Strange Starting Issue

[Delorean6855]

Hello, recently joined the forum and grateful it exists!
Have a 2004 Mariner 360 w/6.0 Crusaders. Went to start them up the other day and the port engine would crank but would not start. When turning the ignition to ON, no audible alarms could be heard and the malfunction lights did not illuminate either. Puzzled over it for a bit, checked the usual stuff and just on a whim, I advanced the throttle to full and back to idle...and the alarm beeped and the lights went on. Cranked it and engine fired up right away. So am perplexed...the only thing moving the throttle would affect is the throttle position sensor... is it possible that there is a short or something in that which is causing a power loss to the ECM et al? Anyone else encounter a similar experience? Thanks!!

[bud37]

Welcome to the forum.......well that is very interesting.......I will just throw out an opinion here.

My guess if the tps is shorted somehow then it would shut the engine down on return to idle. The ECU you have may have a reset function, and I say may have...that would require Key on then advance throttle to max and back. Just a guess unless what happened was just a coincidence.You are partially right, the ECU would see the TPS advance to max and back.

There is lots of info online about the ecu functions of your particular version with some quite complicated explanations of all the interactions in the control circuits.

Have you operated the boat boat since ?....in the meantime, check all your grounds and connections....if something further goes on you will have to do that anyway.....good luck.

[Delorean6855]

Thought I should update this... the issue turned out to be the FireBoy control board. Once replaced, issue never returned...

[km1125]

Source of the post Thought I should update this... the issue turned out to be the FireBoy control board. Once replaced, issue never returned...

That's interesting. Thanks for posting the update.

I wonder if moving the throttle was some kind of code for "clear error" to the fireboy board or an "ignore fireboy" command to the ECU?

[Delorean6855]

Wish I knew...but the board was somehow cutting the 12v ignition between the key and the engine. It was very random but kept getting worse. Now I trying to figure out an the idle hunt (on every start) issue on both engines... I think I spend more time doing repairs and maintenance than actually using the boat