Mercruiser 3.0 diagnosis / serial number decode

[Tube1]

The wire is merely a conductor to the points. The points are an electo-mechanical switch. When the points close (path to ground), the coil charges by creating a magnetic field. As the points open, the magnetic field collapses and that is what provides the high voltage from the coil secondary

What is so hard to understand?

There is a sticky on understanding points ignition. I would recommend reading it

I’ve read those threads exhaustively and have a good understanding of how the points system works.

Let me rephrase my issue.

The black points wire is connected to the “spring” side of the points, I’ll call this side 1.

However the minus (-) terminal of my coil is a direct short to my distributor body, AKA side “2” of the points setup.

Therefore when I connect the black points wire to the coil, it’s literally grounding everything together whether the points are physically open or not.

That’s what I can’t wrap my head around

 

[Tube1]

with everything connected (points wire attached to - side of coil), and with the points physicallyView attachment trim.250434CE-66A4-40A6-A2E3-10B6B7BBAE86.MOV open, I’m getting 5 ohms of resistance. Not an open.

 

[Tube1]

I disconnected the purple resistor wires from the + side of the coil and this issue goes away, the points electrically open and close as normal.

 

[Scott Danforth]

with everything connected (points wire attached to - side of coil), and with the points physicallyView attachment 365513 open, I’m getting 5 ohms of resistance. Not an open.

You are missing the condenser.

Did you replace the condenser? Yes or no?

Check the condenser with the capacitor setting on the meter. If good, then take the meter and set aside

Now connect a dwell meter, and while cranking, what dwell are you getting. Above 32 degrees, open the point gap

Below 30 degrees and close the point gap

 

[Tube1]

You are missing the condenser.

Did you replace the condenser? Yes or no?

Check the condenser with the capacitor setting on the meter. If good, then take the meter and set aside

Now connect a dwell meter, and while cranking, what dwell are you getting. Above 32 degrees, open the point gap

Below 30 degrees and close the point gap

The condenser hasn’t been replaced yet… do you mean physically missing? It’s in the video.

I also discovered that disconnecting the purple wire from the electronic choke removes this shorting issue I’m having.

 

[Scott Danforth]

The condenser hasn’t been replaced yet… do you mean physically missing? It’s in the video.

I also discovered that disconnecting the purple wire from the electronic choke removes this shorting issue I’m having.

Test the condenser (it's a capacitor) if it's shorted, replace it

 

[Tube1]

Test the condenser (it's a capacitor) if it's shorted, replace it

The condenser tested fine. I’m still having the weird shorting issue where when I connect the electronic choke it basically shorts the points together. No clue.

 

[achris]

Electric choke connects to a switched positive, not the points side of the coil...

Chris...

 

[Tube1]

So, had a huge idiot moment. The whole continuity issue was never a problem to begin with. After replacing the points, setting proper gap, and timing, I'm so glad to say the engine runs great! Adjusted the idle and it's right on the money.

I took it out for a lake test and noticed what I thought was a water leak around the rear freeze plug area. After closer inspection it's actually a good size oil leak coming from the valve cover gasket area. Thank god I caught this right off the bat and didn't run the engine soon after. See pics attached. I think it's coming from the valve cover gasket, unless it's somehow leaking from the large hex bolt (?) right underneath the valve cover.

I can't get any gaskets in on time and I really wanted to take this boat out saturday. Would using an oil-grade RTV gasket maker be appropriate for a repair? Forgive my ignorance if that's a bad idea... it was just a thought.

 

[Tube1]

Jinxed myself. I was able to find fel pro 17900 locally. Fingers crossed I can get this patched up in time!

 

[Tube1]

Does anyone have a document showing any torque specs/replacement procedure for the VCG? I read 40 in lbs on this forum but can't find any real documentation. Nothing in my manual.

 

[Scott06]

So, had a huge idiot moment. The whole continuity issue was never a problem to begin with. After replacing the points, setting proper gap, and timing, I'm so glad to say the engine runs great! Adjusted the idle and it's right on the money.

I took it out for a lake test and noticed what I thought was a water leak around the rear freeze plug area. After closer inspection it's actually a good size oil leak coming from the valve cover gasket area. Thank god I caught this right off the bat and didn't run the engine soon after. See pics attached. I think it's coming from the valve cover gasket, unless it's somehow leaking from the large hex bolt (?) right underneath the valve cover.

I can't get any gaskets in on time and I really wanted to take this boat out saturday. Would using an oil-grade RTV gasket maker be appropriate for a repair? Forgive my ignorance if that's a bad idea... it was just a thought.

Oil leak doesnt seem so bad id just take oil out with you to keep topping up and put a rag or paper towl on there to soak it up and wait on the gasket.
did you try snugging up the valve cover a little bit ? Might just be loose and gasket dried out

 

[Scott Danforth]

So, had a huge idiot moment. The whole continuity issue was never a problem to begin with. After replacing the points, setting proper gap, and timing, I'm so glad to say the engine runs great! Adjusted the idle and it's right on the money.

what was the dwell set to? gapping only gets you close.

BTW, a dwell meter would have pointed out that you didnt have a problem

 

[Tube1]

Well guys, I’m back chasing an overheating issue on the 3.0. I pulled what I believe is the raw water supply line (it runs from back of transom/drive area to thermostat) and it’s bone dry while engine is running on muffs (see video). Am I looking at an impeller replacement?View attachment trim.60C08F0C-3251-43E1-8DE0-B3DF6D65F07A.MOV

 

[havoc_squad]

Well guys, I’m back chasing an overheating issue on the 3.0. I pulled what I believe is the raw water supply line (it runs from back of transom/drive area to thermostat) and it’s bone dry while engine is running on muffs (see video). Am I looking at an impeller replacement?View attachment 367600

Possibilities
1. Impeller is toast. If you don't check it every other year or every 100 hours, asking for trouble or be buying a new engine
2. Terrible home water pressure supply on the hose, if so impeller damage is certain.
3. Incorrect installation on water pump impeller on outdrive lower unit.
4. Obstruction somewhere from the outdrive to that supply hose.
5. Water hose that goes from outdrive mounting location to gimble housing near bellows is shot and leaking a lot of water outside the boat before it can get to the engine.

 

[Tube1]

Possibilities
1. Impeller is toast. If you don't check it every other year or every 100 hours, asking for trouble or be buying a new engine
2. Terrible home water pressure supply on the hose, if so impeller damage is certain.
3. Incorrect installation on water pump impeller on outdrive lower unit.
4. Obstruction somewhere from the outdrive to that supply hose.
5. Water hose that goes from outdrive mounting location to gimble housing near bellows is shot and leaking a lot of water outside the boat before it can get to the engine.

Thanks for the reply.

I bought the boat a few months ago and haven’t put even 50 hours on it, so was hoping that I could do a full rebuild in the off season (bellows, etc).

Water pressure is good at home. I ran the boat on muffs several times before this and it had no issues, and exhaust water flow was strong.

Can probably rule out #5 as I see no visible leaks up in that area while engine is running on muffs. I ordered an impeller rebuild kit, time to pull and figure out what happened. Can’t catch a break with this boat… literally just fixed the snapped starter bolt issue 3.0s are infamous for and this happens. Lol

 

[Scott Danforth]

First thing to address on any used boat is new raw water pump, drive service, etc

 

[Scott06]

Well guys, I’m back chasing an overheating issue on the 3.0. I pulled what I believe is the raw water supply line (it runs from back of transom/drive area to thermostat) and it’s bone dry while engine is running on muffs (see video). Am I looking at an impeller replacement?View attachment 367600

i had that exact same symptom on my 3.0, a vane off the impeller ripped off and blocked the water flow out of the pump. Vane was laying flat on bottom of impeller housing

 

[havoc_squad]

Thanks for the reply.

I bought the boat a few months ago and haven’t put even 50 hours on it, so was hoping that I could do a full rebuild in the off season (bellows, etc).

Water pressure is good at home. I ran the boat on muffs several times before this and it had no issues, and exhaust water flow was strong.

Can probably rule out #5 as I see no visible leaks up in that area while engine is running on muffs. I ordered an impeller rebuild kit, time to pull and figure out what happened. Can’t catch a break with this boat… literally just fixed the snapped starter bolt issue 3.0s are infamous for and this happens. Lol

The broken record repeat PSA public service announcement is never ever trust what the previous owners says was serviced and never trust them to be honest on what was hack job/screwed up by them or the owner beforehand.

It is now your problem to manage, not theirs.

 

[Tube1]

Finally got around to pulling the lower unit, and as expected, the impeller was trashed. I’m working on rebuilding right now. Noticed this input shaft coming out of the lower unit has some play, is this normal?

Also, I forgot to put the boat in drive before pulling lower unit. Will that cause issues, or is that only pertaining to when you remove the entire drive?View attachment trim.DACFB80E-97B0-4BC1-B67F-19277D1A24B1.MOV