4.3 l keeps blowing ignition fuse

[vikesfan24]

I have a 2005 4.3l mercruiser. At rpm above 3000 I blow the ignition fuse. I have checked and taped any bare wires. I replaced the coil. I disconnected the tachometer at the dash. I ran it without the alternator connected. Problem stayed through all of this. I'm at a loss of what to do next. Any suggestions would be greatly appreciated!

 

[solar7647]

Check your spark plug wires, maybe getting a short from them because of cracking or dry rot. Best way I know is to run your hand over them while it's running. You will deff feel it, might not the smartest way but it works.

Also check the ignition wire, it's normally purple. The insulation could be bad and once it's warm and running at a high rpm could be opening up a defect and allowing a ground to the block.

It's definitely something shorting to ground that should not be.

 

[Paintman1960]

Check your spark plug wires, maybe getting a short from them because of cracking or dry rot. Best way I know is to run your hand over them while it's running. You will deff feel it, might not the smartest way but it works.

Also check the ignition wire, it's normally purple. The insulation could be bad and once it's warm and running at a high rpm could be opening up a defect and allowing a ground to the block.

It's definitely something shorting to ground that should not be.

LMAO !!

 

[vikesfan24]

Appreciate the response, but I've checked all wiring and even ran it in the dark to see if I could see a spark anywhere in the engine compartment when the fuse blew but nothing.

 

[achris]

TKS carb?

 

[vikesfan24]

Yes

 

[achris]

You have a faulty diode. Don't bother with Merc's 'marine taxed' diode either. Nip down to your local electronics shop and ask for a rectifier diode, around 3A (something like a 1N5404). If you have even a modicum of electrical knowledge, it'll be easy to replace.

Chris.......

 

[vikesfan24]

Thank you, definitely worth a try. I can test it tomorrow. Have you heard if this is common? The TKS diode service bulletin I had read said it caused the engine to keep running or be hard to start at warm temp, but didn't mention a blown fuse. But I'm willing to try the diode. Thank you!

 

[vikesfan24]

The diode is shorted both directions. If I try running the boat now without the diode in, would that be a good test? Wondering if I ran it like that and didn't blow the fuse if that would prove the diode is the culprit?

 

[achris]

No, you need the diode to get the module in the carb to heat up...

 

[vikesfan24]

Test

 

[vikesfan24]

After replacing the diode with one I had on hand it seemed to work until I quickly hit about 3800 rpms then the ignition fuse blew again. I unhooked the tach and was able to hit 3800 quickly and the fuse didn't pop. My question now is how high do I dare run on water muffs in the driveway? Everytime I run to the lake to test it's 2 hours round trip!!

 

[vikesfan24]

Doesn't look like it is the tachometer. When running with the diode out and the temperature switch disconnected I don't blow the fuse. Does anyone know how to test the switch? It has a fuel line laying right on top of it that looks like it may have rubbed the wires some. However it shows an open on the switch at 175deg. Is that right?