help, new fuel pumps and pressure still below specs 2004 5.7 MPI

[2004 searay]

hi, i have a searay with a 5.7 MPI engine, bravo drive, serial # ow027371, this has the fuel pump under the port side engine mount. i had a problem last season with no power and diagnosed as low fuel pressure, 28psi and 32 with reg unplugged. over the winter i replaced both pumps with OEM units and the fuel regulator and filter screen down below. now i fire it up and i am only getting 30PSI and 38 with regulator unplugged. . i checked the fuel supply line and thats ok, ran a seperate tank of fuel to the input line, tested the power to the low pressure pump, and the high pressure pump i can hear run so i know the power is getting to that one. i am so sick with this issue, i spent a lot of money on OEM parts and to still have this problem is so discouraging. i also tried 2 different fuel pressure testers, both give the same info.

 

[alldodge]

Welcome
What is the part number of the regulator?

 

[2004 searay]

860349A 1​

which when i looked it up thats the # i came up with but now states :
Fuel Pressure Regulator Regulator mounted on fuel cooler
No color mark Fits MCM/MIE 7.4L/LX MPI, 454 Mag MPI, 502 Mag MPI & MIE 8.2L MPI

the one it calls for is :
861126A1 Fuel Pressure Regulator

Mounts on fuel cooler.

Fuel pressure regulator 861126A1 is for use on MerCruiser 4.3L, 5.0L, 5.7L and 6.2L MPI stern drive and inboard engines with ECM 555. Also for use on MerCruiser 7.4L MPI (L29), 454 Magnum MPI, 496 Magnum and HO, 500 EFI and 8.1S and HO engines. See your owner's manual or service manual for specific application and instructions


i know the part # is wrong but based on the description, it should work, no?

 

[alldodge]

860349A1 Cool Fuel Gen 1 Mallory 9-33207 (36 psi)

861126A1 Cool Fuel Gen 2 (43 psi) BLUE Mallory 9-33206, Merc 892681

Not enough pressure and if it wasn't a MPI with all the sensors it may have burned a piston from a lean condition

 

[chs marine service]

how much pressure do those HP pumps put total? sounds like they use the same pump for multiple systems.

 

[2004 searay]

im sick to my stomache. i cant believe i have to pull this motor again when i broke my ass doing it the 1st time.

 

[alldodge]

I guess its way to hard to get at pump in the boat?

 

[alldodge]

how much pressure do those HP pumps put total? sounds like they use the same pump for multiple systems.

Pumps will output above 60 psi if unregulated

 

[2004 searay]

I guess its way to hard to get at pump in the boat?

the pump i located behind the port motor mount. and there is no access in the area to work. the only way to access it is to lift the motor.

 

[dubs283]

Have you inspected the fuel supply to the fuel pump?

A fuel vacuum test will indicate an issue with the fuel line and fuel tank supply.

 

[Lou C]

A 2004 boat is old enough that the anti siphon valve could be bad, fuel pick up screen clogged etc. Ever try testing pressures with a remote tank? I’d for sure do that before pulling the engine again.
It’s stories like this that make me glad I still have a simple engine with a mechanical fuel pump ($75 to replace) and a 4 bbl Quadrajet ($60 to rebuild).
And if I re power it that’s how it’s going to stay.

 

[alldodge]

Good grief guys it's not a fuel supply issue it's a fuel pressure issue

 

[Lou C]

Other than low voltage to the pump and low fuel volume to the pump if everything is new with the correct parts installed what else causes low fuel pressure?

 

[alldodge]

Other than low voltage to the pump and low fuel volume to the pump if everything is new with the correct parts installed what else causes low fuel pressure?

The regulator, Please read the thread

 

[dubs283]

Good grief guys it's not a fuel supply issue it's a fuel pressure issue

OP states fuel pumps and regulator replaced with oem

Untethered vacuum reference pump should supply above spec pressure regardless of regulator

A fuel pump with no restrictions regarding supply ought to produce viable numbers for testing. OP's does not

It's time to investigate fuel supply (to the pump) issues

 

[Lou C]

What I said. I recall reading that Merc revised these cool fuel modules because of problems in the field, I wonder if that has anything to do with the OPs problem of low fuel pressure. Are you sure that the parts used are correct?
Also while there may be 12v at the connector what happens when the load of the pump is on the circuit? The pump(s) draw how many amps? What about the terminals for the relays? This was a problem on certain V/P EFI engines, low quality relay holders with corroded terminals = high resistance.

 

[alldodge]

OP states fuel pumps and regulator replaced with oem

Untethered vacuum reference pump should supply above spec pressure regardless of regulator

A fuel pump with no restrictions regarding supply ought to produce viable numbers for testing. OP's does not

It's time to investigate fuel supply (to the pump) issues

No

Regulator which was installed is
860349A1 Cool Fuel Gen 1 Mallory 9-33207 (36 psi)
it's a 36 psi Reg and he's getting 30 to 38 psi on gauge. Given all gauges are +/- a bit, shows Reg is working correctly

Motor need a 43 psi Reg part number
861126A1 Cool Fuel Gen 2 (43 psi) BLUE Mallory 9-33206, Merc 892681
which is the correct part number for his motor serial number

How is this a supply issue?

 

[dubs283]

How is this a supply issue?

Again, regardless of presently installed regulator the pump should provide above maximum spec pressure when the vacuum reference line is disconnected

OP has performed this test and the fuel pump (oem) hopefully installed correctly does not provide spec pressure

Not saying you're wrong about the regulator, Im thinking a pump fed weak supply will provide weak supply, ymmv

 

[alldodge]

Guess we'll just agree to disagree

Pump and Reg is new ans OEM

Reg controls max pressure. Only way to get more then max pressure is to block off Reg return back to fuel filter

 

[dubs283]

Only way to get more then max pressure is to block off Reg return back to fuel filter

If equipped as such

Mercury didn't utilize this system much. Iirc it was used on a 7.4 mpi gen v with a vst and mechanical fuel pump. This is pretty esoteric

We don't know OP serial number/setup, guess we can guess

Did you ever locate the seal on your monitor bottle cap? Pardon the digression