I have read many posts on here about removing the VST system from the 502 MPI but most the posts are vague or not applicable to my application. I know most of you use the A1000 in line fuel pump, which is great, but I am just running stock power.

My question is: Can I use the in line fuel pump in this link?
http://www.jegs.com/i/Autobest/035/HP4456/10002/-1
(Good for 45-65 PSI & 40 GPH). Just have to see if my stock fuel lines are larger than 5/16. I think they might be so this could cause a problem.

Also, I would remove the sea water pump mounted mechanical fuel pump as well as the VST tank, and run a line directly from the new in line pump to the fuel water separator and then to the fuel rail. I would mount the pump on the stringer a few feet away from the fuel tank. I think I will also need to run a return line back to the fuel tank which might be tricky since I don't have an extra port in my tank. Do I even need the return line? Will this pump be ok with the back pressure built up from the regulator? Can I keep the stock fuel regulator?

Please let me know if this setup will work? I finally want to trash this VST system. I've been inside it too many times!!! Not to mention the mechanical fuel pump I've replaced 3 times over the years.

I cannot help with your issue; however, I'm interested in how the VST has failed you. What have you been in the tank for so many times? And are you saying the lift pump has gone out 3 times? What was the cause?

I'll subscribe to the thread as my 454's have the same fuel system as you; however, other than cracked VST diaphragm's and dirty pick-ups I haven't had any issues. The boat was 20 yrs old when I bought it and doubt anyone had been in them. I also found a source for VST fuel pumps with strainers for $70.

So the VST fuel system in my opinion is very over-engineered. I've had the mechanical fuel pump fail 3 times and I've owned the boat for 7 seasons. You need to pull the set screw out of the side of the mechanical fuel pump and check the oil. If oil and gas are mixed, the diaphragm is bad and the whole pump needs to be replaced. The gas will wash out the bearing. Furthermore - I had one go out so bad before that it took the $600 sea water pump with it. I open the VST can at least once a season due to a clogged filter or ruptured diaphragm. If a diaphragm ruptures then you start dumping raw fuel into the intake and washing out cylinders. The needle and seat has also stuck before on me. If you read around the forums, the major complaint about this whole system is vapor locking. I actually have not had any issues with this since I've owned my boat.

Can someone also reply and let me know if 40GPH is enough volume to feed my engine? I see the pump is rated for 45-65 PSI which will be enough for the engine but what about the 40GPH?

Thanks for the info. I have read about vapor locking and I don't experience it either. I did pull the screw on the side and had gas in the oil; however, none in the inspection tube so I drained and refilled with oil. I guess I need to be on the look out for the bearing going kaput now (good info.)

As far as having to open the VST once a season, is it possible you're using ethanol fuel and breaking down components pre VST that is causing those issues? I opened both VST's to find a diaphragm's dry rotted 1 screen 1/3 plugged and the other fully plugged, but as far as I can tell they were never previously opened and the boat is 20 yrs old with 235 hrs on it. The supply lines from the tank to the lift pumps were original as well and probably crapping up the screens.

I look forward to the info. You gather here as I may lean toward the same solution as you to simplify the system. Thanks for the info!

I have the same setup, I think at wot the 502 is rated at 40gph, so you may want more pump than that.
I think pretty much all mechanical pumps leak fuel and a good idea to check and change oil at least seasonally.

My 500 + HP 502 is using one Mercruiser 861156A1 cool fuel pump. Now to get into the motor mods but the cool fuel standard pump puts out more fuel then this motor can use at WOT. The Airtex pump number is E11004 and they make the pump for Merc.

Mods for you to consider if you remove the VST. The VST has the fuel return going back into the VST and the regulator is in the VST. If it is removed then the return needs to go back to the fuel filter (Merc way) or to the tank (best way). Using cool fuel will put the regulator on the cooler. The rail can be modified and return fuel back to the tank.

My VST was removed during the rebuild but I had not issues with it, I just wanted to go with newer stuff and easier to maintain

Thank you for the reply. I knew I would have to somehow run a return line. The spare port on the fuel water separator is too close to my exhaust manifold to be able to thread a fitting into it so likely will return back to the tank VIA fuel fill adapter that cp performance sells. I was unaware I would have to run another regulator? I thought the regulator on the fuel rail would manage the pressure. Do you have any input on this? So do I need to run a regulator before the fuel rail as well as the stock regulator in the fuel rail?

You might not need another regulator if there is one under your fuel rail, it would be item 15.

http://www.mercruiserparts.com/bam/s.../31910/2336/10

If your regulator is there then you just need to run the return line back to filter or tank

Have you found this thread in your research? There's return and regulator info. Therein. http://www.offshoreonly.com/forums/g...eromotive.html