Yes, your Reg is good

Can do the test with the module connected, but will need to hot wire the fuel pump
Connect gauge (At least 100 psi) to fuel line coming from the pump
With Reg installed turn pump ON and pressure should hold steady.

If Reg is removed and hole is blocked with plate and gasket, pressure should be at least 60 psi with pump ON

Can also do it with pump removed on the bench and supply gas from a can. In all cases (except for test with Reg installed) need to bleed off the air for accurate test

Hey all. I have now inherited this problem! I bought ABL1111's boat and have been trying to diagnose a hard start/low power issue as it seems he may have been too. My gauge tells me 20 psi fuel pressure at idle and above (neutral. out of water). Is there a link to somewhere to the troubleshooting steps for low fuel pressure? I cant find anything in the manual.

If you pinch off the return line (from pressure regulator back to fuel filter head), while the pump is running (have to jump 12V to the positive side of the fuel pump relay), and the pressure increases, then the regulator is bad. Prior post by ABL seemed to indicate regulator was OK with air test so you probably just have a bad pump.

Thank you. Would that be a pretty definitive test for the main fuel pump? If it doesn't make pressure that way, the pump is bad?

Also, I find it odd that there is a regulator on the fuel rail as well as at the cooler/main pump. Would I need to take that one out of the equation to accurately test the fuel pump?

The regulator on the rail was a holdover from the old fuel system. When the "cool fuel" system on the lower port side of the motor was implemented (instead of the old VST system), Merc just put a blockoff in the fuel rail that made the old regulator useless (they then renamed it a pulsator). The regulator on the rail is a dead end. You don't need to touch it to test the fuel pump.

Definitive, well, mostly, yes. If you jumper 12V to trigger the pump, and while it's running, you pinch the return line and you can't get to 60 psi, the pump is weak / failing. A healthy pump should be very capable of hitting 60psi with the return line pinched off (and be sure to *immediately* release if you do in fact see 60, you never want to exceed that pressure.

Awesome. Thanks again. I did notice that the "return" was plugged after that reg. Funny tho. If you want to you can still pay $369 for it!

So now. Fuel pumps. The OEM one is NLA. Is there one we like better than the Sierra? I see the prices are all over the place, and I assume quality somewhat follows that number. I typically don't buy junk if I can avoid it.

I put in a cheapo from "the ROP shop", it works fine, delivers the same pressure as the OEM pump on my other motor. Durability remains to be seen, it's only been a month or so. Usually cheap is cheap, but I'm not convinced that all these pumps aren't coming out of the same Chinese factory anyway.

Pinched the return at the filter housing. Almost immediately pegged a 100 psi guage. Seems like the pump is good.

Blocking off the return will cause the pressure to exceed the Reg setting and damage it. As you have found the return was plugged to try and compensate for a weak pump.

You can still get the old pump and Reg, just not from Merc. Merc sells only the conversion kits
The pump use to be made by Airtex

I'm not sure I follow. According to his test, my pump is good and I need a regulator, yes? If it makes 100psi with the return pinched, and 20 psi with it open, it seems like the regulator has failed, but the pump is good?