502 MPI Blows 90 Amp Fuse
 

I just put in two 2000 502 MPI in the Pantera to replace the tired 454's.

When I get to approx. 4700 rpm the port motor acts like it wants to shut down.....it doesn't seem like a rev limiter....it's like the key is being turned off.

The 3rd time we hit 4700 all power was lost on the port side. It ended up being the 90 amp fuse attached to the starter.

We rep;aced the fuse and ran it again, it will run all day at 4500. We go up to 4700 and the boat will lurch to starboard when that engine shuts down. It's a momentary shutdown as when the throttles are pulled back a bit, it keeps running.

We kept it below 4700 the rest of the day. Didn't want to test the fuse anymore and go back on one engine again!

The 454's were grounded together with a cable. I haven't attached this cable yet. Hoping it's as simple as that!

Any ideas?

Bruce

Blown fuse
 

It is a little hard to diagnose your problem over the internet but I would like to say something about twin engines. Mercruiser is recommending that, if at all possible, the two engines should be wired separate from each other, separate batteries, everything. Run the boat off of one of the engine/batterys with a battery switch normally open between the two engines. Something to do with voltage spikes (for the computers) I think.
Sincerely
Dennis Moore

I would go ahead and attach the large ground cable between the motors. I can't remember where I read the importance of it but I do know for a fact that the electronics on my boat don't work right without it.

Thanks for the reply Dennis.

I was hoping it would be something easy and obvious. Looks like I'm going to get to know the wiring intimately!

Bruce

blown fuse
 

The only drain on the motor disreguarding a shorted cable that could blow a fuse is the starter solenoid but it is only about 40 amps. I think you need to investigate the altenator. It recharges the batteries thru this fuse and might be exceeding the computer's maxium voltage at high RPM.

On the old engines, the alternater went bad on the port side.

Hmmmm.....interesting.

I have also found the battery caps off on the starboard side. The first time I thought they vibrated off. A few weeks later, they were off again.

Another thing I noticed.......because the port alternater was not charging, I hooked up the battery charger. While checking other things out I heard a hissing noise. The hissing was outgassing from the starboard battery!

Any more thoughts?

Bruce

TT
I will bring an amp meter down this weekend that should tell us something about where the over amping is coming from.

blown fuse
 

You might also check the fuse on the port side. If both key switches were powered by the starbord side the port motor could run off the altenator, but not charge the battery.

This sounds absolutly like what was happening to me back when I brought my boat home new.
Twin 1999 502 mpi's
normal running everything ran great
hard runs sometimes the starboard motor would act like I turned the key off then on right away again.

It took about 3 runs and several trips into the wiring harness.
I knew it had to be eletrical because only electicity can fool you so easily :)

What came out of it was I was finding my battery connections were loose. I removed the wing nuts and literaly tossed them in the river. :)
replaced them with ny-lock nuts and life has been great ever since.:D

Try it you might like it :)

Thanks
 

Thanks MFB.........What the hell, I'll try the stop nuts also.:D

I think the problem lies deeper than that though.

My positve cable for the drive trims are hooked to the starter. Is this normal? Would it be better to have it direct to the battery? Does it matter?

During the year I've had the boat, some of the electrical seems suspect.

FYI
Pantera sold this boat as a bare hull and it was some years later that the boat was rigged by another outfit.. JO and company would have rigged this thing much tighter!

Bruce