2000 year 240 EFI pressure reg.

[Tim75]

on Merc 240 EFI, the fuel pressure regulator, located on top of the VST, made by Keihin. What is the purpose of the small hose that runs back to the block?

My pressure is running 65 psi. Seems my reg. is dead. I am in the process of adding an adjustable reg. ahead of the Merc reg. Then I can set 36 psi for about $35, instead of $300. Thanks, Mercury.

 

[Dr Honda]

Well... that's a great question. LoL

I've never really dug into that myself... but on the newer engine... that's called a "Vent Hose." AND... on your engine... you can do an off-line test with pressurized air, or fluid, and that hose isn't hooked to anything during that test.... I would say that it's also a vent. The only thing I would need to verify is what the nipple on the engine is hooked to. I believe it's just tapped into the plenum.


**EDIT**

I dug into every picture I had, and in the service manual. It' hooked to the top nipple, and it's just mounted in the throttle body aluminum. It's not tapped into the fuel rail. SO... I guess when the vac is high... it may lower the pressure a little... but otherwise... it's just a vent.

Since you are mounting an aftermarket regulator... it's really irrelevant. Plug the nipple on the manifold, and set it for 36 psi.

 

[Tim75]

I finally got the boat into the water today! Ran great! After a 5 min. idle away from the ramp, 4k rpm, then 6k! Never had 6k before. Max was 5600-5800. Clean injectors really do make a difference!

Another person had done this before, but he made a fitting to replace the Merc. reg. I went even simpler.
I installed the adjustable reg. inline before the Merc. reg. and let the return from that reg. run into the Merc. reg. Now if the Merc reg. sticks, I still have 35 psi. No custom fittings.

 

[Dr Honda]

Thanks for the follow up. Post a pic when you get a chance.

 

[Tim75]

Thanks for the follow up. Post a pic when you get a chance.

Boat's covered now. Pix this weekend.

I think you are right (as usual).-- After watching some youtube videos, it seems the top hose is a Just-In-Case connection- if the diaphragm fails, the gas has somewhere to go.

I still have a little "neatness" work to do on the installation.

 

[Tim75]

Pix of basic install- I am thinking of making a bracket to mount reg. onto 2 spare tapped holes on top of VST. Would vibration be a problem?

 

[Dr Honda]

won't be a prob for the regulator. But the gauge may not like it.