150 HPDI blowing 20 amp ignition fuse, can't find the short

[refimike]

I have a 2003 Yamaha HPDI Z150TXRB motor on my boat and I have ran into a problem that I can't track down. The 20 amp fuse that controls the ecu, ignition and fuel pump keeps blowing immediately at key on. This is a new condition that has not happened before. I have tried to isolate the issue thinking that it is a dead short and I individually disconnected each component that Iis wired to that fuse. I had a box of 20 fuses and would disconnect each thing then try to key on and even with literally everything disconnected I am still blowing that fuse. I tried to trace down any wires that ran from the fuse box to the ecu and found two wires that were chaffed and replaced those sections of wire but to no avail. I plan to remove the back cover off so that I can see if there is anything that could be blowing it but as of now it seems like its either in the wiring running to the ecu or the ecu itself. I don't have access to a service manual because I was in the process of trying to sell this boat as I have a new boat that is supposed to be delivered on June 15th and I really wanted to sell this one to help with the cost of the new one. I am wondering if there is anywhere else I should be looking for the short or since I can't seem to see any wiring that is suspect leading to the ecu is it possible that the ecu itself could have a short? I have really run out of options and can't find any mechanic that is halfway decent to take a look at it. Any help would be greatly appreciated.

[refimike]

And to clarify, the only component that I didn't disconnect was the ecu because it was starting to rain and that would have been too involved to do before it started to downpour.

[fairdeal]

https://docdro.id/rgh6g5H

[fairdeal]

https://www.littleurl.online/f1iHVglg

[refimike]

Thank you for the wiring schematic. Can you point me in the right direction to go from here. I see three different 20 amp fuses in this drawing but I am not seeing which one is one for the ecu fuel pump and coils. Once I find that a little help on where to go from there would be great. I know little about electrical schematics but I do know some and can somewhat decipher but will probably need some help.

[boscoe99]

The yellow wire provides key on battery power to a number of components on the motor. Why not start by isolating those components to see what happens?

Perhaps starting with the components at the dash.

[boscoe99]

Maybe this will help. Hopefully, it won't make things worse.

[refimike]

Thank you Boscoe. That wiring diagram is a bit too tough for me to decipher but maybe this will help.

I have individually disconnected each circuit at the dash at each switch individually and tested with a new fuse each time and at key on each time I would blow the fuse. Even when all were disconnected I was still blowing the fuse. At one point I think I had basically every single injector and coil unplugged, as well as almost everything else under the hood unplugged like the shift switch, fuel pump, o2 sensor, TPS sensor, crankshaft position sensor and so on and was still blowing the fuse immediately at key on.
Only time I don't blow the fuse is when I disconnect the wiring harness under the cowl I no longer blow the fuse but I am not sure that if I do that that the engine even knows that I have put the key to on so I am not sure if that is relavant.
And by harness I mean the 9 or 10 pin round harness that is in under the hood on the starboard side of the engine.

The only thing I have not disconnected at this point to check to see if I am still blowing the fuse is the ECU and I believe the injector driver.

[boscoe99]

To save on fuses, I would have disconnected all of the components that get power via the yellow wire. Turn the key on. Fuse should not blow. Then start connecting the disconnected components until the fuse blows. At which time the guilty part would have raised his hand.

[boscoe99]

It might be time to take the motor to a Yamaha mechanic.

[boscoe99]

With the ten pin coupler on the motor disconnected, there is no way for battery power to ever make it to the yellow wire. Thus the fuse won't blow.

[refimike]

To save on fuses, I would have disconnected all of the components that get power via the yellow wire. Turn the key on. Fuse should not blow. Then start connecting the disconnected components until the fuse blows. At which time the guilty part would have raised his hand.

Are you able to tell which all components are connected to the yellow wire? I can't decipher that from this schematic.

I would definitely take it into a mechanic if I could find one that was willing to work on it in under 6 months wait time.

[boscoe99]

Are you not able to see the components that I encircled in red?

[refimike]

oops.... I didn't realize that was you who made those circles..... I feel dumb...
Ok, that gives me a great start, I will get on that right away and get back to you right away with what I find. I can understand enough to find those items. THANK YOU!

[boscoe99]

Another thing to try is to disconnect the ten pin connector at the motor. Then jumper the red wire pin on the motor side to the red wire pin on the harness side. Then turn the key on. Does the fuse blow?