Logo
FULL SITE MENU

1986 Mercruiser 305 5.0L

M

muddy

New member
hello i am keen to get this Bertram back on the water so any help would be awesome (1986 305 mercruiser carby 5.0L)
Have a no spark issue with this Mercruiser
i just put new heads and manifolds risers on and it, has not been started for months, now no spark at the spark plugs,
i have 0 to 5 volts pulsating at the white wire with a green trace terminal at the distributor ignition sensor,
and twelve volts at the white wire with a red trace at the distributor ignition sensor
is this normal i have done the remove white wire with the green trace with ignition on from the distributor sensor and i got the coil to spark when grounding this wire quickly striking reading previous forum`s said thats a fault with the distributor sensor, but i would like to be 100 percent sure before ordering one
 
when i take a wire and run it from the battery to the coil positive side,
i get a good spark at the coil, thats with a spark test plugged in to it
but still only get one spark while cranking at the spark plugs after still bout 8 , 360 % turns of the crank shaft
is like there is voltage been taken away from the ignition system when cranking
i have two battery `s on the starter in parallel so have plenty of volts and amp`s
i took out the distributor out from the engine block and spun the rotor button around clock wise with my fingers,
this actived my coil lead spark test every time with out fail
now going out to see if it will activate at the spark plugs,
either a voltage loss through the starter motor or ? some one want to help me out please
 
If you have no voltage to the coil + with the key at the ON position. The most likely issue is the shift interuptor switch is shorting the coil to ground as it should ONLY when shifting out of gear when in the water.

Look for the microswitch on the shift cable bracket where the short shift cable and the control shift cable meet at the motor.

There is a small termianl block, one side of the block is ground the other is the wire going to the - side of the coil. Make sure the roller of the switch is in the V notch and not activated. If it is activated this is your issue. If it is not, disconnect the wire going to the coil and see if you have spark?

Start with this and repost......
 
thank`s kghost !
yes there is a shift interrupter switch on the gear shift cables,
with a micro switch that bolts in the cable gear shift cable bracket to the starbon riser,
when manually pushed up and down,
in and out of the v on the roller
it cause`s a spark at the coil lead with the spark plug tester plugged into the coil lead disconnected of the distributor cap,
will have really close look at that terminal block first thing in the morning,
it does show 12 v` at the coil positive purple ignition wire with the key on with a digital meter but will barely light up a 12v test light
also my starter motor may have got some kero & water in the solenoid from when i honed out the cylinder`s! before i put the new heads on,as the block was still in the boat when i did the job, i covered the starter motor with plastic but this may not have been enough
as it is pulling far to much voltage and with two battery`s in parallel even jumped started with a car with 40 amp alternator with the engine running, it dropped to 9 and 8 volts at the coil + purple ignition wire terminal, after bout the third rotation of the crank shaft the starter motor starts to labour`s a little more than it should,
so i have taken that off and see if`s it`s worth servicing
or i will just fit a new one, would appear watching the spark at the tester plugged in to the coli lead and the volt meter at the same time,
that the igniton system spark weakens when the voltage drop`s 9 volts and stop`s all together at 8 volts
thank`s i let you no how` it goes tomorrow
 
The interruptor switch designed to KILL the ignition when shifting OUT of gear when in the water. It shorts the - side of the coil to ground. It does not generate a signal for spark!!!!!

When in a "neutral" state, at rest in the V notch. It does nothing to the ignition circut Unless it is internally shorted.
 
thank`s kghost, i orded in a new starter motor, (2 week`s later) the new starter motor was much smaller in size and had 13 teeth pinion gear instead of 9 teeth, so i fitted that and cleaned all earth connection`s,( the new starter motor was a lot more quite and provided more torque, was in-pressed for the size of it ) jump started the engine from a car to the Bertram`s main battery , and the engine started straight away, but stop after a few second`s, i did remember that there was a lot of oil in the cylinder`s from after the hone job i did, i removed the spark plug`s out and they where covered in oil, so i squirted de wax highly flammable solvent that panel beater`s use to remove oil from body panel`s before spray painting into to each plug hole refitted the spark plug`s and started the engine again, ran fine after that with a few pump`s from the throttle lever!!! so it was a corroded starter motor that was causing a voltage drop to the ignition system, and a oil in the cylinder`s was not helping either with the weak spark that i was was getting to the plug`s!!! thank`s for the imfo on the gear shift safety switch, some thing to watch out for in the future! cheer`s!! :)
 
Last edited:
Back
Top