Help with diagnosis

[AmericanHoney]

Just looking for help on figuring out an issue and wanted to see if what I was thinking made sense. I'm a newbie to boating and hardly any experience with engines.

Little over a week ago I noticed when traveling slowly with my boat, a slight stutter. It was almost unnoticeable and I thought maybe I was imagining it, but after it happening a couple times I was certain something didn't seem right. Initially I thought maybe it was fuel related. So I got some cleaning additives and made sure the vent hose wasn't plugged. After doing that I took it out again and the problem was still there, but this time I heard what sounded like a spark jumping, so I turned right around. Checked it out at the dock and thought the spark sound was coming from the distributor cap, couldn't see it though. So I replaced the cap and rotor yesterday and took it out again, but the problem and the spark sounds was still there. This time though when I looked for the spark I was able to see it, since it was overcast and a bit darker.

The spark was jumping out of the end of the wire on the ignition coil. I plan on replacing the wire and will most will also replace the coil, which I believe should fix the jumping spark. But my question is does the symptom of the boat slightly stuttering sound like it should be related to the jumping spark??

The boat never stalled and I really only notice the issue when going slow, but that's not to say it doesn't happen when opened up, because it is so slight. Summer is running out, so I'd really like to get this problem buttoned up and would be grateful for any opinions or advice.

The engine is a 1983/84 260 HP 5.7l Mercruiser with Thunder Bolt ignition.

Thanks in advance.

 

[sethjon]

Re: Help with diagnosis

Just looking for help on figuring out an issue and wanted to see if what I was thinking made sense. I'm a newbie to boating and hardly any experience with engines.

Little over a week ago I noticed when traveling slowly with my boat, a slight stutter. It was almost unnoticeable and I thought maybe I was imagining it, but after it happening a couple times I was certain something didn't seem right. Initially I thought maybe it was fuel related. So I got some cleaning additives and made sure the vent hose wasn't plugged. After doing that I took it out again and the problem was still there, but this time I heard what sounded like a spark jumping, so I turned right around. Checked it out at the dock and thought the spark sound was coming from the distributor cap, couldn't see it though. So I replaced the cap and rotor yesterday and took it out again, but the problem and the spark sounds was still there. This time though when I looked for the spark I was able to see it, since it was overcast and a bit darker.

The spark was jumping out of the end of the wire on the ignition coil. I plan on replacing the wire and will most will also replace the coil, which I believe should fix the jumping spark. But my question is does the symptom of the boat slightly stuttering sound like it should be related to the jumping spark??

The boat never stalled and I really only notice the issue when going slow, but that's not to say it doesn't happen when opened up, because it is so slight. Summer is running out, so I'd really like to get this problem buttoned up and would be grateful for any opinions or advice.

The engine is a 1983/84 260 HP 5.7l Mercruiser with Thunder Bolt ignition.

Thanks in advance.

I think so. When the spark doesn't go to where its intended its temporary connection break and the way you describe it could definitely happen. When you replace the wire, replace al lof them because others may be ready to break down as well.

 

[John_S]

Re: Help with diagnosis

Yes the jumping spark could be your stuttering. A spark jumping within the closed confines of engine compartment is very dangerous. The new lead and coil should fix.

 

[libellav15]

Re: Help with diagnosis

new lead only i would say

i think if there is evidence of a good spark albeit going to the wrong place due to lead breakdown - which as has been mentioned is VERY dangerous in a marine setup - then the coil is obviously up to the job

or am i missing something? any oil coming out of the coil?

 

[Rocky_Road]

Re: Help with diagnosis

If this were mine, I would be trying some dieletric grease on the wire ends and boots.

Happy boating!

 

[achris]

Re: Help with diagnosis

If the boat's being used in a salt environment then you could have some salt on the coil which would lead to a spark jumping to ground from the tower instead of going to the distributor. I would replace the lead and clean down the coil, also a light coat of corrosion guard wouldn't hurt....

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

 

[AmericanHoney]

Re: Help with diagnosis

Thanks guys.

It's not in a salt water enviroment, but the spark does seem to be jumping down from the tower to the ground. I will try a new lead first and clean the coil and see if that does the trick.

Yeah, when I first thought I heard a spark in the engine compartment I couldn't get back to the dock fast enough.

 

[achris]

Re: Help with diagnosis

Look for tracking or a hairline crack in the top of the coil... Replace it if you find anything...

Chris.......

 

[EddiePetty]

Re: Help with diagnosis

Look for tracking or a hairline crack in the top of the coil... Replace it if you find anything...

Chris.......

....and if you can't see tracking or a hairline crack (if the spark jump continues after lead replacement), dust the dry coil with plain flour or baby power. If an arc continues, the powder will burn and leave behind a trace line similar to a pencil mark. [An old timer (yeah, older than me) showed me this trick on a distributor cap that no one could find a crack in.]

 

[achris]

Re: Help with diagnosis

....and if you can't see tracking or a hairline crack (if the spark jump continues after lead replacement), dust the dry coil with plain flour or baby power. If an arc continues, the power will burn and leave behind a trace line similar to a pencil mark. [An old timer (yeah, older than me) showed me this trick on a distributor cap that no one could find a crack in.]

This one is going in my notebook... Nice trick!!!

Chris..........

 

[libellav15]

Re: Help with diagnosis

talc to show up arcing tracks

top tip mate - i too will be keeping that one in the grey matter

 

[libellav15]

Re: Help with diagnosis

hey eddie

did he put powder inside the dizzy cap - or over the outer?

 

[Eric 3.7LX Alpha 1]

Re: Help with diagnosis

hey eddie

did he put powder inside the dizzy cap - or over the outer?

definately keep the inside clean and dry. all outside only

 

[libellav15]

Re: Help with diagnosis

definately keep the inside clean and dry. all outside only

just checking

d'oh :redface:

 

[rbh]

Re: Help with diagnosis

we had an issue once were the plug wire had come off of the plug, you could hear the snap of spark but it was from the top of the coil to the ground lug.

I am guessing that since the plug end had no place for the spark to jump to it took the second easiest path to ground and that was the coil end???

And Eddie great trick, must remember that one.

 

[EddiePetty]

Re: Help with diagnosis

.....we had an issue once were the plug wire had come off of the plug.......

Back in my dirt modified racing days (daze), simply the roughness of a given track, g-forces and just maybe the occasional 'love tap' from a competitor would be enough to knock a less-that snug plug wire of either the distributor or a spark plug. That same 'ol fossil fart showed me how to smear dielectric grease in all the rubber boots to form an air tight, almost suction seal to the terminals. That was back in the sixties. Haven't had a plug wire come off since in everything from lawn mowers to modifieds.

 

[rbh]

Re: Help with diagnosis

Back in my dirt modified racing days (daze), simply the roughness of a given track, g-forces and just maybe the occasional 'love tap' from a competitor would be enough to knock a less-that snug plug wire of either the distributor or a spark plug. That same 'ol fossil fart showed me how to smear dielectric grease in all the rubber boots to form an air tight, almost suction seal to the terminals. That was back in the sixties. Haven't had a plug wire come off since in everything from lawn mowers to modifieds.

Thanks Ed, but was my big foot 5 minutes before that popped it off. :redface:

 

[ragtop]

Re: Help with diagnosis

Wow How bizarre, I was searching thru the posts for the exact same thing, but I did not find my arc until after being towed in by a fellow boater, mine was also arcing from neg post to bottom of coil tower, I didn't find this out until returning home and found it by accident when starting to troubleshoot.and my coil past all the tests, I even tried to put a piece of rubber between the tower and neg post, it started temp until it put a hole in the rubber, so I replaced the coil and everything is great now, was really starting to wonder if it was a points problem, it wasn't,,,,good luck