mercruiser 350 mag mpi blowing fuse

[ditch-digger]

Need some HELP big time on my boat that is blowing Ecm, injector, ignition and knock module fuse. When I put the boat in the water I can get about 1/2 mile and then this fuse blows. If I immediately replace it and only turn key on, it immediately blows again. If I let the motor rest for approx. 30 minutes, I can get it to hold only If I keep it at idle. If I rev up the motor, the fuse blows and I am back to square one. It seems to me that it is heat related and possibly ignition related, but where and why??? Motor purrs like a kitten when its running(which isn't that long) I would appreciate any help or suggestions. Thx

 

[achris]

Re: mercruiser 350 mag mpi blowing fuse

Hello and welcome to iBoats...

This sounds like a nasty problem... It's going to take time and very methodical troubleshooting to track down...

Here's what I'd do. Replace the fuse with a circuit breaker (cheaper than buying 500 fuses )... Then hook up an ammeter (DMM on the amps scale) and unplug everything that runs off that circuit. Plug each thing back and make note of how much current each item draws... Then take the boat on the water and run it until the breaker pops, then go through the whole process again... I'm sure that something will show as drawing too much.... I know it's very time hunger... but the only other option is to keep replacing things until (if) the problem goes... My way is cheaper, and more satisfying when you nail the sucker. ...

Do you have a wiring diagram?

Chris......

 

[Don S]

Re: mercruiser 350 mag mpi blowing fuse

What's the serial number of your engine?

 

[ditch-digger]

Re: mercruiser 350 mag mpi blowing fuse

What's the serial number of your engine?

Don, thanks for responding. My engine serial # is: OWO369039 Family: 4M9xMO5.7GME D.O.M. 6/2004

Thanks big time for any help!

 

[Don S]

Re: mercruiser 350 mag mpi blowing fuse

Might want to check your serial number, too many numbers.

 

[ditch-digger]

Re: mercruiser 350 mag mpi blowing fuse

Might want to check your serial number, too many numbers.

Im sorry. it is: 0W036039. The other info is correct.

Thanks

 

[Don S]

Re: mercruiser 350 mag mpi blowing fuse

Not much I can do to help you troubleshoot your problem, as Chris points out, it's not going to be easy to locate at all. Have you had it hooked up to a diagnostic computer to see if it shows anything out of the ordinary?

Click Here to download the manual for that ECM, and Here for the wiring diagram for your engine. They may help your search for the problem.

 

[Fun Times]

Re: mercruiser 350 mag mpi blowing fuse

Pretty sure this is not your issue here, but your serial number shows it is still open for Mercruiser service bulletin number 06-02 - orange Alternator Wire.

Possible Chafing of Orange Alternator Wire on 5.0L/5.7L/6.2L MPI Engines.
Situation
On the units identified above, an orange wire attached to the output terminal of the
alternator (the orange alternator wire) was routed by MerCruiser in one of two ways. One
way was correct, the other was incorrect.
The incorrect routing places the orange alternator wire between the oil dipstick tube and
the alternator. With that incorrect routing, it is possible that the insulating material will be
chafed by the dipstick tube or the alternator, which could cause the wire to fail. If the wire
fails, it could become an ignition source. See the "incorrect routing" photographs below.
The correct routing passes the orange alternator wire beneath the alternator, not in contact
with the dipstick tube, which eliminates the opportunity for chafing and failure identified
above. See the "correct routing" photograph following.
In addition to the two orange wire routings described above, many boatbuilders modify or
disconnect the orange wire to facilitate the installation of battery isolators. Boats that have
been so modified will not require the corrective action outlined below.

This usually will blow the 90 amp fuse on the engine starter. So with this said, you need to check all wires on the engine for chafing.

Good luck with it, And if you could, please let us know what you find, Thanks.

 

[Don S]

Re: mercruiser 350 mag mpi blowing fuse

I thought about showing him that service bulletin, but for the life of me, I could not see how it could possibly blow the fuse he has blown. I could see the 90A fuse blowing, but not the smaller one.
Of course, we also have no clue which fuse is blowing.

Ya gotta love finding intermittent fuse blowing shorts or draws without actually seeing it. The problem might be obvious to a trained eye.

 

[Fun Times]

Re: mercruiser 350 mag mpi blowing fuse

I with you Don, that is why i decided to say Pretty sure this is not your issue but!

We've all seen weird unusual things before so even though i'm pretty sure it's not it, you just never know till you check into it.

For me this would be a fun challenge to look into.

 

[Don S]

Re: mercruiser 350 mag mpi blowing fuse

For me this would be a fun challenge to look into.

LOOK being the operative word here, I always liked the challenges of this type job myself, when I had the boat to work on. But trying to find it on a forum. Totally impossible. when you can't "See" touch, smell, or use any other of your senses than reading a post.

Being intermittant, I would have the hatchs off the boat, someone else driving and I would be wiggling things, looking at the diagnostic computer, listening, etc. All at the same time.

 

[Don S]

Re: mercruiser 350 mag mpi blowing fuse

Digger, here is that bulletin that wasn't done on your engine in case you want to fix it.

View attachment 153718

 

[achris]

Re: mercruiser 350 mag mpi blowing fuse

..For me this would be a fun challenge to look into.

I'm sure the OP thinks it's fun too, when he's stranded out in the middle of the pond with fuses popping and no idea what the hell is happening... Yep, I just bet he says, "This is so much FUN!"....

Personally, I HATE intermittents... 'Hard' faults are so much easier to find...

What I really enjoy and find the greatest fun, is when the boat does exactly what it's designed to do and the engine performs faultlessly... THAT is my 'fun'....

Chris...........

 

[Fun Times]

Re: mercruiser 350 mag mpi blowing fuse

LOL, Hey i gotta make use of my forum name somehow.

Now let's stop hijacking this poor guys thread and see if we can help guide him along.

 

[ditch-digger]

Re: mercruiser 350 mag mpi blowing fuse

Hey, its always more fun when we work on somebody else's problem, right? I am going to hook ECM up to computer today and see what it shows, then dive into that sucker and see if we can find the problem. Thanks all, for the help and suggestions and sick twisted humor.

 

[ditch-digger]

Re: mercruiser 350 mag mpi blowing fuse

So here goes what I've come up with so far. The fuse that is blowing seems to be going to the fuel relay. I hooked up the computer to the ecm and it did not show a faulty relay fault. The question I have i have is could the fuel relay be bad and still not show up on the diagnostics? Any thoughts? Thx for any!

 

[achris]

Re: mercruiser 350 mag mpi blowing fuse

...The question I have is, could the fuel relay be bad and still not show up on the diagnostics? ...

Yes... I'll look up the drawing and get back to you (see what else that fuse drives)...

 

[Don S]

Re: mercruiser 350 mag mpi blowing fuse

Chris, I already gave him links to the manual and wiring diagram up in #7 reply.

 

[achris]

Re: mercruiser 350 mag mpi blowing fuse

Which fuse is popping? (2 are associated with the fuel pump)...

 

[achris]

Re: mercruiser 350 mag mpi blowing fuse

Chris, I already gave him links to the manual and wiring diagram up in #7 reply.

Yes I know... But there are 2 fuses associated with the fuel pump relay, and both are also supplying power for other things as well...