blowing fuse at start

[scottberry]

The other day the boat wouldn't start. I finally traced it down to the 15 amp fuse in the ecm box on top of the motor (5.7 mercruiser). There are three fuses in the lid of the box that have two 15 and one 10 amp fuse. This fuse seems to power the fuel pump and the audible alarms. I replaced the fuse and everything was fine for a day. The next time out the boat started at the ramp and ran fine for an hour or so. When I tried to start it after some skiing, it toasted another fuse. I replaced it and it worked fine for the rest of the day.
Today I was trying to troubleshoot the issue. Now everytime I turn the ignition to the first position, the fuse blows. I traced the two wires from that fuse and they go to a pink with red stripe and red wire. the red goes to the coil and the pink branches out to the water temp and drive level sensors and then goes to a module called ECU that is inside the black box.

Any thoughts on what is tripping this fuse?

 

[scottberry]

Re: blowing fuse at start

clarification. The pink and black wire splits off to the drive sensor, water temp sensor, the BTCU and the ECM.

Any help would be appreciated.

 

[Don S]

Re: blowing fuse at start

Not every Mercruiser engine and EFI systems is the same.
Got a MCM Serial Number handy?

 

[JustJason]

Re: blowing fuse at start

If your poping fuses i'd start by checking your battery connections and making sure they are good, clean, and tight. Are you using wingnuts or stainless steel nylon lock nuts?

 

[scottberry]

Re: blowing fuse at start

I checked and cleaned all of the battery connections and they do have the stainless wing nuts.

I tried disconnecting everything one at a time that is connected to that circuit (drive sensor, water temp sensor, oil pressure sensor, fuel pump) and it still blows a fuse.

I by passed the fuse with a jumper wire and it blew the main breaker at the ecm box.

I reset it to keep testing and nothing yet.

The only thing that I have had changed this year was the starter. I took on some water last year and the starter was under water. I had intermittent starting issues the rest of the year so I replaced the starter with a high torque unt at the fisrt of the season. Been out several times and itr was fine. The fuse just blew the other day. Now it is everytime I turn the ignition to the first postion. No fuel pump and no audible alarm.

 

[rbh]

Re: blowing fuse at start

hey there-
it almost sounds like you have a dead short, unplug all the connections and do a ohms resistance test on all the leads untill you find the one that has high resistance.
I would start in the bilge area were you had water problem previously.

rob

 

[JustJason]

Re: blowing fuse at start

and toss the wing nuts... you need s. steel nylocks...

 

[Fun Times]

Re: blowing fuse at start

The other day the boat wouldn't start. I finally traced it down to the 15 amp fuse in the ecm box on top of the motor (5.7 mercruiser). There are three fuses in the lid of the box that have two 15 and one 10 amp fuse. This fuse seems to power the fuel pump and the audible alarms. I replaced the fuse and everything was fine for a day. The next time out the boat started at the ramp and ran fine for an hour or so. When I tried to start it after some skiing, it toasted another fuse. I replaced it and it worked fine for the rest of the day.
Today I was trying to troubleshoot the issue. Now everytime I turn the ignition to the first position, the fuse blows. I traced the two wires from that fuse and they go to a pink with red stripe and red wire. the red goes to the coil and the pink branches out to the water temp and drive level sensors and then goes to a module called ECU that is inside the black box.

Any thoughts on what is tripping this fuse?

Are you the original boat owener? It kind of sounds like you moved some wires around and made the short wores.

 

[scottberry]

Re: blowing fuse at start

The engine was changed last year but it has been running fine. This just started the other day.

So, am I looking for a wire that is touching ground or one that is missing ground?

 

[Fun Times]

Re: blowing fuse at start

The engine was changed last year but it has been running fine. This just started the other day.

So, am I looking for a wire that is touching ground or one that is missing ground?

It would be more of a wire that might be cutting in to some where in the middle of it, Or the wire harrness going around a sharp turn and cutting into it. Or the part it self could be going bad. Or you have a loose wire some where at the end of it.Here is what the three fues are for, 16- Fuel Pump Relay (15 Amp)
17- Injector Fuse 15 Amp.) ECM, DLC, Battery
18- ECM Fuse (10 Amp.) ECM, Ignition, Injectors, Knock Sensor
Module. You could ohm's check each wire from end to end to see if you get any reading at all or if you get A hi or low reading. you will want a low reading. And at the same time you are reading the wire you will want to wiggle the wires to see if you get a big change in the ohm's reading. Good luck.

 

[Glastron_V210]

Re: blowing fuse at start

1) Seperate the wires feeding from the fuse. You may have multiple shorts.

2) Buy an ohmmeter. Connect 1 end to the - battery post and test each wire for ohms...there will be at least one with low ohms (13.6V/15A fuse = .9 ohms maximum)

3) Trace the wires and find out how they are grounding. It's likely either water ingress to the insulation, or vibration has worn through the insulation or there has been an impact of some type. There is a small chance an electrical device has failed (Ecm, etc..)

4) Connect the non failed wire to the fuse and test. Add wires one at a time after they have been fixed.

Good luck.

Chay