No spark - 1987 3.0 mercruiser

[Tjburden]

New to the forum.
Have a now spark and have been following Don S adult only.



***Checking for spark***
fully charged battery new plugs last fall (winterized). Boat sat for 12 months 2016-2017. Had mechanic do complete tuneup, new cap rotors, plugs and wires, fuel drained from tank. Good fuel delivery and treated fuel
2019 I had no start the wire from the coil to distributor was bad had to replace.

i winterized 2019 and plugs were black/sooty so I replaced.

now no start

- Spark test at the coil was negative

- Disconnect the ONLY grey wire from the (-) side of the coil, kept all others connected. Still no spark

- With all wires diconnected from the coil, check for continuity between the tower and both (+) and (-) posts on the coil. no continuity -replaced coil. Repeated previous two steps still no spark

- With the ignition switch at the helm in the "on/run" position. I have 12 volts not 4-9 at the coil (+) I did not put on jumper wire as I have to many volts.

- If there is 4-9 volts (+), there is proper voltage at the coil. I have to many

- Follow the purple resister wire to wiring harness coil to the round connector, alternator and choke from the coil (+) connection - inspect the wire for damage/corrosion. Did not see any damage.

- If the resistance wire that has a resistor built into it preventing too much voltage at the coil - how to I correct this.

I cleaned the connection at the harness and re-installed also put the grease recommend by Don

i have 12 volts at the key. I don’t have the remote start switch.

I’ve disconnected the coil from the boat to make sure it does not get damaged.

any help would greatly be appreciated.

 

[achris]

Hello Tjburden and :welcome: aboard.

First up, what ignition system are you working with? That era of 3 litre could have Points, DDIS or EST... Each is very different, and has it's own troubleshooting method.

Also, please re-read what you type before posting. I suspect you're using a phone, and that it's 'auto-filling' words, because there's a few lines up there ^^^ that don't make any sense...

Cheers and thanks,

Chris..........

 

[Tjburden]

Thanks Chris - yes working off a device and will pay attention.
I have Points

 

[achris]

Points are the easiest to troubleshoot.

You should have 2 wires on each side of the coil. On the + side, a purple (your 'resistance' wire) and a purple/yellow (to the starter motor). On the - side you should have a grey (to the tacho) and a black (to the points in the dissy)...

Measuring voltage at the coil + needs to be done with the points CLOSED, or all you will see is battery voltage (12v).

I would remove the purple/yellow and the gray wire and start troubleshooting from there. Get an old spark plug and put it in the HT lead that goes to the cap centre terminal, lay the plug on the engine block (this removes the cap and rotor from being part of the problem). Also, remove the cap from the dissy so you can see the points opening and closing. I would also remove the spark plugs so the engine spins faster. When you crank the engine, you should see a small spark between the points contacts... If you don't see that, you have a primary side problem. With the points closed, measure the voltage on the + side, should be about 7v. On the negative side should be 0v.

Chris.........

 

[Tjburden]

Thanks Chris - some great pointers. I will give this a try. My purple/yellow and purple resistance wire share the same ring terminal. I will need to make a bypass wire. Not at the boat, but does this purple/yellow come from the starter solenoid?

 

[achris]

Thanks Chris - some great pointers. I will give this a try. My purple/yellow and purple resistance wire share the same ring terminal. I will need to make a bypass wire. Not at the boat, but does this purple/yellow come from the starter solenoid?

Ah, crimped together. Ok. Either cut one off and add a crimp to that lead, and they'll be separate from now on, or just leave it there. Yes, from the starter solenoid.

Chris....

 

[Tjburden]

Ok I removed the purple/yellow wire, gray wire and payed plug of the coil wire. I had no spark. I measured the volts on the coil (+) side and they are 12 volts and 12 volts on coil (-) with points closed.

 

[Scott Danforth]

DIY sticky at top of forum has a guide on points ignition

It is the simplest ignition system in the world. Essentially a mechanical switch turning the coil on and off

 

[achris]

Ok I removed the purple/yellow wire, gray wire and payed plug of the coil wire. I had no spark. I measured the volts on the coil (+) side and they are 12 volts and 12 volts on coil (-) with points closed.

12v on coil '-' with the points closed? Clean the points contact faces.

 

[Tjburden]

Ok - thanks. I will take a look at the points and clean.

ty

 

[BigWeakSauce]

Call me crazy but isn't the voltage issue here typically indicative of a bad ignition coil on these systems?
And a short cut to checking the points for spark, with the key "on" take a screw driver to the wired end of your points and if it sparks on your screw driver it will certainly spark when shifting with the cam (unless its dirty/corroded which is easily visible). Sometimes hard to see that spark in the daylight from the helm of your boat while cranking the engine.
In my opinion if you have new points, condenser, rotor, cap, and good wiring, and are getting a bad voltage read at the coil, then swap the coil.

 

[Scott Danforth]

Call me crazy but isn't the voltage issue here typically indicative of a bad ignition coil on these systems?
And a short cut to checking the points for spark, with the key "on" take a screw driver to the wired end of your points and if it sparks on your screw driver it will certainly spark when shifting with the cam (unless its dirty/corroded which is easily visible). Sometimes hard to see that spark in the daylight from the helm of your boat while cranking the engine.
In my opinion if you have new points, condenser, rotor, cap, and good wiring, and are getting a bad voltage read at the coil, then swap the coil.

only 3 out of about a million changed coils is actually bad. so no, dont swap the coil unless you have done the proper troubleshooting.

points need to be filed to clean them every year if they sit. even new points need to be filed. that is even in the mercruiser manual

simply taking a wire with an alligator clip to the negative side of the coil and touching and releasing from ground will trigger the coil to fire.

 

[achris]

...simply taking a wire with an alligator clip to the negative side of the coil and touching and releasing from ground will trigger the coil to fire.

if the points are in the open position...

 

[achris]

... and are getting a bad voltage read at the coil, then swap the coil.

:facepalm:

He's getting 12v on the coil negative with the points closed. That's not a 'bad voltage reading'. That indicates the points aren't closing electrically (dirty/corroded).

It's such a simple circuit, how can people get this so wrong!

 

[Scott Danforth]

shhhhhhhh achris I bought stock in coils.....

 

[Tjburden]

Ok -wow. Thanks everyone. Just got home from work. I cleaned points. Same results.
the points, condenser and rotor are three years old. The coil is new, two days. You coil stock went up

I’ll clean one more time - and check at night here on west coast. The run voltage test A & B. If that fails should I just replace points condenser and rotor at this point.

ty

 

[Tjburden]

Cleaned some more. Not sure what clean is. But Yea : points open wire on coil(-) spark from wire and plug from HT lead.
Voltage with points closed coil (+) 6 volts and coil (-) <1 volt, but some. With points open 12 volts on both side. I also noted the resistance wire was warm, but not hot. I will reassemble and see if she starts tomorrow.

ty

 

[Scott Danforth]

are you fully assembling the rotor and cap to check for spark? please list the steps in full detail.

also, are you verifying the dwell with a meter? and then setting timing?

 

[Tjburden]

Fully assembled - started right up. Like she use too. Thanks everyone. Learned a lot.

ok - placed ring connector on purple yellow wire. And returned to coil (+) with resistance wire. Returned gray wire to coil(-). Before I started checked point res. Was good
placed rotor and cap. Fastened. Started right up.
dwell angel 15 degrees if I’m reading it right. Again thanks. Feels good when everything works out.

 

[achris]

Great! I love happy endings.

Dwell should be 28° to 34°. At 15° it means the gap is too big. Set them to 22thou, that should get the dwell close. And when you change the gap/dwell, you need to reset the timing after.