Merc 3.0 Ignition fuse blowing

[Tayler]

I have a 3.0 Mercruiser on a 1996 192 RS Stingray. A couple of weeks ago we were out and every time I punched the throttle forward I noticed a small ?bog? or loss of power. The engine seemed to step up and run fine after the slight hesitation. A week later we were out and we got under way. The same thing happened but the boat ran fine. We stopped for awhile and started it back up, got going and then the engine lost electrical power.

I snooped around and saw that the ignition fuse had blown. I rooted around and wiggled the wires @ the ignition fuse, replace the connection @ the battery terminal for the power supply to the GPS (totally independent from the ignition circuit) because I saw corrosion. I replaced the 10 amp ignition fuse and started her up again. Punched the throttle and the thing bogged and after about 100 feet the fuse popped again.

After a long tow home and vicious sunburn I got into the wiring and started to clean house.
-Replaced ignition switch ? Broken terminal
-Cleaned all grounds on engine block and @ battery ? corrosion
-Replaced fuse bus and ground block attached to the bus ? corrosion

The engine ran fine at idle in the driveway. I thought that I had the gremlin out of the boat. We got it out on the water and ran it for about 20 minutes WOT and got to the ramp picked up some passengers and 100 feet after we left the fuse popped again. Same issue under the same circumstances. Engine gets warmed up then it falters and blows the fuse.

After doing some research I have found a common issue with owners of boats with this motor and its ignition fuse popping. Nobody has seemed to find a particular cure or fix for this.

There are a lot of suggestions as to its cause.
The purple wire coming from the ignition switch having to much draw.
I.e. gauges, accessories or powering engine components.

The starter - breaker installed - kept fuse from blowing a few times but it still stalls out and it eventually exploded the fuse and melted the terminal.

Distibutor - How do you diagnose this?

Starter slave solenoid - How do you diagnose this?

Choke - ?

The Alternator - Battery stays charged and all components work fine. But could this be the problem when the engine is @ higher RPM?

Hydraulic trim pump - disconnected trim pump - still blows

Trim sender - disconnected trim limit switch - still blows

Shift interupter switch - ?

Seems to idle fine and only blows when the engine is under a load. After the engine has run for awhile and warms up, higher RPM?s start the issue. After that the fuse just keeps popping until you let is sit for awhile. I am tempted to rip every wire off the boat and start over @ this point. Sombody stop me.....

Thanks in advance

Tayler

 

[Don S]

Re: Merc 3.0 Ignition fuse blowing

Which wire is this 10A fuse in? The red/purple wire, or the purple wire? If it's in the red/purple wire to the I terminal on the ignition switch, it's supposed to be a 20A fuse.

 

[Tayler]

Re: Merc 3.0 Ignition fuse blowing

I notcied this in the schematic. However the stock fuse bus has an ignition terminal labled and has a 10 listed for that terminal. I blew about 5 or 6 fuses and eventually put in a 25 amp fuse that blew too. Out of shear desperation I built a bridge wire. The engine would turn but not start. Seems like something gets over heated and causes a short.

 

[Don S]

Re: Merc 3.0 Ignition fuse blowing

You mentioned you disconnected the trimp pump, not sure where, but assuming you have the trim and tilt buttons in your control, try disconnecting the plug with the 3 wires from the trim pump and see if it does it.
From your discription, you may have some bare wires shorting inside the control handle whenever you give it throttle.

 

[Tayler]

Re: Merc 3.0 Ignition fuse blowing

I wish I could get my hands on the idiot who ran the wiring to the alternator. I was on the battery side of the motor. I was checking the brown wires going to the bildge pump and could not get a good view. I went to the port side and it was only when I put my head down on the deck that I saw a metal clamp about 10 inches away from the rear side of the alternator. I saw the edge had some white corrosion on it and just started laughing. Peeled the metal clamp back and viola there was the red, yellow and purple wires touching bare metal and had almost worn through all three wires. Only the purple wire was exposed to the metal. These metal clamps are supposed to have been installed with the plastic conduit guarding the wires from it. The dope that installed it cut the conduit about 3 inches to short and created a 300 dollar / 8 hour / 3 tow nightmare because they were to damn lazy to cut another piece of plastic conduit and then clamp the damn thing down.

 

[Don S]

Re: Merc 3.0 Ignition fuse blowing

I would guess about a quarter of my jobs are fixing problems that "Previous Owners" intall into their boats.