Blown ECM new or repair?

[fishman]

Hi, my name is Stephen and I own a Mercury optimax 200 year 2001 on 22 feet fishing boat.
On my boat I have a stainless steel fuel tank. Every year I experience leak from this tank. Everybody is telling me that the tank has no earth.. I asked a boat electrician for this advice and he told me to do an earth from the fuel tank to the negative pole ....and I did so :(
(I think he didn't know that my main switch, switch off the negative and not the positive! !!!)
Now after all this I went to start the motor and I forgot to switch on the main switch, then I switch on the main switch and straight away on my smartcraft many faults came on like: fuel level, oil level, block psi, tps, trim ......etc etc.

Now I think that I blown up the ECM. (Can this happen????)

IF YES!! How much it will cost a new ECM??? or who do you suggest to repair it? And to repair it how much it will cost me?

Please help me because I am at a stand still :(

[luv2gofast]

I would look at all of the wiring going to the smartcraft and keyswitch. You probably burnt up a small ground that goes to something. When you tried to start the motor with the main ground disconnected, the starter current probably tried to go through the small fuel tank ground and the ground for the fuel level sensor. It also may be the smartcraft gauge its self. Did you try to start the motor or just see all of the errors and no try to start? I don't know enough about the smartcraft stuff but maybe someone that does could comment. Can you can disconnect the smartcraft gauge and still start the motor?

[fishman]

Thank you for your reply I did start the motor and it starts quite well, but the idle is rough and it stays on 2000 rpm and the error still shows
I reset the codes with ddt but as soons as I switch on the ignition they reappear.

I checked all wires coming out from the ecm with the multimeter for continuities and they are all okay but yo tell you the truth I never checked as you suggested from fuel gage to smartcraft and that is the thing that I will try tomorrow.
Do you still think that the ecm still is in working order. (Please send me some good news :) )
Thanks again and I hope to hear more suggestions.

[luv2gofast]

Try to figure out what the ground path was with the master sw open. That is where I expect you will find the problem...hopefully that's not inside of the ECU. Sounds like it's running in "limp mode". May be because of a sensor read error. Does the DDT show reasonable values for all of the sensors?

[mn808gade]

do you have black batt switches?on this side of the pond I think ALL batt switches are RED and next to terminals it says (batt 1 +)(batt2+)etc.cant remember ANY boat switching ground wires on and off.54 years only means that I'mm forgetting more and more-th

[fishman]

Mn808gade: so let me know if I understood your comment, so you are telling me that the main switch should cut off the positive and not the negative right?

[fishman]

Hi Luvtogofast : I did exactly what you mentioned to do and still no luck :( when i start the motor did exactly the same what it used to do and for some reason I don't know how I still can see the rpm on the smartcraft, even when I unplugged from the motor. Do you have any suggestions? Thanks for your help.

[luv2gofast]

Sorry but that is about all I can think of. It would be nice if you could find an ECU to try before buying a new one. It's a lot of $ and you will be very disappointed if that is not the problem. Very unlikely that it can be returned.

[fishman]

A friend of mine have a mercury optimax 225. DO I do any harm to his motor if I put my ecu into his motor? Even if mine is optimax 200. So I can clear my mind if the faults keep appear on smartcraft.
In my opinion I think that is the best thing to do because if I do vice versa I might blown his ecu. Do you agree with me?