1986 3.0 mercruiser won't start please help

johnnybyankee · May 11, 2009

hello all i am working on a 1986/87 mercruiser 3.0 inboard that has a gremlin somewhere i have replaced the points with a pertronix electronic unit as well as the coil no spark from the coil to the distributor so i then took pertronix back out bought new points and condensor set as well as cap and rotor and still no spark from the coil which is brand new could i have a bad ground maybe or fuseible link bad maybe everything works as it should i.e gauges tilt trim shift interruptor etc i am lost can someone please help i tried even bypassing the harness and putting 12 volt straight ot coil and still nothing no spark any ideas fellas ? thanks john

rocket350 · May 11, 2009

Re: 1986 3.0 mercruiser won't start please help

Make sure your getting 9 - 12 volts at the + side of the coil with a multimeter, and make sure your points are installed correctly meaning the wire that screws on the points are not touching and grounding out anywhere around the base. The wire needs to be secured to the points ONLY.

Bt Doctur · May 11, 2009

Re: 1986 3.0 mercruiser won't start please help

To do that correctly you need to remove the wires off the + side of the coil.
If there is still no spark ,remove the grey wire(tach feed) from the neg side of the coil.
Still nothing sends us to the points, are they gapped properly .018-.020 (a matchbook)on the high side.Are they grounding out? Are they opening? is the black wire good (not grounding out or broken internally?) do you get a meter reading (ohm`s)when you connect to the black wire and ground the points?

rocket350 · May 11, 2009

Re: 1986 3.0 mercruiser won't start please help

Oh yeah, check your shift interupt switch too.

johnnybyankee · May 11, 2009

Re: 1986 3.0 mercruiser won't start please help

shift interupt is working properly when testing at the coil i need to dissconnect the purple lines from the coil is this correct? and then test the coil itself? coil should read 12 v correct? i have checked the points and they are gapped correctly at .0019 i replaced the black lead coming from the points thinking possibly it was grounding out still nothing

Bondo · May 11, 2009

Re: 1986 3.0 mercruiser won't start please help

coil should read 12 v correct?

Ayuh,... Does it,..?? At the (+) terminal,..??

johnnybyankee · May 11, 2009

Re: 1986 3.0 mercruiser won't start please help

ok fellas i found the problem i removed the grey tach wire and it fired right up what is reason for this though? bad tach ground or just junk tach ? thanks for all the help guys

Don S · May 11, 2009

Re: 1986 3.0 mercruiser won't start please help

Bad tach. It IS the ground. and shouldn't be

johnnybyankee · May 11, 2009

Re: 1986 3.0 mercruiser won't start please help

ok thanks again i'm going to order a new one tonite you guys are a big help one other question i have a purple wire with white dashes coming off the starter going to the coil what is the purpose for this wire it has pwr with the key on and while cranking the stud has broken off the starter solenoid boat stil starts though? any thoughts? thanks again all john

Don S · May 11, 2009

Re: 1986 3.0 mercruiser won't start please help

It puts full battery power to the coil for starting only.

JustJason · May 11, 2009

Re: 1986 3.0 mercruiser won't start please help

When you crank the engine there is a normal voltage drop that happens in the engines entire electrical system. The coil needs a minimum amount of voltage to fire. That wire provides a more direct path to the battery and is less susceptible to the drop.

1986 3.0 mercruiser won't start please help

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