Mercruiser 140 (1984) - What started as key no longer turning off boat has evolved into boat not starting at all

[Riflejake]

I have a MerCruiser 140. Just got back from the lake, and the key will no longer turn off the ignition. The boat ran fine this morning on muffs in my driveway, but failed to turn off when I remove the key from the ignition 30 minutes later on the lake. Killing the battery to the engine also resulted in no effect, I had to remove the wire going from the ignition coil to the distributor in order to kill the engine. Any thoughts?

 

[brodmann]

Check, clean, and/or reconnect black wire to ignition switch. Once your motor is running, it no longer uses battery power. Sometimes turning choke on will bog the motor down.

 

[Riflejake]

Check, clean, and/or reconnect black wire to ignition switch. Once your motor is running, it no longer uses battery power. Sometimes turning choke on will bog the motor down.

My ignition only has a battery, ignition (accessories) and solenoid

 

[kenny nunez]

On the main starter solenoid there is a small purple/black wire next to the battery cable. Are they touching? If not try disconnecting that wire and check if the engine stops with the key off. If there is no wire like that on the starter solenoid then look at the small boost solenoid for the same color wire. Some alternators have a diode that when it burns out the same condition will occur with the key off.
You did not provide the serial # or year of the boat, that may help.

 

[QBhoy]

Hi. Is it continuing to run, but running very poorly and rough, when this happens ? I’ve seen that happen before when key turned off..keeps running for a while after. This is a result of either timing or fuel issues.

 

[nola mike]

Since we don't know what you're working on, I'm going to say you have a bad TKS diode.

 

[Riflejake]

Check, clean, and/or reconnect black wire to ignition switch. Once your motor is running, it no longer uses battery power. Sometimes turning choke on will bog the motor down.

My ignition only has a battery, ignition (accessories) and solenoid

Since we don't know what you're working on, I'm going to say you have a bad TKS diode.

Mercruiser 140, year is 1984. Running Pertronix 1146A instead of points

When removing the key the engine runs fine indefinitely, have to pull the wire from coil to dist to kill the engine.

I did some wire tracing and believe that the ignition switch is fine. I did fine some curious things though
1. Ignition Coil has continuity from positive terminal to negative with everythingdisconnected
2. There is a faint yellow wire on the positive side of the coil - Testing continuity, I have it from that yellow wire to ground (don’t think it should be grounding)Boat doesn’t run without it

 

[nola mike]

Key off, are you getting 12v at the coil pos when engine off? Presumably you are with the engine on

 

[Riflejake]

Key off, are you getting 12v at the coil pos?

With engine off, no. Haven’t tested with engine on but I’d assume so.

I’ll also add that shutting off my battery while it’s running will not kill the engine.

 

[Riflejake]

Further update: Found the yellow wire on the coil is leading to the choke. No shorts when testing continuity there
Purple leads to solenoid. No shorts.

What’s bizarre is that the engine no longer run unless you hold the key in The start position. Once you let go of the key the engine dies - I did change the ignition switch and have the same results

 

[nola mike]

Further update: Found the yellow wire on the coil is leading to the choke. No shorts when testing continuity there
Purple leads to solenoid. No shorts.

What’s bizarre is that the engine no longer run unless you hold the key in The start position. Once you let go of the key the engine dies - I did change the ignition switch and have the same results

Ok. so not sure how your pertronix is wired. Originally though, when your key is in "start", a purple/yellow wire is energized from the starter, supplying 12v to the coil. When you let off the switch to "run", the ignition circuit takes over. With the points system, the coil is powered by a purple (wonder if this is the "yellow" wire you're looking at) resistance wire from the choke. In the run position it supplies ~9v to the coil. Some of the electronic conversions keep this wire, some use a different coil and replace the resistance wire. At this point it sounds like you have a problem in the ignition circuit. I wonder if you had a short to power somewhere that has burned through your purple wire at some point. Based on your symptoms now, you should no longer have any power to the coil with the key on, and gauges should be dead.

 

[Riflejake]

Ok. so not sure how your pertronix is wired. Originally though, when your key is in "start", a purple/yellow wire is energized from the starter, supplying 12v to the coil. When you let off the switch to "run", the ignition circuit takes over. With the points system, the coil is powered by a purple (wonder if this is the "yellow" wire you're looking at) resistance wire from the choke. In the run position it supplies ~9v to the coil. Some of the electronic conversions keep this wire, some use a different coil and replace the resistance wire. At this point it sounds like you have a problem in the ignition circuit. I wonder if you had a short to power somewhere that has burned through your purple wire at some point. Based on your symptoms now, you should no longer have any power to the coil with the key on, and gauges should be dead.

Hopefully this video makes the explanation easier

 

[Bondo]

Ayuh,..... Welcome Aboard,..... Switch yer meter to dc voltage,.....
Ignition power goes from the key switch to the wire at the choke, to the coil,.....
When starting, ignition power is also supplied by the outside tiny terminal of the starter's solenoid,....
All that appears right,.....

The pertronics trigger I ain't so sure of,.... Donno whether it needs battery power on the red wire, or if it should feed from the coil's (-) terminal to the red wire, 'n block ground on the black wire,....
Never done one,....

 

[nola mike]

Kind of...still hard to tell what's going on. Your P/Grey wire is the P/Y I was talking about. Pertronix wire looks new, and is what's powering the ignition module. Yellow wire...not sure, but guessing that should be hot from the choke with the ignition on (and that terminal at the choke). Usually that wire would be purple, maybe it still is and faded. Continuity tests aren't the correct way to track down your issue. Like I said, sounds like you have a break in your ignition circuit (purple wire, maybe that yellow) somewhere.

 

[nola mike]

Ayuh,..... Welcome Aboard,..... Switch yer meter to dc voltage,.....
Ignition power goes from the key switch to the wire at the choke, to the coil,.....
When starting, ignition power is also supplied by the outside tiny terminal of the starter's solenoid,....
All that appears right,.....

Yup.

The pertronics trigger I ain't so sure of,.... Donno whether it needs battery power on the red wire, or if it should feed from the coil's (-) terminal to the red wire, 'n block ground on the black wire,....
Never done one,....

The conversions need 12v, which is what the red wire should be doing. The black is the trigger wire from the system, so grounds out the coil (-) and should be attached there like a points system.

 

[Riflejake]

Ayuh,..... Welcome Aboard,..... Switch yer meter to dc voltage,.....
Ignition power goes from the key switch to the wire at the choke, to the coil,.....
When starting, ignition power is also supplied by the outside tiny terminal of the starter's solenoid,....
All that appears right,.....

The pertronics trigger I ain't so sure of,.... Donno whether it needs battery power on the red wire, or if it should feed from the coil's (-) terminal to the red wire, 'n block ground on the black wire,....
Never done one,....

Thanks! The meter was at 20V DC.

I have the yellow/red solenoid wire running from the key back to the slave solenoid, to the primary solenoid (tested continuity and good). Purple gray wire comes off solenoid to + on coil (continuity is good). Yellow/Purple wire from the + on coil to carb (continuity is good but the carb clock spring is grounding???)

The Pertronix has been no issue so far. Will try and replace with the spare I have for free (thanks Amazon) and might try a new coil too.

 

[Riflejake]

Kind of...still hard to tell what's going on. Your P/Grey wire is the P/Y I was talking about. Pertronix wire looks new, and is what's powering the ignition module. Yellow wire...not sure, but guessing that should be hot from the choke with the ignition on (and that terminal at the choke). Usually that wire would be purple, maybe it still is and faded. Continuity tests aren't the correct way to track down your issue. Like I said, sounds like you have a break in your ignition circuit (purple wire, maybe that yellow) somewhere.

Kind of...still hard to tell what's going on. Your P/Grey wire is the P/Y I was talking about. Pertronix wire looks new, and is what's powering the ignition module. Yellow wire...not sure, but guessing that should be hot from the choke with the ignition on (and that terminal at the choke). Usually that wire would be purple, maybe it still is and faded. Continuity tests aren't the correct way to track down your issue. Like I said, sounds like you have a break in your ignition circuit (purple wire, maybe that yellow) somewhere.

I’ll try running a jumper

 

[nola mike]

Thanks! The meter was at 20V DC....

(continuity is good but the carb clock spring is grounding???)

You're measuring either volts or continuity, which is it?

The Pertronix has been no issue so far. Will try and replace with the spare I have for free (thanks Amazon) and might try a new coil too.

You can replace it all you want, coil too. Neither are your problem.

 

[Riflejake]

You're measuring either volts or continuity, which is it?


You can replace it all you want, coil too. Neither are your problem.

In the video I was showing continuity, but prior I’ve been testing voltage. Only reason for showing continuity was I thought there’s a short somewhere with the choke.

With key in the run position, not attempting to start, the starter solenoid has 12V from ground to main lug. Purple gray wire next to main lug has .03v from ground to that lug (can’t check for voltage when attempting to start as I don’t have extra hands to start boat), from ground to ignition coil + I have .03v, same as lug on solenoid

 

[Riflejake]

Bit of backstory: on the lake, removing key and the boat no longer turns off. Worked just fine in my drive 30 minutes prior. Killing the battery also didn’t turn it off, so had to remove the wire from the coil to the dist.

Today, start troubleshooting. Engine was running fine this morning, kept trying to find the culprit. For one second, I remove the wire on the positive side of the coil leading to the choke, attempt to start and nothing. I still had the purple wire leading down to the ignition coil and also my Pertronix. Place the carb choke wire back on, boat still won’t start. It acts like it wants to run (sounds like it’s even running), but dies once you release the key from the start position.

I have replaced the ignition switch.
Verified that I have 12Vs to main lug on starter solenoid.

Verified continuity of wire leading from yellow/red at ignition to slave solenoid, verified from slave to master has continuity.

One thing I find odd is that the piece inside of the choke (where the clock spring attaches to and turns) has continuity to ground.

New coil, and new Pertronix will be delivered in the morning