Frustratingly simple question - Mercruiser Ignition Coil 392-805570-1

[drryan]

I have a NauticStar 2007 Deck boat.
Engine Mercruiser 4.3L Model MCM 4.3 LITRE (OW625493) Mar 2006
The problem is that it is knocking and losing power when hot.
I have been told to replace the Mercury Ignition Coil 392-805570-1.
The problem is that finding an exact match to this number is way harder than it should be. I find many coils that have the same numbers up to the last when they say 392-805570"A"1.
Are these interchangeble? (This is the simple question.)
Also is this a Thunderbolt ignition system? If so I am assuming it is a Thunderbolt IV system.
With lots of respect and appreciation,
drryan

 

[drryan]

I have a NauticStar 2007 Deck boat.
Engine Mercruiser 4.3L Model MCM 4.3 LITRE (OW625493) Mar 2006
The problem is that it is knocking and losing power when hot.
I have been told to replace the Mercury Ignition Coil 392-805570-1.
The problem is that finding an exact match to this number is way harder than it should be. I find many coils that have the same numbers up to the last when they say 392-805570"A"1.
Are these interchangeble? (This is the simple question.)
Also is this a Thunderbolt ignition system? If so I am assuming it is a Thunderbolt IV system.
With lots of respect and appreciation,
drryan

Replying to my own post after reading the great sticky article on Thunderbolt ignition systems. Based on that I am now assuming this is a TB V ignition system. Still have the same question however.

 

[Bondo]

Ayuh,..... Who told you to replace the coil, 'n why,..??

I suggest you check the contents of the fuel filter in a clear vessel, for anything but clean fresh gasoline,.....

 

[Bt Doctur]

The problem is that it is knocking and losing power when hot.

This DOES NOT sound like an ignition problem. But if you want to replace the coil use an "Accell "brand v coil

 

[drryan]

Thank you for the responses. Probably should have said that I have replaced the fuel filter, checked the fuel vent both while it was knocking (took the cap off) and took it off and blew through it, new gas. I need to use the boat the 2nd or 3rd week in July and all the mechanics around here have a 5 week back up and one of them said to try to coil. I've read a lot of the posts on this "hot" knocking and figure the coil was easy that is until I tried to find the right part.
Thanks again.

 

[Scott Danforth]

did you check the contents of the fuel filter in a clear container. this is to check to see that you have pure fuel, and not water in the fuel. it has less to do with the filter.

if the fuel separates, pump out the tank and start over.
if the fuel is cloudy, pump out the tank and start over

its never the coil (ok, 3 out of one million coils changed are actually bad, however that is 99.99997% probability its not the coil)

 

[drryan]

Great question. Dumped the fuel/water separating filter contents into a container and it was not cloudy but markedly yellow which I am told could be a sign of water. Ran dry and replaced with good fuel. May need to change the filter again though. Curious as to why it only starts knocking about the 2nd hour out on the lake. Cranks fine and runs well but after extended runs starts knocking. Thanks for the question and response.

 

[Bt Doctur]

Put a timing light on it .poor fuel or over advanced timing would make that sound too

 

[drryan]

Thanks will do that.

 

[cfeaster]

Did you ever find a solution to your engine cutting out after running for awhile? I have a similar situation where the boat runs great for at least a half hour and will then start cutting out, backfiring, and losing power if I’m above 1500 rpm’s but even then, it runs fine 1500 rpm’s and lower. I’ve changed the water separator, plugs, and wires. The cap and coil are really old so I’m considering replacing them. I have a 2005 Stingray with the 5.0l Mercruiser.