mjb

As a fairly new member to OSO, I am thankful for the amount of knowledge on this board that gets passed around. I'm hoping some knowledgeable FI guys can shed some light on this.
I have read several threads telling how important it is to keep your fuel regulator as close to the fuel rail as possible on a high performance engine. Most FI shops will tell you the same thing. Most generic fuel system layouts show the regulator AFTER the rail/injectors.
Prior to 1997, the 454/502 MPI's with VST's did have the regulator at the front of the fuel rail with the return line coming out of the rear of the rail. In 1997/1998, cool fuel replaced the VST..all in the name of making improvements. So why did mercruiser move the regulator all the way down to the cool fuel box?? I understand that the regulator that is still on the rail is just a dummy on some models and a dampner on others.
When upping a cool fuel engine to 500HP, has anyone moved the regulator and return line back up to the fuel rail ? Will this stop the needle bounce on my fuel pressure gauge? Is this worth doing or am I just wasting my time?

Raylar

MJB:

Those devils at Mercury locate a cheap non-adjustable pre-set regulator in the cool fuel box so their savey customers won't suppossedly be able to adjust fuel pressures possibly up for more power with modifications. This protects Mercury with their warranty and leaves you the customer with a slight problem after warranty. Simple solution, plug the return line that comes from the regulator in the cool fuel unit back up to the fuel filter at the filter. They usually cap the return line coming off the regulator on the fuel rail. Remove the cap or plug here and then connect it with a line to where you removed the return line from Merc's regulator in the cool fuel. This will allow you to adjust your own fuel pressure at the rail and will give you the ability to adjust it for power and changes. Make sure you disconnect and plug the vacume hose to the rgulator and adjust the fuel pressure. Then reconnect the vacume line. You can get a part and fuel line schmatic in the Merc. manual or go to Bam Marines website and download and print it out, it will help you understand the plumbing. As for the problems with the guage, this is because of pulsation in the pressure side of the fuel system. Install a pulse damper in the line to the guage and the jumping should stop.
Hope this Help!
Ray @ Raylar

mjb

Thanks Ray- I figured it was the lawyers that made that decision, not the engineers. I'm planning to do just what you recommend with one variation. The regulator currently on my fuel rail is just acting as a dampner now. The port(nipple w/ o ring) where returned fuel goes from the regulator into the bottom chamber of the fuel rail is solid. Rather than drill this out or replace it and add the return line to the rear of the rail, I think I will leave this dampner in place as is. I will use the service port just above it to plumb to a new free standing regulator that I will mount to the ECM box and then run the return line from this new regulator back to the fuel filter. I will also mount a permanant mechanical pressure gauge between the fuel rail and the new regulator to monitor and set fuel pressure.
Sounds like a quick, easy fix to me. Plus, its much easier to adjust the pressure from the top of the engine than upside down under the engine!
If anyone else knows of any problems this modification would cause I would really appreciate some feedback. thanks-

robyw1

Why do you want to adjust your fuel pressure? Are you leaning out? You can adjust it if you want but unless you have installed a free flowing exhaust, or other minor mods then you will be loading up the engine and wasting fuel unnecessarily.

mjb

Rob- I am doing fairly major modifications to my 502's so thats why I need to be able to adjust my fuel pressure. I talked to Mark at precision marine today and he suggested sending the return line back to my fuel tank rather than going back to the fuel filter. All of these mods are fairly easy and cheap...especially while both engines are out of the boat. Too bad I already wasted the time and money putting the adjustable reg on my cool fuel earlier this year.