1996 2t2 115 elpto merc upper rpm problem

[greghost]

Ok here we go. I bought a 1996 115 2+2 merc serial # is OG 466864.Motor runs fine up to about 3000 rpm but then it starts knocking like its pre detonating kinda like a car that has the timing too far advanced.In my manual it shows switch boxes but this motor has cdm's .When did mercury make the switch to cdms?It has a rev limiter which when kicked in advances the timing to 30 degrees per my 100$ manual..Im thinking this may be the problem.How do I properly by pass it?I was told to just unplug the purple wire coming out of it but I
m leery on doing anything until I can get some more info.Any help would be appreciated.

 

[flyingscott]

CDM modules came out after 96. Maybe you have a replacement powerhead or someone upgraded the ignition. I believe 99 was the first year for the CDM modules.

 

[racerone]

The knocking is a red flag.----I suggest you do a compression test.-----Post the actual values here.-----I doubt a rev limiter advances ignition on outboard motors !

 

[greghost]

The knocking is a red flag.----I suggest you do a compression test.-----Post the actual values here.-----I doubt a rev limiter advances ignition on outboard motors !

compression is 135 on all four cylinders

 

[greghost]

CDM modules came out after 96. Maybe you have a replacement powerhead or someone upgraded the ignition. I believe 99 was the first year for the CDM modules.

serial # on freeze plug is the same as the sticker on clamp from what I can tell any serial # above 438--- has cdms on it according to merc manual

 

[faztbullet]

A rev limiter does not control timing...it only shorts ignition to ground causing a stutter

 

[faztbullet]

From the real manual...(90-830234R3)

 

[greghost]

Thanks for the reply