How often do coils go bad?

[Still LauCo]

On my 300 DA, (5.7EFI) I had been having intermittent trouble when at idle the stbd engine would "drop out" and quit... It would always start back up, but was a 50/50 proposition that it would quit again during the docking process.

Anyways, a friend of mine who is a mechanic said the coil looks like it is shot, just wondering if this is a common occurence and potentially the issue. We just tested the coil by "bumping" the motor, but got no spark... So we are going to replace it.

I really won't be able to validate that this is the fix until April when it gets dropped in the water.
Thanks!

 

[Sundancer]

Most last quite a while, but I had one in an old car that only lasted about 6 mos. I had swapped it out and was SURE it was brand new and couldn't be the culprit! Changed it and problem solved!! I was TICKED!!!

 

[Fun Times]

You can always test your ignition system with the list below.

But Keep in mind that there is a chance that your coil is fine and the problem might be within the shift interrupter switch adjustment do to a bad shift cable, I say that because you said the engine dies while docking, And that means a lot of shifting.

 

[BonBini]

Coil failures are pretty rare but they do happen. Coils are one of those components that it's more cost effective to replace it that to have it tested.

Intermittent coil failures are typically internal shorts, external case cracking or most common ... corroded lead terminal.
Related symptoms are commonly hard starting due to weak spark or intermittent misfiring due stray shorting voltage.

An easy test of the secondary ignition system is to mist some water from a spray bottle over the entire system at night and visually look for stray voltage leaking from coil, dist cap and wires. (I shouldn't have to say be careful around running machinery with loose clothing exc....)

Having said all that. Based on your docking symptoms. I'm more with Boat Tech on the shift interrupt switch area.

 

[Still LauCo]

Thanks for the responses. The shift interupt appears to be ok. It doesn't drop out while shifting, but when running at idle, whether I am shifting or not. The coil has some "goop" running down the side of it, and we are going to replace it and hope that it runs perfect again at launch!

 

[Redhook98]

Usually a coil will go bad at higher RPMs first. It starts to break down and can not keep up witht he higher RPMs.

When I had a similar problem with mine, it turned out to be the IAC valve. Depending on how much you "bump" the motor, you may not see any spark at all, with or without a good coil. Pull the IAC and make sure it is not stuck. (takes all of 2 minutes to do this).

Have you tried to "bump" the other motor and get spark from it? I have 27 years on the coils on my "new" boat and they still work great. Coils do not often break-down. And when they do, it starts at the higher RPMs first.

Just sayin'....

 

[Still LauCo]

Usually a coil will go bad at higher RPMs first. It starts to break down and can not keep up witht he higher RPMs.

When I had a similar problem with mine, it turned out to be the IAC valve. Depending on how much you "bump" the motor, you may not see any spark at all, with or without a good coil. Pull the IAC and make sure it is not stuck. (takes all of 2 minutes to do this).

Have you tried to "bump" the other motor and get spark from it? I have 27 years on the coils on my "new" boat and they still work great. Coils do not often break-down. And when they do, it starts at the higher RPMs first.

Just sayin'....

That's interesting information. The whole thing started about a month before season end, when I was at cruising speed and I lost power to that motor. I came in on one, and when I got back to the dock it restarted. I figured it was just bad gas. Then I had the above mentioned idle problems, and then lost the motor again when I was coming in for the haul out. I'll cross my fingers, as compression test and visual inspection came out ok.

 

[Redhook98]

That's interesting information. The whole thing started about a month before season end, when I was at cruising speed and I lost power to that motor. I came in on one, and when I got back to the dock it restarted. I figured it was just bad gas. Then I had the above mentioned idle problems, and then lost the motor again when I was coming in for the haul out. I'll cross my fingers, as compression test and visual inspection came out ok.

The IAC valve issue would not effect operation above 1500 RPM or so (i.e. at cruising speeds). Could be the coil... The good thing is you have another good motor with good parts on it right next to ya! Makes for real easy troubleshooting.

Take a resistance reading of your coil between the + and - lugs (with key in OFF position). Then compare it to to your other motor. It will be more obvious if both were hot, but that does not seem possible right now.