picca00

I have a 96 454 mpi non magnum motor and the VST tank was removed. I have a cool fuel set up on it and 2 regulators, one on fuel rail and one fuel cooler. There is also 2 return lines one from the rail that goes to gas tank and the one on the fuel cooler that goes to the fuel/water separator. Problem is I can't get pressure above 34 psi at any point. The fuel pumps are fine. I think the problem is that I am returning to much fuel... I can see the return from the rail flow back into my gas tank at a pretty good rate, seems a lot to me but not sure about this.
I was thinking to tap and plug the out line on the fuel rail and have no return to tank and just let the fuel cooler regulator keep returning to the separator? I need some help with this and any ideas you pros can think of. Do I need an adjustable regulator or 2? That doesn't make sense to me.. Please help guys season here...
Thanks, jay

FIXX

iTrader: (2)

you can try putting a restrictor in the return line like we use to do on mechanical fuel injection ..here is the doohicky that the pill goes into and keeps thefuel in the lines ..you will have to get differant size jets to get the rite pressure..

http://pitstopusa.com/i-6700000-hilb...ass-valve.html

lakematdude

A few thoughts come to mind reading this, One is, are you sure you have the correct fuel pressure regulator/s?

Here's some specifications of the regulators for you from a merc service manual,
V8 7.4L, 8.2L, MEFI-1, (MPI, VST, MerCruiser MPI intake, Keihin injectors).
All 7.4L & 8.2L Unknown color, 36 psi (248) 805227A 1 Regulator on fuel rail. Hose fitting points toward port side.
MPI models.

V8 7.4L, 8.2L, MEFI-1, (MPI, Cool Fuel, MerCruiser MPI intake, Keihin injectors).
All 7.4L & 8.2L Yellow/ 36 psi (248) 860349A 1 Regulator on fuel cooler. Black ring on hose.
MPI models Orange fitting. Regulator on fuel rail does not control fuel pressure.

The year with the VST used 36 psi regulators and some of the cool fuel systems used 36 psi regulators as well.

You probably have two 36 psi regulators on there.

If both systems are still original then to confirm this theory, you would need both mercruiser engine serial numbers to look it up. One from the VST system plus the one from the cool fuel system.

Another thought would be, are the fuel injectors (Keihin injectors) from the VST engine rated to handle more PSI?

Lastly, on later MPI model engines, the regulator on the end of the fuel rail is used only as a dummy fuel pressure pulsation damper to ease fuel pulsation to the injectors seen in item #13 for example only,
http://www.mercruiserparts.com/Show_...+and+Fuel+Rail

Two regualtors? Not sure what trouble that would bring if any? You may need to buy a dummy regulator for the rail.

What's the reason you need/want more fuel pressure?

Side Note, To help avoid fuel vapor lock, it's always a better idea to return to the tank vs the filter assembly when possible.

picca00

I need more pressure because I'm running lean I think, plugs are very white and sometimes when fully loaded for wake boarding I get a backfire through exhaust. I know it's not making enough pressure.. 34 psi is a little... I also have a green ring on my regulator on the fuel cooler... Thanks for the input keep it coming...

lakematdude

7.4L MPI, Olive Green 43 psi (296) 802632 [GM]. Bravo & Inbrd, Band on Tip

Keep in mind that you have a second regulator on the rail that could be lower psi. Can you tell the color of it as well?

What brand/#'s spark plugs are you running? Double check timing for safety. Engine temp is? Thermostat temp is?

picca00

I'll have to check fuel rail regulator for a color code, all black from what I can tell. Timing is good, engine temp around 160, have to check plugs....
Looking for the best solution, the new fuel rail only have an inlet and return is done on cooler so that why I was thinking of plugging my return line on the fuel rail...

picca00

What's Eddie from young performance got to say? He seems like a go to guy foe efi's. you out there Eddie?

picca00

Not a lot of help just yet, was out yesterday, changed fuel filter and added fuel injector cleaner to the main take and the filter. Didn't help at all, still 33-34 psi at speed, at idle the pressure was a little shaky. Boat runs good other then that... Just don't want to be to lean