Misfire & Stall at night, after amplifier install.

striker1211

Seaman Apprentice
Joined
Jul 10, 2013
Messages
43
So I have a noodle scratcher here. My 1996 Mercury 115hp 2-Stroke (0G386904) gave me some troubles last weekend. It seems to run fine now. I installed a 360W amplifier and all new speakers in my boat before this last trip. At night time, when the temperature of the air had dropped roughly 10 degree the boat would not start nicely. When it did start it sputtered and sounded almost as if it was doing a no-gas cough. I could hit the throttle in neutral and it would go away for a second but then keep coughing. It stalled out once at idle. I ran the boat around in circles and it seemed to go away for about a half hour. The performance was great while doing circles, got to top RPM/speed fine. While putzing around shore it started coughing again after a few minutes.

The only thing I had changed was the new amp and speakers. I added new power/ground wires and did not use the old wires at all. The fish finder never read less than 12V. It did it when the lights were off but started when the lights were on. I even connected a 12v car jump pack during the spitting/sputter to the terminals and it did not clear up the misfire. Could the amplifier just be a red herring? The half tank of gas before we filled it up that day had been sitting for only 5 days. I use 87 unleaded. One thing to note is that I heard ticking noise through the speakers even with the RCA wires disconnected all day until high RPMs. The clicking/ticking increased with the engine speed. It went away with key off. I think this is due to non-resistor plugs but could it be the alternator/coils? Thanks in advance, once again :)
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,123
Re: Misfire & Stall at night, after amplifier install.

The ign system on that motor is not driven by the battery, so the current drain of the amp should not be an issue. I have never heard of the "electrical noise" of an amp bothering a CDI ignition system. Obviously the test is simple. See how the boat runs with the amp powered down and then turn it on and repeat test.

It is normal to hear the ign sounds thru the amp. OB spark plug wires are solid stainless steel stranded wire, and I doubt that Merc has resistor spark plugs.

On my Johnson, I need to run "Q-supressed" spark plugs (whatever that means) to protect the ign system from spark plug noise. Maybe you have some similar issue?
 

striker1211

Seaman Apprentice
Joined
Jul 10, 2013
Messages
43
Re: Misfire & Stall at night, after amplifier install.

I went out again today during the day. I ran her for about 3 hours and there was not one issue with starting or idling. It started in a half second with a key bump. I swear these boats just like to play with our heads...
 
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