Mp3 400 Lt working only without main fuse (hidden fuse)
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Member
Mp3 400 lt ie 2010
Joined: 21 Nov 2020
Posts: 5
Location: London Mitcham
Sat Nov 21, 2020 1:31 pm quote
Hello everyone! bought recently mp3 400lt unfortunately it had charging problem so i found and replaced main fuse in starter solenoid. It didn't helped and bike start stalling and going on low revs only.

Bought new battery
I replaced voltage regulator still same issue
Replaced stator (as it gave me slightly lower voltage than it supposed to) without luck of repairing

After that i have found that when i disconnected main fuse it revs fine and it rides without problem but its ofcourse not charging

Replaced starter solenoid and all relays with new one
Cleaned most electrical contacts and looked for potential short on the cables but can't see any...

Replaced right hand switches
And now i feel powerless as i can't see what else it could be

I have cleaned throttle body and whole intake
Replaced oil and filters

Found out that it can be faulty seat sensor so i bypass it with 2.7k Ohm resistor and it still not working

Any idea where i should look next? Or is it piaggio dealers job only now?
Moderaptor
The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
Joined: 26 Aug 2007
Posts: 39129
Location: Pleasant Hill, CA
Sat Nov 21, 2020 5:42 pm quote
Are you *sure* you checked the actual main fuse and not the spare, which is alongside it?
Member
Mp3 400 lt ie 2010
Joined: 21 Nov 2020
Posts: 5
Location: London Mitcham
Sun Nov 22, 2020 1:33 am quote
Checked the right one 100%. If the mp3 will work only with spare fuse out of holder that will be even more bizarre
Moderaptor
The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
Joined: 26 Aug 2007
Posts: 39129
Location: Pleasant Hill, CA
Sun Nov 22, 2020 8:49 am quote
Ah, I mis-read your post, sorry!

As this has been there since you acquired the bike, there may be something that a PO managed to mess up.

I'd be measuring the o/p of the new regulator while the main fuse is out, and the regulator is connected to the old battery. Some extra lash-up wiring required of course...

It's just possible both the old stator and the new regulator are faulty, but I'd be looking at the solenoid to check the wires are actually on the right spades. One or two bikes even made it out of the factory with that wrong.
Member
Mp3 400 lt ie 2010
Joined: 21 Nov 2020
Posts: 5
Location: London Mitcham
Sun Nov 22, 2020 2:28 pm quote
Thanks will check that.
Any chance someone can provide me with photo of their selenoid connected to see colours of cables connected please?

Today i noticed that i have a bit weird noise from the engine when fuse is on and it is quite when fuse out. It sounds slightly like electric motor with constant power

Do you guys think that starter motor working constantly is possible without loud grinding noise from enhine and can couse issue with low revs with main fuse in?

What exactly is main fuse protecting and where its after fuse side goes to

Appreciate all help
Moderaptor
The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
Joined: 26 Aug 2007
Posts: 39129
Location: Pleasant Hill, CA
Sun Nov 22, 2020 4:10 pm quote
I think you've nailed it. Get those wires in the correct place!
Hooked
Piaggio MP3 500
Joined: 21 Nov 2017
Posts: 296
Location: Austin, TX
Mon Nov 23, 2020 7:17 am quote
Yes, the wires are backwards on the starter relay. If the wires are backwards, the charging circuit goes directly to the starter motor, and causes it to spin when the generator system works (bike is running). That's the electrical noise you hear. Swap those terminals!
Member
Mp3 400 lt ie 2010
Joined: 21 Nov 2020
Posts: 5
Location: London Mitcham
Fri Nov 27, 2020 5:00 pm quote
Cables swapped but they burn main fuse instantly. I have managed to dopower draw check on the fuses and can see that i have bigges draw on fuse number 5 (fuel pump, ignition coil, injector and radiator fan relay) so I think problem lays there.

Is there anyone here who can check how many Amp their fuse number 5 draw? I have almost 4 amps on there where rest of them is all under 1amp
Moderaptor
The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
Joined: 26 Aug 2007
Posts: 39129
Location: Pleasant Hill, CA
Fri Nov 27, 2020 6:06 pm quote
Long shot - have you checked the solenoid hasn't welded its contacts shut? This is quite a common thing to happen on the smaller 80/90A relays used in Vespas and some other Piaggio bikes - but I've not heard of this happening to an MP3 so far. However, it IS a possibility.
Member
Mp3 400 lt ie 2010
Joined: 21 Nov 2020
Posts: 5
Location: London Mitcham
Sat Nov 28, 2020 9:53 am quote
Replaced selenoid doing same thing unfortunately. I belive that my ecu is having problems as soon as it gets power above 12.5 volt... no other way to check it than visit at piaggio dealer i believe
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