2007 Mercury 25 four stroke efi problem??

[clayton bigsby]

I went fishing the other day and hit a stump while idling, motor died will not run. I did an overall check nothing stood out, so i did a compression check, check the firing on the motor all good, so i check my fuel pressure 0% so check the fuel pump it was ok but the high pressure fuel pump inside the vst tank was not running. Took my vst tank apart and check my high pressure pump it's not getting any fire to it, so i put 12volts direct to the pump and it started to run. So my question is what runs the high pressure pump there is a blue wire, then a blue wire with a black tracer i'm assuming it goes to the ecu? If anybody can give my some direction on what else to check i would apperciate it!

 

[guyjg]

Check all electrical connections, switches, relays, sockets, etc. because something was knocked loose by the impact.

 

[Riphonda]

I went fishing the other day and hit a stump while idling, motor died will not run. I did an overall check nothing stood out, so i did a compression check, check the firing on the motor all good, so i check my fuel pressure 0% so check the fuel pump it was ok but the high pressure fuel pump inside the vst tank was not running. Took my vst tank apart and check my high pressure pump it's not getting any fire to it, so i put 12volts direct to the pump and it started to run. So my question is what runs the high pressure pump there is a blue wire, then a blue wire with a black tracer i'm assuming it goes to the ecu? If anybody can give my some direction on what else to check i would apperciate it!

First off, please save the “this is an 8 year old thread dude” comments. Please and Thanks! I am documenting for others to reference; this seems a common issue with Nissan/tohatsu/ Merc 25 and 30 EFI engines.

VST and high pressure pump are powered by the ECU. I had the same issue. New ECU fixed the problem but cost $850. The ECU seems to control the pump velocity by changing the resistance to ground side of pump when running/ based on input from engine sensors.

If you put 12v to the pump/ VST independently the motor will run as normal. Not sure if there is any danger or risk of burning up the pump on this but I would imagine you could power the VST from ignition circuit and have some success. Before another $850 I may try this!

This just happened to me again and wanted to share. Not sure I’ll pony up another $850 for another ECU... Thus motor hardly has any hours on it. Damn shame. Next time it’s a Suzuki instead!