Low fuel pressure on 350 MAG MPI

[toy4two]

Hi guys.

My Mercruiser 350 MAG MPI w/186 hours on it cannot get on plane, its maxes out at around 3000 RPMs. To fix I've been throwing parts at it since the local mechanics can't look at it for 3-4 weeks. It has a Cool Fuel II 2 system without the paint flaking issues. The engine reads 30 PSI at 1800 RPM instead of 43 PSI at 1800 RPM per spec. Idle/temp/oil pressure all excellent.

I've replaced:
Cap
Rotor
Wires
Plugs (looked perfect brown burn no fuel/soot)
Inline fuel filter
Fuel Water separator
Low Pressure fuel pump
Fuel pump relay
Fresh fuel with "enzyme" ethonol water remover added
No antisiphon valve on boat
New gas tank vent

The only parts I havent' swaped, but have brand new in hand are the fuel pressure regulator and the high pressure fuel pump. I have jumped the relay 30 and 87 pins and hear the high pressure fuel pump start.

My VesselView Mobile shows no codes and there is no beeping from Guardian. Does anyone have any clue what else is likely to be the problem with my motor? It worked fine just 2 months ago.

 

[wellcraft-classic210]

1 idea -- Can you measure the fuel pressure ?? That can be pretty telling if its a fuel delivery issue..

 

[toy4two]

1 idea -- Can you measure the fuel pressure ?? That can be pretty telling if its a fuel delivery issue..

it's 30 PSI at 1800 RPM and manual states it should be 43 PSI at this RPM.

 

[alldodge]

What is the engine serial number?

Also how long have you had the boat and did this just start?

 

[toy4two]

What is the engine serial number?

Also how long have you had the boat and did this just start?

Serial number: 0M627854

I've owned the boat about 3 months, and the last month this started.

 

[alldodge]

Assuming since you said no paint chips, then assuming you have an Alpha drive?

 

[toy4two]

Assuming since you said no paint chips, then assuming you have an Alpha drive?

Bravo III drive. The paint flaking is on the Cool Fuel III system, I have the Cool Fuel II system on my boat. In fact I have the plastic cover for it in my hand right now

 

[alldodge]

Your motor has 2 fuel pressure regs, but the one on the rail is basically a damper (smooths out the fuel pressure pulses). The other is on the cool fuel module (item 13)

https://www.mercruiserparts.com/bam/subassembly/31748/8093/60

This reg is there to control pressure, and send the rest of excess pressure back to the fuel filter. My thought is this is your issue, but need to verify. Remove the reg (make sure not to loose item 14, screen) and use a air supply with a control regulator. Apply pressure to the port where the screen was and see where pressure releases. It should be 43 psi, but if its lower, then the reg is the issue

 

[toy4two]

slowly recovering from my dizziness and headache from "standing upside down" in my bilge with fuel fumes for the last hour...

I'm 2/3 of the way done removing the Fuel Cooler II box and will put in new high pressure pump and regulator next.

 

[toy4two]

[No message]

 

[toy4two]

The only way to do this job is lay life preservers over the engine then put a towel or run over them. Use that to lay on top of the engine. Have a helper and expect it to take four hours. Cutting the thermostat housing S hose to fuel cooler is pretty much the only way I could disconnect it. Here are the instructions I followed but instead of pulling forward I had to pull backwards and lots of ya king to get all the hoses out. The more cooking hoses you disconnect the better:



"Two nuts, two water hoses, three fuel lines,one vacume line, and one ele. connection. the whole unit will slide out the low port front side.
the two nuts are at port motor mount.9/16
the two water hoses run from front to rear,it is usually easyest to take them off at the other end(rear cooler and T-stat housing)
the fuel lines are also best to disconnect from other end(two at fuel sep. filter) the other at fuel rail,(rear fuel line)
DO NOT KINK THESE FUEL LINES. if you do they will be damaged and will restrict fuel. they also cost around a hundred each.
the power connector is a snap and don't forget to disconnect the small vacume line(near power connector.
slide the whole "unit" out along the stringer to the front.
reverse to install."

 

[toy4two]

Reinstall tomorrow and retest

 

[toy4two]

I looked at my Quicksilver fuel pressure regulator which says Made in Japan and in looking up the OEM stamp, I found that it’s sold for the 1999 Honda Civic LX M/T 1.6L it’s rated 38-47 psi. I haven’t confirmed it’s identical but sure looks similar may have to unscrew one side of it. Only the original Honda part has the removable section to unscrew and fit the Mercruiser fuel line the aftermarket ones are welded shut. Not confirmed but worth researching more.

 

[alldodge]

Boats put all of us feeling like a pretzel one time or another

 

[toy4two]

Well bloody and bruised new HP pump and FPR installed. Engine idles very rough now. I made a video showing fuel pressure. Also on the FPR the vacuum tube seemed pretty loose but didn’t slip off, there was a green plastic washer on it that I removed but kept.

https://youtu.be/9U3dlvA5weg

 

[alldodge]

With showing almost 60 psi the regulator installed is not the right one, the screen between reg and cool fuel tube (real small screen) is clogged, or there is a restriction from the regulator back to the filter canister.

Its running rough because you have to mush fuel going in due to increased pressure

 

[toy4two]

I have the package the new Quicksilver FPR came in showing this part number: 861126A1

I put the new screen on that came with the FPR. I am still not sure how to use the green plastic piece on the new FPR with the vacuum tube or it really can be discarded, not that important as it isn't the issue.

All I can think is I some how installed the 2 fuel lines incorrectly either at the fuel water seperator, which would be difficult as I thought they were different sizes and only go on one way. I'm thinking there has to be a installation error as I doubt a new FPR or HP fuel pump could be bad.

 

[alldodge]

The HP fuel pump can produce 60 psi pressure, the regulator is what keeps it from doing that. The reg should open and send excess back to the filter.

Don't see an issue with the vacuum or the green thing, and can be tossed

 

[toy4two]

16740P2EA01 is the part number for any brave soul wanting to try the oem fpr through Honda and save the 50% Mercury marku.p.

 

[toy4two]

Im gong to try to get back to the boat and look for a kinked fuel return line under the engine going to the fuel water seperator