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Runs on start, but not on run.

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Msanders13

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Hey all, new to the site and have a few years unset my belt as a boat owner, enough to know when I need help. I'm a novice at best, so be gentle.

So, this season's issue is getting the darn thing to stay running. As I said, when the ignition is on start, it runs like normal but the instant I let it spring back to run, dies. I replaced the ignition switch, no change. I have never done anything electrical, but I do own a volt meter. Can anyone give me some direction on what/ where to start running down the failure? I'm decent with motors, not so much electrical. I have a 5.0 Cobra with no manual for wiring diagrams etc. And not really sure how to proceed. Thanks for your time.
 
Msanders13 said:
Hey all, new to the site and have a few years unset my belt as a boat owner, enough to know when I need help. I'm a novice at best, so be gentle.

So, this season's issue is getting the darn thing to stay running. As I said, when the ignition is on start, it runs like normal but the instant I let it spring back to run, dies. I replaced the ignition switch, no change. I have never done anything electrical, but I do own a volt meter. Can anyone give me some direction on what/ where to start running down the failure? I'm decent with motors, not so much electrical. I have a 5.0 Cobra with no manual for wiring diagrams etc. And not really sure how to proceed. Thanks for your time.
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This may or may not apply to your 5.0L w/ Cobra drive.

Depending on the year model and type of ignition system, your ignition system may include what we call a "start-by-pass" circuit.
When the starter motor is engaged, battery voltage is reduced, causing the resisted voltage to the coil to become further reduced (reduced to the point of a weak spark).

The Start-by-Pass circuit supplies a full 12 volts to the ignition coil by way of momentarily circumventing the ballast resistor.
During cranking the coil receives closer to 12 volts (ensuring a good spark).

Once the starter motor has been disengaged, the system reverts to resisted voltage.

So...... If equipped with a ballast resistor, and if the ballast resistor has gone bad, it may explain why the engine runs with the key switch held in the "start" mode.
In other words...... the engine runs during the activation of the "start-by-pass" circuit, but does not run in the normal mode.


As noted.... check coil voltage with the key switch in the "run" mode.
If you see no voltage, then it may be possible that the normal ignition circuit has a fault of some sort.





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