Twin Mercruiser 30s one engine eats ignition modules for lunch

"Hi All,

I'm new here a

"Hi All,

I'm new here and seen quite a bit of info that is quite good, I'm hoping that someone has some suggestions for my issue.

I have a Bertram 25 with twin mercruiser 3.0LX motors, one is an 86 and the other is an 07. My issue is with the 07 motor.

This started last year when after a 2hr run to the fishing grounds the engine died and started back up again instantly. The engine would run for about 1/2 hr and then all of the sudden die instantly, always restarting after a few minutes. The issue progressed to a point where sometimes the engine would start and sometimes it wouldn't, every time it wouldn't start because of no spark.

I replaced the plugs, wires, cap, rotor, then coil, and finally the ignition module and got a few runs in to save the season.

This spring, the engine wouldn't start and following advice I found here I swapped the wire with the diode that connects the coil to the distributor and got the engine running.

I noticed that when the engine got hot, the tach would start bouncing and if I went over 3000rpm I would hear electrical discharge and the engine running rough. It got to the point where I ordered another ignition module.

The new ignition module lasted 4 trips before the tach started bouncing and I'm back in the same place. Last trip out I was coming home and The tach started bouncing so I took some ice from the cooler and held it on the bottom of the distributor and cooled down the ignition module and it got the engine running properly. A few minutes later when hot again the engine was running rough and the tach bouncing.

I've had 2 different mechanics look at the engine and neither have a clue.

I'm thinking of constructing a custom heat sink and attatching it to the bottom of the distributor to dissapate the heat or potentially getting a lower temp thermostat.

Anyone have some suggestions?"

A sick Tacho can cause problem

A sick Tacho can cause problems with the ignition system. Disconnect the Taco from the coil and see how it goes. At least that will isolate one item that can cause problems.

"Matthew:

The tach is my th

"Matthew:

The tach is my thought too. Does your engine compartment use plastic air ducts from the side of the boat? If it does, some of the air diverters have an air inlet closed off. If you find it that way you can open it and duct fresh air to the dist. area."

Does anyone know if heat trans

Does anyone know if heat transfer grease is supposed to be used when changing out modules?

"The taco circuit often gets o

"The taco circuit often gets over looked. Especially the wiring from the engine compartment to the dash, and the wiring at the dash often looks like a rats nest. Short behind the dash on the taco circuit will kill the ignition. A failure of the electronics inside the Taco (leaky coupling capacitor on the signal input)as the taco heats up will cause all sorts of intermittent problems.
Seems as though all the other components in the ignition system have been replaced with new.
If it was over heating in the engine compartment, I would have thought that would have been a problem right from when the boat was new."

"My boat is a 1964....... It

"My boat is a 1964....... It is probably on its 2nd or 3rd set of motors by now.

I replaced all of the wiring and guages when the port motor was replaced, I got 1.5 seasons of flawless performace before my troubles started.

Maybe the tach is bad, I have my old ones so I will swap it out to try. Is there any diagnostic test one can do?

The tough part here is that I typically run 2 hrs out troll for 8hrs and come home, I can't make my trips If I can't count on both engines. I can cruise at 24kts with both motors but only 5kts on one, no fun if your 40+ miles offshore and want to come home."

"I used the heat transfer grea

"I used the heat transfer grease which came with the replacement modules.

As for heat, there are vents and it doesn't seem to get too hot in the engine compartment"

"The engine with the trouble s

"The engine with the trouble seems to run at 150 degrees and sometimes floats to 160 when trolling, at cruising speeds seems to be rock steady at 150.

My other engine runs pretty consistent at 140.

I am considering changing the thermostat for this reason."

"The temps are in the ball par

"The temps are in the ball park, so I wouldn't bother changing the thermostat.
Never seen gauges that accurate, they are only indicators !"

matthew krause
It may give yo

matthew krause
It may give you an indication of your problem if you took a voltage reading on the sicko engine to see if it is fluctuating.
Nert

"Bert, What is your theory?

"Bert, What is your theory?

I now carry a multi-meter on every trip so electrical tests are no problems....

My volt meters tend to stay right at 14.75v (unfconfirmed w/multi-meter)as I have a few accessories always on like radar, Fishfinder, GPS, dual VHFs. Both engines have an extra battery cable which is tied in at the starter lug which then goes to a battery isolator and then to my house batteries. I have confirmed that I consistently get 13.8v at my house batteries and they stay well charged."

matthew krause
I was just thi

matthew krause
I was just thinking that if the voltage was spiking or you were getting a low voltage at times it may be causing your problem.
Bert

I swapped out the tach on the

I swapped out the tach on the engine with issues with an old tach that came with the boat. We took the boat out today and had the boat ran flawless for 30min at 3000rpm straight into legit 2-3' seas. I then turned onto a beam sea and cranked it up to 3400-3500rpm and within 2-3 min the tach started bouncing from the 3400 to 6000rpm. I did not hear the strange noises that I had heard before. I slowed down and opened up the engine compartment and then brought the rpms back up and both engines seemed to be running the same rpm yet the port engine tach was all over the place.

I checked the voltage coming out of the alternator and had a rock solid 14.6v and then checked the voltage at the purple lead off the ignition switch and saw the same 14.6v

Curiosity here...... The sender wire for the tachometer is grey and I don't see any grey wires anywhere near the coil or ignition module.