454 Magnum electrical issue

[32Outlaw]

I have a 1994 454 Magnum that is having ignition issues and will not turn over.

We have taken everything from the Starboard motor and swapped it to the Port motor with no luck. Swapped distributor, ignition control module, coil, wires, ignition switch, etc.

Any ideas what I could try next? I had someone suggest that the harmonic balancer could have slipped or be bad, is this a possibility? Can an issue with the Mercathode galvanic corrosion system cause no spark? I am not sure how to test this.

Any help anyone can give is very much appreciated!!

Thanks,
Chris

 

[Bt Doctur]

Re: 454 Magnum electrical issue

"turns over" just means the motor will turn or spin or crank or rotate
"does not start" is totally differtent.
what kind of ign and module
do you have 12V at the + side of the coil
Alpha drive= check shift interupter

 

[32Outlaw]

Re: 454 Magnum electrical issue

It just turns and turns, no fire.

Thunderbolt ignition.

No, there is zero voltage at the '+' side of the coil.

Bravo drives.

 

[Don S]

Re: 454 Magnum electrical issue

No, the Mercathode is not the problem. You could also take the harmonic balancer off and the engine would still run, it has no effect on spark.

You SHOULD have the Thunderbolt IV ignition, and a Bravo drive. Merc didn't use the Alpha drive with a 7.4 after 88.

Do you have a lanyard safety kill switch on your engines? Do you have power to the + terminal of the coil with the key in run? If so, check for voltage while the starter is cranking the engine over.

If you do have power to the coil, try disconnecting the tachometer gray wire from the coil - terminal and try it.

( EDIT: You posted while I was typing)

 

[Bt Doctur]

Re: 454 Magnum electrical issue

run a jumper from the + battery to the + coil.
do the gauges move?
will it now run or atleast have spark?

 

[Don S]

Re: 454 Magnum electrical issue

No, there is zero voltage at the '+' side of the coil.
.

Check for voltage on the ignition switch on the purple wire with the key on.

Just to make sure it will run, jumper wire from the coil + terminal to the battery positive terminal and start it. Remove jumper to shut it off.

 

[32Outlaw]

Re: 454 Magnum electrical issue

The purple wire on the ignition switch has voltage.

When I hook a jumper from the + battery to the + coil it will start.

 

[Don S]

Re: 454 Magnum electrical issue

Kill switch or a bad connection between the switch and the coil.

 

[32Outlaw]

Re: 454 Magnum electrical issue

Sorry, I swapped the kill switches from port to starboard and that did not fix it so that too is eliminated.

Any idea where to start when looking for the bad connection?

Thanks for all your help Don and Bt!

 

[Bt Doctur]

Re: 454 Magnum electrical issue

check under the dash for a harness plug,may or may not have one. purple goes thru the harness back to the engine wiring thru a cannon plug, a main harness plug usually found on the engine or riser. loosen clamp,pull apart and check for corrosion.

 

[Don S]

Re: 454 Magnum electrical issue

Any idea where to start when looking for the bad connection?

Start at the switch, and work your way back to the engine till you run out of power.

 

[32Outlaw]

Re: 454 Magnum electrical issue

Thanks again for your help! I will be going to the lake this weekend to try and track down the connection, hopefully I can find it!