Mercruiser 3.0 blowed a spark plug

[durabostbay]

Howdy all I have a 96 mercruiser 3.0lx. Was running great till yesterday when the rear spark plug blew out. The threaded part stayed in the head and the guts blew out the center. The engine made a loud pop sound and died. I have replaced all 4 spark plugs but still can't get the engine to start. Please help!

 

[alldodge]

What did the other spark plugs look like?
Are you getting spark?
Do you have fuel?

 

[kenny nunez]

This is a Snap On tool # 8r-20 that I have used many times to remove a spark plug that has blown out. It has never failed.
There similar tools used in the plumbing business that will also work.
Just be sure that the ground electrode is still on the plug body, if not then try to fish it out with a magnet.

 

[durabostbay]

I got the broken plug out with a easy out. Installed 4 brand new plugs today. Carburetor has fuel and all 4 plugs spark when I remove and ground them. Also all 4 plugs are wet when I remove them. Boat was running close to wide open throttle when the plug blew. Got it to hit a few times earlier today but no where near close to running.

 

[dubs283]

Also all 4 plugs are wet when I remove them.

the engine is flooding

to clear the flood, set the throttle to wide open and crank the engine over. do not pump the throttle, just set it to wide open. when the engine fires pull the throttle back to a reasonable rpm

if the engine wants to die out when throttling back there is most likely a carburetor issue with flooding and could use a rebuild

 

[alldodge]

Need a carb rebuild

 

[durabostbay]

Is it possible that the sudden spark plug blow out under load could mess up something in the carburetor? I've installed new plugs, wires, cap, and button. I did not see spark with the new button so I put the old button back in and see spark again. I also checked my fuel for water and it is good.

 

[alldodge]

Is it possible that the sudden spark plug blow out under load could mess up something in the carburetor?

Don't see how that would happen

Maybe the rotor didn't go all the way on. If it was just a tad to high, the distributor would turn, but the rotor may not, get hung up inside the cap. Check the rotor closer to see if something looks wrong

 

[durabostbay]

This thing is really kicking my butt. I've thought it was flooded and held the throttle wide open while cranking for awhile and nothing. Ive also poured gas down the carb and tried starting fluid. I can't get it to even sputter. Im leaning towards maybe it's jumped timing. What do these engines use for timing and how can I check it?

 

[alldodge]

Then you have a spark issue, or your flooded really bad

Run through this

 

[durabostbay]

Thanks for the trouble shooting guide. I've seen a couple of post about the gry tachometer wire shorting out. Where do I find this wire at on the engine?

 

[alldodge]

Thanks for the trouble shooting guide. I've seen a couple of post about the gry tachometer wire shorting out. Where do I find this wire at on the engine?

Gray comes from Neg side of coil and goes to the Tach thru the 10 pin motor connector. In most cases, just disconnect from the Tach to verify its not the problem

 

[durabostbay]

Ok, I have unhooked the wires from the back of the tachometer and ohmed the grey wire to ground and it is not grounded. Still wont crank. Had a friend look at it and he thinks the spark looks weak and sporadic. I thought the same thing but shrugged it off thinking I just didn't have the spark plug grounded good. I've ohmed the coil. Primary 12v side is .2 to .4 ohm and on the secondary side I get no reading at all. I'm thinking I should see something on the secondary side. What yall think?

 

[alldodge]

Did you run through the test in post 10 ??

Coil test
https://www.aa1car.com/library/ignition_coils.htm

 

[durabostbay]

I made it to the part about the white/red bullet connector on the distributor. I don't see a white/red bullet connector on my distributor. Im on vacation this week and my boat is anchored in the lake so I don't have all the things I need to go through the whole test nor ideal working conditions as I have to swim to the boat. I got someone lined up to tow me back to the ramp tomorrow. Ill let yall know how it turns out.

 

[dubs283]

I made it to the part about the white/red bullet connector on the distributor. I don't see a white/red bullet connector on my distributor.

that troubleshooting guide is for a thunderbolt ignition. as far as i know mercury never used the thunderbolt on a 3.0 L.

your ignition system is most likely the delco EST system, completely different from the thunderbolt

 

[alldodge]

that troubleshooting guide is for a thunderbolt ignition. as far as i know mercury never used the thunderbolt on a 3.0 L.

your ignition system is most likely the delco EST system, completely different from the thunderbolt

Good point dubs, my bad, so forget the TBV guide. Never did see a serial number

EST trouble shooting guide

 

[durabostbay]

Yes Delco est is what I have. And the pics in this guide look exactly right. Thanks for the help. I said I won't going to work on the boat on my last day of vacation but I might can spare a little time for these test.

 

[durabostbay]

Ok guys, I've performed all the test in the above troubleshooting guide. Everything checks out like it should. The engine will still not start. For fun I hooked my timing light up and tested all 4 wires and just like I saw while on vacation the spark is erratic. #1 always gives 1 spark when the engine first starts to rotate then no sparks for a few rotations then 2 or 3 sparks and the cycle repeats. #2 and #4 do basically the same as #1 but #3 never sparked at all. So if the ignition and pick up coil check good per the troubleshooting guide what's next the ignition module? Is there a troubleshooting guide for the ignition module? Are there any known symptoms of a bad ignition module?

 

[durabostbay]

I'll add although the pickup coil tested good it does not look healthy to me. Some of the outer "insulation" of the coil windings has broken down and fell off.