Hesitation at 2000 RPMs

[C-3]

I had around 2000 to 2500 RPMs the motor hesitates like it’s not getting enough fuel. Changed all ignition parts including cab Rota coil wires new plugs. I am now in the process of changing in-line filter water separator fuel filter and low pressure fuel pump question this is a fuel injected engine. Why do we have a low pressure fuel pump in it from the factory, 861155-4
Is there another high pressure filter down the line?
What is a good replacement source for the fuel pump - how do I test this 20year old pump?

 

[Scott Danforth]

I had around 2000 to 2500 RPMs the motor hesitates like it’s not getting enough fuel. Changed all ignition parts including cab Rota coil wires new plugs. I am now in the process of changing in-line filter water separator fuel filter and low pressure fuel pump question this is a fuel injected engine. Why do we have a low pressure fuel pump in it from the factory, 861155-4
Is there another high pressure filter down the line?
What is a good replacement source for the fuel pump - how do I test this 20year old pump?

Low pressure pump moves fuel from tank to high pressure pump. Very common setup

Before spending money, make sure to trouble shoot the system. What fuel pressure are you getting

Buy either a Mercruiser pump or a Carter/airtex (OEM pump)

Do not buy chineseum knockoffs from amazon

 

[C-3]

Low pressure pump moves fuel from tank to high pressure pump. Very common setup

Before spending money, make sure to trouble shoot the system. What fuel pressure are you getting

Buy either a Mercruiser pump or a Carter/airtex (OEM pump)

Do not buy chineseum knockoffs from amazon

Will an automotive pressure gauge work on the fuel manifold Schrader valve?
Where is the hi pressure pump located?

 

[C-3]

Will an automotive pressure gauge work on the fuel manifold Schrader valve?
Where is the hi pressure pump located?

 

[alldodge]

Will an automotive pressure gauge work on the fuel manifold Schrader valve?
Where is the hi pressure pump located?

Yes, connect to fuel rail schrader valve

 

[C-3]

Yes, connect to fuel rail schrader valve

I attached a pressure regulator to the Schrader valve on the fuel manifold and it’s reading 32 to 34 psi at all RPMs. I still have the hesitation between 1520 500 RPMs and pinging at higher RPMs.

 

[C-3]

I attached a pressure regulator to the Schrader valve on the fuel manifold and it’s reading 32 to 34 psi at all RPMs. I still have the hesitation between 1520 500 RPMs and pinging at higher RPMs. I changed the fuel water, separator filter and the in-line strainer filter and installed a new low pressure fuel pump with all new lines. This did not seem to help.

 

[alldodge]

With it pinging need to check timing. I would post how to check but don't have my laptop. Search HSV timing and should be able to find

 

[Scott Danforth]

I attached a pressure regulator to the Schrader valve on the fuel manifold and it’s reading 32 to 34 psi at all RPMs. I still have the hesitation between 1520 500 RPMs and pinging at higher RPMs.

Your pressure is low. I believe that MPI should be 43

 

[QBhoy]

Hi. Are you seeing this when in gear and under way on the water ? Or you mean it’s stumbling at 2000/2500 when you rev her out of gear in neutral ? Some mpi of an age won’t let you rev past 2000/2500 in neutral. It will limit the rpms. Some DTS versions certainly won’t allow you to rev past this sort of rpms at all in any state, if the outdrive is tilted up beyond a certain angle of trim either.

 

[C-3]

Hi. Are you seeing this when in gear and under way on the water ? Or you mean it’s stumbling at 2000/2500 when you rev her out of gear in neutral ? Some mpi of an age won’t let you rev past 2000/2500 in neutral. It will limit the rpms. Some DTS versions certainly won’t allow you to rev past this sort of rpms at all in any state, if the outdrive is tilted up beyond a certain angle of trim either.

Only feel the hesitation underpowered trying to plane at around 1500-2500 rpm - if I push past that range the engine feels and runs good until over 4000 rpm which then produces some detonation. If I putt putt under 1600 it also runs good without hesitation.
I’ve owned this boat for 20 years this problem started 5 years ago. I’ve been to multiple repair people which changed everything once or twice to no avail. I recently changed the in-filter, water separator, fuel lines and low pressure fuel pump. In addition I checked the fuel manifold pressure which is a steady 33 psi instead of the normal pressure of 43psi. My question is :
Is there a way other than changing them to test the fuel regulator and hi-pressure fuel pump or should I just change both of them. I’ve looked for them in the engine compartment which is not very accommodating I’m not able to locate their positions. Can you help me with locating them?
Many thanks!
C3

 

[alldodge]

The Reg can be benched tested with air pressure and a air Reg. Connect air to the bottom port and bring the pressure up slowly, it should open about 43

If Reg checks out its most likely the pump

To test pump connect gauge to output directly and when powered up pressure should go up to at least 60 psi once air is purged