Mercruiser 525 Experts: HELP
 

I bought a brand new Challenger mid cabin boat with a 525 EFI engine. The boat has 15 dealer demo hours on it which mainly was the owner using at the LOTO.

While the dealer was servicing it and getting it ready they discovered the engine won't shut off now all of a sudden. They have tried a new engine computer and all new engine wiring harness. Plus I know they have replaced some relays. I sure miss my old Baja with carbed 500's.

Anybody got any ideas how to shut off a 525 that is still under warranty. My 10 day vacation to LOTO looks like it is going to boatless. Sounds like the dealer is giving up and waiting on Mercury Racing to send a technician. Holy crap I wouldn't think it would be that hard to turn off a 525 engine

Well it certainly sounds like a relay is sticking or there is a problem at the key switch. Should be able to check if the key is actually turning the on/off signal to the fusable link. From that point, I would be thinking relays. Is it 2 motors, or just 1? If 2, are they both doing the same thing? When turning key off, it should flip the ignition relay.

Dustin

Sound's like it is time to find another shop to work on your boat !!!!!!!!!!!!!!!!!! :mad:

Boy I miss carbs, distributors and non-EFI systems sometimes. You could run down the entire ignition wiring diagram in your head in 30 seconds and solve a problem like this in another 30 seconds.

The key switch checks out ok. It's just a single motor. It seems to me a relay is about all that's left, other than the boat wiring from the key to the harness connection. Hard to believe the boat wiring could just go bad after just 15 hours.

You will probably find, if you find it, that there is a screw somewhere along the harness that is shorting the key on power wire and another 12V source together. On a car the screw would short to ground and blow a fuse, but on a boat it will simply make the connection. Typically you will find this from a speaker or accessory installation near the Merc wiring harness. On a single engine boat like that it should not be that hard to trace the wire. Worse comes to worse, if the "key on" power wire is always on at the engine end, cut it and run a new wire from the key switch to the engine end, you can always resplice the original wire back if you find the short.

I talked to the mechanic working on the boat this am. ECM, relays, wiring harness are all new from Mercury racing. They hooked the engine up to their test stand and their electrical harness and the engine still won't shut off.

I could certainly agree with this. This would be my next test, manually run the wires from the key to the harness. I think the problem is semi-simple, the ignition relay is what is powered on/off by the key switch, starter solenoid and breaker. Something in that loop is not cutting power when key off. If you pull the ignition relay when running, motor should die. I would assume they changed this relay first. If you did, then that means this relay is being powered, so then just follow the wires back from here.