91 Mercruiser 7.4l Bravo One Tripping Circuit Breaker

[mstrianse]

I can start my boat for approximately 10 to 20 seconds and then the breaker next to the ignition key trips. I just had the engine out to replace the coupler. Logical area for a pinched wire would be engine bay but upon multiple investigations everything appears to be in order. I started boat with alternator disconnected and had same result. Batteries are fully charged. Any ideas or suggestions with this issue?

 

[alldodge]

Does it pop the breaker if key is turned ON but motor is not started?

 

[mstrianse]

No, it only pops breaker when engine is running. Upon start up tach will work but then has no reading, even if I give the engine throttle in neutral

 

[alldodge]

Upon start up tach will work but then has no reading,

This could be good

Disconnect the gray wire off the +side of the coil.

When disconnection the ALT, did you disconnect the 2 small wires (red/purple and purple) or just the orange one?

 

[mstrianse]

I only took the orange one off the ALT. I have 2 purple wires on positive side of coil.

 

[Bondo]

I only took the orange one off the ALT. I have 2 purple wires on positive side of coil.

Ayuh,..... Welcome Aboard,...... I think AD hit the wrong key on his keyboard,.....

Disconnect the gray wire from the (-) tiny terminal on the coil,......

 

[alldodge]

I only took the orange one off the ALT. I have 2 purple wires on positive side of coil.

Remove the 2 smaller leads, they are the ones which pull from the ignition side

Disconnect the gray wire from the (-) tiny terminal on the coil,......

Yep - side

 

[mstrianse]

OK, I will take wires off ALT. Two wires on neg coil side are tan. I'm having trouble uploading photo. I believe the tach wire comes off module plug.​

 

[mstrianse]

Here is pic of coil wires.

 

[alldodge]

OK, I will take wires off ALT. Two wires on neg coil side are tan. I'm having trouble uploading photo. I believe the tach wire comes off module plug.

Just use the default font, much easier to read

The 2 wires on the - side, one will go to the distributor and the other will go inside the harness, remove the one going into the harness

 

[mstrianse]

Thank you, I will do what you suggest, start engine and report back.

 

[mstrianse]

ALT only has orange and black wire. Wires on - side of coil one comes out of harness other goes to plug to module. Wires on distributor both also go to plug on module. What do you suggest?

 

[alldodge]

ALT only has orange and black wire. Wires on - side of coil one comes out of harness other goes to plug to module. Wires on distributor both also go to plug on module. What do you suggest?

Both your ALT and distributor does not add up for a 1991 7.4 (454).

What is your engine serial number?

 

[mstrianse]

Here is the engine number off the cover of the carb 0D446001
When I purchased the boat 5 years ago the previous owner said the boat had a new engine installed in it.
You are correct the diagram does not match up. For example the oil pressure sending unit has 2 red wires on it.

 

[alldodge]

New engine changes things. Post a pic of the motor from the top?

Assuming its still a carb motor and not EFI, then disconnect the fuel pump . The motor will run for several minutes before all the fuel is used up.

 

[mstrianse]

It is still a carb motor. I have attached pictures that I had in my phone. I can take more when I get home.

 

[alldodge]

That's a TB distributor, and the module is a TB4. I'm figuring the wires have lost there color thru time and heat. Remove the wire the arrow is pointing to. The other one goes to the module

 

[mstrianse]

Just want to be clear, remove wire that goes to harness. Should I take any other wires off before starting the engine?

 

[alldodge]

Should I take any other wires off before starting the engine?

Only if needed to remove the wire going to the harness, the others need to stay connected. Were trying to find out if the tach is drawing to much current.

Never know you may actually have a bad coil, and this would be the 3rd I've ever found

 

[mstrianse]

Breaker tripped in about 10s. I put a new coil on but put old back to make sure it wasn't new coi .