High Fuel Pressure 2008 MerCruiser 350 Horizon MPI

[kib1702]

Hi.
Does anybody know what is correct fuel pressure on 2008 MerCruiser 350 MPI Horizon.S/N 0W695578
Had low pressure on port side engine. Replaced fuel pumps, fuel filters and fuel pressure regulators on both engines.
Took the boat out and it has no power. Both engines will not go above 4200 RPM and max speed is 20-22 knots.
Checked the fuel pressure on the rail and it?s showing 80-100 PSI.
Can this be the cause of no power?
Some treads here recommended to check the return line for restriction, but there is no return line on both engines. My guess is that fuel pressure regulated inside of fuel module. Took both of them out and they are ok.
Any ideas?

Thank you for your help

2008 SeaRay 310 Sundancer
Twin 350 Horizon MPI Mercruisers
V-Drive

 

[alldodge]

Hi.
Does anybody know what is correct fuel pressure on 2008 MerCruiser 350 MPI Horizon.S/N 0W695578
Had low pressure on port side engine. Replaced fuel pumps, fuel filters and fuel pressure regulators on both engines.
Took the boat out and it has no power. Both engines will not go above 4200 RPM and max speed is 20-22 knots.
Checked the fuel pressure on the rail and it?s showing 80-100 PSI.
Can this be the cause of no power?
Some treads here recommended to check the return line for restriction, but there is no return line on both engines. My guess is that fuel pressure regulated inside of fuel module. Took both of them out and they are ok.
Any ideas?

Thank you for your help

2008 SeaRay 310 Sundancer
Twin 350 Horizon MPI Mercruisers
V-Drive

Howdy

With reading 80 to 100 psi you have a restriction and you more then likely damaged your regulators. Pressure should be 43PSI at 1800 rpm.

Has the engine been scanned for codes?

You have a digit off on your serial number it comes back as literature

 

[kib1702]

Yes it was scanned, no codes.
As for restrictions there are no return lines from the fuel rail.
The pressure was 85-100 at idle and 65 at 2000rpm

 

[alldodge]

The return line goes back to the filter from the regulator

 

[kib1702]

Thank you for your help i will check the restriction and pressure regulator.
Also i am attaching the pictures of S/N for both engines

 

[kib1702]

Hi again.
Turns out high pressure was caused by faulty fuel pressure regulators. Replaced all four (just in case) and pressure is 40-45 on both engines.
However there is still lack of power. The RPMs on both engines will not go above 4500 and max speed on water was 27 knots. Checked spark plugs and injectors, they appear to be ok. Both engines have about 350 hours.
Any ideas?

 

[thumpar]

4500 seems close to the range they should run. It may be a tad low but could be a dirty hull causing the issue.

 

[alldodge]

Hi again.
Turns out high pressure was caused by faulty fuel pressure regulators. Replaced all four (just in case) and pressure is 40-45 on both engines.
However there is still lack of power. The RPMs on both engines will not go above 4500 and max speed on water was 27 knots. Checked spark plugs and injectors, they appear to be ok. Both engines have about 350 hours.
Any ideas?

With inboards your WOT should be 4400-4800 rpm so your close. How long have you had the boat and has the performance been better?

 

[kib1702]

I have this boat since 2012 and it was going up to 4900 RPM and about 30-32 knots

 

[alldodge]

With your previous high pressure issue the engines were get way to much fuel. This could cause possibility cause other issues such as soot on plugs causing them not to fire correctly, washed out cylinders which can score the walls, even damage to injectors on the outside.

Suggest taking a look at the plugs and see if they need replacing. A compression test would also be in order.

Sure was weird to have both regulators go out at the same time

 

[skippy2235]

4900 RPM is a bit high, I would not want my engine that high, After you find out reason for losing power, I would get a bigger prop. Get those RPM down 500.
4500 should be max, no one wants to damage an engine if you are not racing. To much money just for an extra 5 mph.

Hope you have no engine damage now,
I agree an Compression check, and full tune up on ignition system.
Trust me I learned the hard way, Big MONEY and 2 engines later.
Find the max and stay 700 RPM away from it, I do not run my engine over 4000.

 

[kib1702]

Thank you for your help. I will change plugs and check compression and injectors..........
Will keep you posted...................

 

[kib1702]

Hi there.
Took boat out for a spin and starboard engine died. Went back to the marina on one engine, let it cool off and it did start again. Checked pressure it was ok. Connectors and wires on both fuel pumps were very hot. All problems started after replacement of all four fuel pumps and all four fuel pressure regulators.All new parts were aftermarket Sierra parts. At this point i have ordered brand new OEM (quick silver p/n 8M0047215) fuel modules. Will keep you posted...................

 

[skippy2235]

Are you sure you are not vapor locking. If you have HOT fuel pumps and HOT connectors. Some thing is strange.

 

[alldodge]

Connectors and wires on both fuel pumps were very hot.

The wires and connector should not be getting hot. The Pink/Green wire comes from the fuel pump relay and that comes from a 20amp fuse wire by the same color. Has batteries or other wires been removed/replaced or changed nearby. Reason for the question is if the circuit is loosing ground then there can be heat generated

 

[kib1702]

Are you sure you are not vapor locking. If you have HOT fuel pumps and HOT connectors. Some thing is strange.

What is vapor locking?

 

[alldodge]

What is vapor locking?

Vapor lock happens when the engine is hot, the engine is shut off and the fuel lines heat soak and boil the gas. Vapor lock takes some time to happen, like when folks stop and take a dip, and relax for a while. Your engines are stopping while running, IMO this is not your issue

 

[kib1702]

The wires and connector should not be getting hot. The Pink/Green wire comes from the fuel pump relay and that comes from a 20amp fuse wire by the same color. Has batteries or other wires been removed/replaced or changed nearby. Reason for the question is if the circuit is loosing ground then there can be heat generated

Never touched any wiring on the boat. Will check all grounds. On the other hand all of this problems started after i changed all fuel pumps.
It all started with port side engine. It had low fuel pressure (20-23 PSI). The pressure on starboard engine was fine (40-45 psi). I decided to change all fuel pumps. Along with pumps i replaced the fuel pressure regulators on the both fuel modules. Took boat out and it wouldn't go above 20 knots at 3900 RPM max.
Checked fuel pressure and it was 80-100 PSI on both engines. Replaced all 4 fuel pressure regulators (2 on fuel modules and 2 on fuel rails) Checked pressure it was 40-45 psi on idle. Test the boat it went up to 27 knots at 4500 rpm max. Yesterday the starboard engine start stalling.

Logically the problem has to be in new fuel pumps.

 

[alldodge]

Never touched any wiring on the boat. Will check all grounds.

Sorry my misunderstanding, what was getting hot?

 

[alldodge]

Never touched any wiring on the boat. Will check all grounds.

Sorry my misunderstanding, what was getting hot?