Yamaha f90 iac getting hot

[Mike781matco]

I appreciate it. Also just noticed the tach is no longer working. I’m starting to suspect the ecu. I live in central fl and we had a nice lightning storm that damaged some electronics in my home a few weeks back. I’m thinking the boat might have been affected. Tach worked and didn’t notice any issues before the storm.

[boscoe99]

I did not want to say so but I am suspecting the ECU also.

There is nil theory as to how the ECU and the relay assembly works. That I can find anyway.

From reviewing a wiring diagram and the relay internals itself, it would appear that key on power will close the main relay within the assembly. Closure of that relay sends power to the ECU. It also sends power to a junction block from which power is sent to other components.

The ECU then applies a ground to the fuel pump relay, which closes and then allows battery power to go to the HP pump.

Power is also sent to the relay control circuit by the ECU via the green wire. What I will call the tachometer wire.

My guess is that upon the key being turned off, the ECU continues to provide power to the main relay for X period of time. How much time I know not. At the completion of X time the ECU will terminate power to the relay via the green wire.

It would appear that your ECU is not turning the main relay off.

[Mike781matco]

Agree. It’s not turning off. Once the first key on cycle energizes the fuel pump (that I hear it doing) it stays on no mater how many times I cycle the key off and on. I don’t hear the pump come on until process is reset. (Batt off batt on key on fuel pump runs). I did also check all grounds on the engine. I ordered a ecu and main relay. 800$$$$$$ from partsvu for both. I need to get it right soon, mini season is coming fast! Also hoping the tach isn’t messed up now, but those are cheap enough. I’ve read your posts about wall warts and I don’t have any laying around to test it.

[Mike781matco]

Update. New ecu installed. All is working like it should. Thankyou for the help boscoe

[boscoe99]

Thanks for the feedback. Glad you resolved your problem. Even if it was costly.