5.7 coil issues

[Smitty302]

i put a 94 mercruiser 5.7 with a thunderbolt 4 ignition in my 96 crownline that had a thunderbolt 5 ignition and i keep burning coils, i replaced both coil and sensor in the distributor, runs great for awhile then just quits, is it something to do with putting the thunderbolt 4 in when the boat was a 5 or could it be a ground issue? Thanks in advance, also was told it could possibly be the alternator?

 

[southkogs]

Welcome aboard: I moved your thread into the Mercruiser forum. You should get a few more views this way.

 

[Scott Danforth]

Boat doesn't care what ignition system the motor has

However the coil must match what the ignition system needs

 

[Smitty302]

Boat doesn't care what ignition system the motor has

However the coil must match what the ignition system needs

Ok that’s what I was told, and the distributor and everything was what was original to the 94 so then that should check out. I’ve checked the ground a few times and cleaned them too, may check them again though, thanks, not sure where else to look.

 

[Bondo]

and i keep burning coils,

Ayuh,...... Welcome Aboard,..... Please explain,..??......

 

[Smitty302]

Ayuh,...... Welcome Aboard,..... Please explain,..??......

I’ve put boat on the water 3 times, all three times it has died, first time it lost spark and I replaced just the coil. It happened again the next time, died, no spark. I replaced the coil and the pickup sensor, genuine mercruiser parts, boat ran great, went for a few hour ride, thought that had fixed the problem. Took it out again and was on the water maybe 10 minutes and died again, no spark. I haven’t changed the coil again yet, but I’m sure that’s what it is, I have checked and cleaned the grounds, it has been tuned up, new plugs, wires, distributor cap and rotor. Just trying to figure out what to do.

 

[04fxdwgi25]

Have you checked the ignition cut out switch on the shift linkage?

 

[Fun Times]

Have you tried using both a new and old original high tension coil wire with good rubber end boots, so they don’t leak spark? A bad coil wire will cause these types of issues.

Also check the temperature of the coil.

Check the voltage at the coil and alternator to compare notes.

Run the engine at dark looking for spark leakages (a light show) everywhere.

Tachometer gauge working normal?

Have you checked the ignition cut out switch on the shift linkage?

, That seemed to be this one's issue, https://forums.iboats.com/threads/mercruiser-4-3-keeps-burning-ignition-coil.752262/

 

[Scott06]

Are you getting the correct coil -internal vs external resistor ?

Had a similar issue on a can years back - would intermittently loose spark, and was destroying ignition components like cap rotor looked like arc welding was going on inside. Replaced the coil, couple month later coil was bad. Finally found a really good mechanic who could help- he said the sensor in dist or module was bad. Apparently could trickle voltage to coil when ignition was off heating up coil. In this case the senor was not available separate from dist, so got a dist for the sensor and ignition module from a junk yard and that fixed it .

 

[Smitty302]

Have you checked the ignition cut out switch on the shift linkage?

No I haven’t, I’ll look into that

 

[Smitty302]

Have you tried using both a new and old original high tension coil wire with good rubber end boots, so they don’t leak spark? A bad coil wire will cause these types of issues.

Also check the temperature of the coil.

Check the voltage at the coil and alternator to compare notes.

Run the engine at dark looking for spark leakages (a light show) everywhere.

Tachometer gauge working normal?

, That seemed to be this one's issue, https://forums.iboats.com/threads/mercruiser-4-3-keeps-burning-ignition-coil.752262/

I will try this as well

 

[Smitty302]

Are you getting the correct coil -internal vs external resistor ?

Had a similar issue on a can years back - would intermittently loose spark, and was destroying ignition components like cap rotor looked like arc welding was going on inside. Replaced the coil, couple month later coil was bad. Finally found a really good mechanic who could help- he said the sensor in dist or module was bad. Apparently could trickle voltage to coil when ignition was off heating up coil. In this case the senor was not available separate from dist, so got a dist for the sensor and ignition module from a junk yard and that fixed it. As far as I know it’s the correct coil, bought it from local marine, best in the area, took vin to him and made sure all was right, if I can’t get it figured out, this is where I’ll be taking it. Hoping I can get it figured out though.

 

[Smitty302]

Have you checked the ignition cut out switch on the shift linkage?

How do you check this?

 

[04fxdwgi25]

How do you check this?

I would get a good service manual, probably the Mercruiser ones for the engine and Alpha drive unit.

Short check. On stbd side exhaust riser is a "shift plate" where the shift cable(s) merge. One is from the console shifter and the other goes down to the drive. There is also a micro switch with 2 wires on it on the plate.

These cables need to be adjusted quite precisely for all to work. That switch cuts out the ignition while shifting the Alpha drive while in the water and preloading the drive dogs in the lower drive unit by water pressure on the turning props.. (it's not need when on the trailer, as the prop is not preloaded by water). Without that switch, the Alphas are very difficult to shift in and out of gear.

If the lower cable going to the drive unit is bad, or the cables are adjusted wrong, it will mess up all that timing and make the switch kill the ignition. A bad switch will kill it too.
To test if switch is killing the engine, disconnect one wire from the switch