VST very hot after ECU Bypass / 2000 Mercury 150 efi

[pancakes]

I have a mercury 150 efi on which i have bypassed the ECU fuel pump driver via the purple wire and keyed relay kit. Motor ran okay but started a little rough and would not idle in the water without adding a bit of throttle.

after a frustrating, if not dangerous day on the water, i neglected to turn off the key switch at the ramp and put the boat away with the VST running continuously for about an hour. engine smelled like fuel and the VST itself was VERY hot. The primer bulb was soft too, possibly indicating an empty VST. Is the VST pump toast? the motor still runs but I haven't run it on the water yet.

thinking now that a ECU rebuild was the better(but much more expensive) way to go.

 

[alldodge]

Not an OB guy, but have had VST on I/O's. Bypassing the ECM/ECU IMO is not a good choice. I'm glad no one was hurt and nothing damaged.

Agree, rebuild/replace is the way to go. The VST may not be toast, because all its trying to do is keep the pressure at spec, the issue is the motor was using no fuel. Using no fuel means there was no cooler fuel coming in to help cool the pump. If it can build to spec pressure, then pump is good.

The pump is only one piece of the system, and the regulator is the other to keep correct pressure

 

[Dukedog]

strange?.. know of several runnin' with tha relay stuff for a very long time now… from production 150's ta 225 pro max and never heard of any problems... but they are all switch box motors (non-cdm) and haven't left key on that I know of..... sounds like ya may have some "leaky" injectors....

curious? how do kill tha motor after ya put it on tha trailer?

 

[pancakes]

I kill the motor via the ignition switch as normal because the purple wire is hot when ignition is on, dead when it's switched off. if the motor runs normal, it's impossible to forget to do this and every thing turns off. but in my case the the motor konked out just as i pulled into the ramp which sent me into scramble/fend mode trying not bump the dock.

really, i'm just trying to get a handle why the motor runs so crappy in this new fuel pump configuration(no ECU) and whether i've introduced a new variable but letting the VST run dry for an hour making it super hot. and it was HOT. like, it'll burn you hot.

I'm going to re-hook the intermittent ECU and see if anything improves.