Mercruiser 4.3 keeps burning ignition coil

[mguardado7293]

Hello every one, I have a 1993 mercruiser alpha 4.3l v6 on a 93 sea ray
Last week my starter went out & I replaced it right away. But now when I got back in the water I started the engine and it started perfectly fine
30 min later I shut it off & it wouldn’t start anymore (only crank, no spark)

I determined I had a faulty ignition coil & I had a spare one in my garage from another boat (I also ordered a new one) .
when I swapped out ignition coil the engine fired right up, but after 15 min of running I shut the motor off and went back to start it and it wouldn’t run(only crank, no spark).
By then I had my new ignition coil in and I replaced it for a 3rd time.
once again engine fired right up and after about 5min of running, it shut off when I was going to switch from neutral to drive and it wouldn’t start again (cranks, but not spark).
I’m assuming the 3rd ignition coil is gone aswell.

has anyone seen this before?
Could me replacing my starter cause this?

 

[achris]

...
Could me replacing my starter cause this?

Not unless you shorted some wiring, no.

 

[Grub54891]

your lower shift cable is either wore out, or mis-adjusted. It's sticking in the kill the ignition mode.

 

[achris]

your lower shift cable is either wore out, or mis-adjusted. It's sticking in the kill the ignition mode.

With a points system I'd agree, but this is a Thunderbolt system, all the shift cutout switch stops is pulses to the module, it doesn't ground the coil.

 

[Scott06]

Hello every one, I have a 1993 mercruiser alpha 4.3l v6 on a 93 sea ray
Last week my starter went out & I replaced it right away. But now when I got back in the water I started the engine and it started perfectly fine
30 min later I shut it off & it wouldn’t start anymore (only crank, no spark)

I determined I had a faulty ignition coil & I had a spare one in my garage from another boat (I also ordered a new one) .
when I swapped out ignition coil the engine fired right up, but after 15 min of running I shut the motor off and went back to start it and it wouldn’t run(only crank, no spark).
By then I had my new ignition coil in and I replaced it for a 3rd time.
once again engine fired right up and after about 5min of running, it shut off when I was going to switch from neutral to drive and it wouldn’t start again (cranks, but not spark).
I’m assuming the 3rd ignition coil is gone aswell.

has anyone seen this before?
Could me replacing my starter cause this?

I don't know how you would test this but you may want to try replacing the sensor in the distributor. I had a similar situation on a VW where sensor in distributor failed and would trickle voltage through it to coil. Kept ruining coils, replaced distributor and thus sensor problem went away.

 

[mguardado7293]

This weekend I will check voltage at the coil terminals to see if the voltage drops when the engine is running.

also The distributor/plugs/cables are all new, 6-7 months old about 10 hours of use on those

 

[Grub54891]

With a points system I'd agree, but this is a Thunderbolt system, all the shift cutout switch stops is pulses to the module, it doesn't ground the coil.

Well true, but it still cut's out the spark momentarily so it'll come out of gear?

 

[achris]

Well true, but it still cut's out the spark momentarily so it'll come out of gear?

Yes, but even shorting the interrupt switch and leaving the key ON won't kill a coil.

 

[nola mike]

Yes, but even shorting the interrupt switch and leaving the key ON won't kill a coil.

I think he's saying the coil isn't actually dead, it's the switch cutting spark. I'm curious if the OP tried swapping one of the "bad" coils back in

 

[mguardado7293]

I think he's saying the coil isn't actually dead, it's the switch cutting spark. I'm curious if the OP tried swapping one of the "bad" coils back

Yes, but even shorting the interrupt switch and leaving the key ON won't kill a coil.

This weekend I will check voltage at the coil terminals to see if the voltage drops when the engine is running.

also The distributor/plugs/cables are all new, 6-7 months old about 10 hours of use on those

I put in a new coil this weekend & fired right up

Voltage at the + wire is 10.9 while running

not

 

[mguardado7293]

I think he's saying the coil isn't actually dead, it's the switch cutting spark. I'm curious if the OP tried swapping one of the "bad" coils back in

I just put original coil back in & fires right up!!

coils aren’t burning, but somehow it only resets once I disconnect power from switch

 

[Scott06]

I would try the following when it happens-

measure for 12v at Positive side of coil- you may have loose or corroded wiring if only getting 10.9 volts - check the cannon plug between engine and boat harness. somewhere you are loosing volts. Basically the ignition system gets power to the dash from the engine 12v positive supply to starter - goes through the 50 a breaker, cannon plug up to the dash... through ignition switch, kill switch etc ultimately ending at purple wire that supplies choke and ignition system- a bunch of connections that can be loose or corroded.

follow the thunderbolt troubleshooting guide https://bpi.ebasicpower.com/faq/MERCSB92-11.htm the older ignition sensors in dist were not sealed if you have the stud connectors I would replace it regardless of working.

I would disconnect the shift interrupt to rule that out. I think but not 100% sure that disconnecting should effectively bypass this.

 

[mguardado7293]

I would try the following when it happens-

measure for 12v at Positive side of coil- you may have loose or corroded wiring if only getting 10.9 volts - check the cannon plug between engine and boat harness. somewhere you are loosing volts. Basically the ignition system gets power to the dash from the engine 12v positive supply to starter - goes through the 50 a breaker, cannon plug up to the dash... through ignition switch, kill switch etc ultimately ending at purple wire that supplies choke and ignition system- a bunch of connections that can be loose or corroded.

follow the thunderbolt troubleshooting guide https://bpi.ebasicpower.com/faq/MERCSB92-11.htm the older ignition sensors in dist were not sealed if you have the stud connectors I would replace it regardless of working.

I would disconnect the shift interrupt to rule that out. I think but not 100% sure that disconnecting should effectively bypass this.

I get 12.3 volts with ignition on

10.9 once running

Also figured out I wasn’t burning the coils, lower shift cable gets stuck when I go from Forward to neutral therefore killing the spark
Once I manually tap the cable it moves to position allowing me to get spark once again (this would happen when I move the cable to the side to replace coil)

 

[Scott06]

I get 12.3 volts with ignition on

10.9 once running

Also figured out I wasn’t burning the coils, lower shift cable gets stuck when I go from Forward to neutral therefore killing the spark
Once I manually tap the cable it moves to position allowing me to get spark once again (this would happen when I move the cable to the side to replace coil)

Ok then likely you need to replace lower shift cable.

I don't think the 11 volts running is right you are loosing voltage somewhere, would think at some point this may become an issue

 

[nola mike]

Ok then likely you need to replace lower shift cable.

I don't think the 11 volts running is right you are loosing voltage somewhere, would think at some point this may become an issue

Agreed. Google "voltage drop test" for how to troubleshoot the issue. Looks like @Grub54891 Nailed the original problem...