mercruiser 3.7 has no spark

[warthog-puma]

hello. to all. i am new here, but not to boats.

i have a 3.7 liter model 485 that has no spark. i have 12 volts at the coil with the key on and the engine cranking. i have taken the tach wire off at the coil. i have tested the resistor wire and it specs fine.

the ground going to the condenser has been replaced. the condenser reads the specified microfareds (sp?) and the coil ohms out within specs. the points are set and i'm guessing there is more to them than open/close and looking good the high tensoin wires are 1 year old. the cap, rotor, condenser, points are 1 year old. the shift interupt switch in in the neutral position. NO spark.

QUESTION: can the ignition switch still be grounding the coil even though i have 12 volts to the coil while on and cranking? are there other tests for the condenser such as a leak test of some sort? as always the number one quote "it ran great when winterized"
the boat is 30 years old. do I need a REALLY big hammer or a grenade?
any help would be appreciated and thanks in advance

 

[lonemust]

Re: mercruiser 3.7 has no spark

hello. to all. i am new here, but not to boats.

i have a 3.7 liter model 485 that has no spark. i have 12 volts at the coil with the key on and the engine cranking. i have taken the tach wire off at the coil. i have tested the resistor wire and it specs fine.

the ground going to the condenser has been replaced. the condenser reads the specified microfareds (sp?) and the coil ohms out within specs. the points are set and i'm guessing there is more to them than open/close and looking good the high tensoin wires are 1 year old. the cap, rotor, condenser, points are 1 year old. the shift interupt switch in in the neutral position. NO spark.

QUESTION: can the ignition switch still be grounding the coil even though i have 12 volts to the coil while on and cranking? are there other tests for the condenser such as a leak test of some sort? as always the number one quote "it ran great when winterized"
the boat is 30 years old. do I need a REALLY big hammer or a grenade?
any help would be appreciated and thanks in advance

No the ign switch cannot do both groung the system and provide 12volts at the same time to the same wire. It would fry the wire. Pull the coil wire from the cap and hold it a 1/4 to 3/8" away from the block and hit the starter to see if you have spark. If you do get spark replace said wire then pull a plug wire from the spark plug. Use a spark tester or a spare plug(laid against the block) hit the starter again watching for spark. If NO spark then the problem is in the cap. Oh ya first pull the cap, inspect the inside make sure there is no corosion iin it or on the rotor. If there is clean them real good.
When was the last time you changed the spark plugs. You said you changed the wires, cap, rotor, condenser, and points a year ago. but no mentiion of the plugs. If you didnt yet change them out. Old plugs will cause one big headache trying everything else first then finding the problem was the plugs themselves. If you have every ppulled a plug and had spark then put it back in and no start on a lawn mower then you will know what I mean. CHange the plug and it started. Plugs can show good spark out of the engine then put it back in and no spark. I call the senerio flameout. Meaning the plug is not strong enough to spark under pressure in the cylinder. Happens a .lot with cheap plugs. So change plugs FIRST so you know you have brand new ones. If it dont start then do the other stuff.
If it ran before winterization and not now change the plugs first

 

[warthog-puma]

Re: mercruiser 3.7 has no spark

thanks for the reply. i dint think so about the ign switch just had to make sure i was thinking along the right lines. the plugs were changed as well and spark was tested with a spark tester and no spark from the main coil lead or any of the plug wires themselves. the wires are all one year old and the plugs too. does anybody know approx resistance of a main coil lead? i am reading about 16k ohms.. new info.... didnt even think about it. the points were set with feeler gauge and then ran great all last summer. i know you're not supposed to scrape the points with sand paper, does running a feeler gauge through the points essentially have the same effect as sanding them? did i just answer my own question? how expensive are dwell meters, i havent seen one in years. hmmmm

 

[Bondo]

Re: mercruiser 3.7 has no spark

Ayuh,... Change the points, they're glazed over...

 

[warthog-puma]

Re: mercruiser 3.7 has no spark

thanks. will do and report back. and will get a dwell meter if i can find one

 

[lonemust]

Re: mercruiser 3.7 has no spark

I just went though kinda the same thing on mine. When I was checking for spark, I had nice spark at the coil wire but a weak spark at the plug wires. Checked everything; points, condenser, plug and coil wires, cap, and the rotor. Everything checked ok. Let it sit overnite and it started right up ran for 20-30 mins and died would not restart again. Again rechecked everything. Made a new points wire to coil still weak spark at the plugs. Checked coil again it showed bad. Replaced the coil and it started right up and ran for over a hour with no problem. So what I'm saying is to replace the coil and see if that solves your problem.

 

[sgm26]

Re: mercruiser 3.7 has no spark

Unplug the shift interrupt switch in case it is grounding out.

 

[warthog-puma]

Re: mercruiser 3.7 has no spark

it was the points. i checked the shift interrupt switch. put a new set of points on it and dial it in with a dwell meter and fired right up. was going to replace coil and condenser if that didnt work even though they test fine. thanks for the replies.