified numerous times.

 

[achris]

Re: 75 Merc No Fire

...
If purchasing DVA equipment is impractical, ....

You could just build your own for under $10... http://forums.iboats.com/showthread.php?t=374544

Chris...........

 

[achris]

Re: 75 Merc No Fire

Negative. If the regulator/rectifier has a diode that is shorted, it creates a 2-way path where DC from the battery can enter the stator's electromagnetic AC field.....

No it doesn't. The current flow is blocked by the other diodes. If 2 diodes are shorted, they don't stay that way for very long (measured in milliseconds, about long enough for the current to blow one open). All that will happen is that a shorted positive diode will reduce the output current, and introduce some ripple, but only on the charging system. 12 volts from the battery isn't enough to influence the 400 volts from the ignition stator.

As I stated earlier, the charging system and the ignition system share the engine block, nothing more.

As later stated by the OP, he replaced the stator (not the rectifier/regulator) and the problem was solved.

Chris.......

 

[CDI Tech Support]

Re: 75 Merc No Fire

No it doesn't. The current flow is blocked by the other diodes. If 2 diodes are shorted, they don't stay that way for very long (measured in milliseconds, about long enough for the current to blow one open).

A shorted diode can stay shorted indefinitely. How else would we be able to verify a diode can short? If they all shorted to point of opening, we'd never be able to verify a shorted diode.

All that will happen is that a shorted positive diode will reduce the output current, and introduce some ripple, but only on the charging system. 12 volts from the battery isn't enough to influence the 400 volts from the ignition stator.

Absolutely 12VDC can influence 400VAC from a stator, especially at the amperage associated with a battery.

As I stated earlier, the charging system and the ignition system share the engine block, nothing more.

On most outboards, a stator & a regulator/rectifier share the same ground frame & laminations, thus they share the same electromagnetic field. The charge coils on a stator also share this same ground frame & laminations, thus they share the same electromagnetic field.

When a stator & regulator/rectifier do not share the same ground frame, as in the case of a Mercury 2 cylinder 339-7452 ignition, isolating the regulator/rectifier from the circuit is futile, making your statements correct.

More often than not, when a stator's battery charge windings show "browning" by shorting together, a shorted regulator/rectifier has caused this. Occasionally, excessive heat will cause the stator's protective varnish to melt, causing a stator's battery charge windings to "brown" by shorting together, but those cases are in the minority. Excessive heat typically causes a widespread stator "browning" or shorting. A shorted regulator/rectifier typically causes "browning" or shorting on one stator pole.

As later stated by the OP, he replaced the stator (not the rectifier/regulator) and the problem was solved.

A charge coil on his stator failed, not the regulator/rectifier, which is, in numbers, by far a bigger No Spark culprit than a failed regulator/rectifier.

Again, we have verified through numerous troubleshooting calls over the years that disconnecting the regulator/rectifier has solved No Spark conditions & high-speed misses.

That's why we list this troubleshooting step in all applications where a stator & regulator/rectifier share the same ground frame. It's simple to do & doesn't require meters or other equipment. We've seen plenty of instances where guys wasted time and/or money by omitting this step. It doesn't happen as often as other issues, but we've seen it enough to warrant mentioning in nearly every application in our troubleshooting guide.

We would certainly welcome you to contact us by phone to verify these statements. Ask for Sean. He'll be more than happy to discuss.