reduced RPM while riding

[SJRwake]

I have a 2000 Sunsetter VLX with the Monsoon 350ci EFI that has 400 hours on it. I just recently replaced the fuel pump as it was failing and replaced the fuel filter closest to the fuel take with a fuel water separator while I was at it. I did not replace the fuel filter between the fuel pump and the injectors, though I probably should. The boat runs great; however, every once in a while it will begin to sound like its stalling and the RPMs will drop for a short time and then all the sudden it will resume normal operation. Has anyone else had this issue? Could it be the fuel filter that I did not replace is just dirty? Could it be the injector rails themselves need to be opened and cleaned out? Could it be the tiny injector filters are clogged? I wouldn't imagine its the distributor since it only happens occasionally. I also don't think it's the spark plugs. I an sitting solid at 170-175PSI on all 8 cylinders. I also ONLY run this engine in fresh water and ONLY run it with 89 ETHANOL FREE marine gas. As I live on the river in FL it gets run at least once a week year round.  

[williemon]

Id be cautious with the fuel water seperator. If that was not there before, id take it out and put no finer that a 40 micron filter back in place. May not even need that much of a filter. Those fuel pumps dont pull fuel well and the seperator without using a second fuel pump that will feed it will introduce a resistance that may cause the main fuel pump to loose prime for a second. Something to think about. Also make sure your electrical connection is good.  

[SJRwake]

On 8/21/2018 at 9:09 PM, williemon said:

Id be cautious with the fuel water seperator. If that was not there before, id take it out and put no finer that a 40 micron filter back in place. May not even need that much of a filter. Those fuel pumps dont pull fuel well and the seperator without using a second fuel pump that will feed it will introduce a resistance that may cause the main fuel pump to loose prime for a second. Something to think about. Also make sure your electrical connection is good.  

I have never heard about that happening before but it really does make sense! Thank you so much for that advice, I will check into that next time I am out!

[formulaben]

True about adding the water separator...FWIW I added one in conjunction with the secondary fuel pump to stop the dreaded vapor lock.  Never had an issue since, and I certainly feel a lot better about the 10 micron fuel filter than the garbage that came OEM on the engine.  The cost of rebuilding/replacing fuel injectors is well worth the effort.

[SJRwake]

2 hours ago, formulaben said:

True about adding the water separator...FWIW I added one in conjunction with the secondary fuel pump to stop the dreaded vapor lock.  Never had an issue since, and I certainly feel a lot better about the 10 micron fuel filter than the garbage that came OEM on the engine.  The cost of rebuilding/replacing fuel injectors is well worth the effort.

man I dont know, adding another fuel pump is another $400 for the pump itself, where would you even put the second pump? as for the 10micron filter, are you talking about replacing the filter that goes into the injector rails? how much did it cost you for new fuel injectors?

[formulaben]

1 hour ago, SJRwake said:

man I dont know, adding another fuel pump is another $400 for the pump itself, where would you even put the second pump? as for the 10micron filter, are you talking about replacing the filter that goes into the injector rails? how much did it cost you for new fuel injectors?

It's not a primary fuel pump, but a 6-8psi secondary pump; around $85 not including hose clamps and barbs.  The kit that Bakes sell is over $400 but DIY is less than $120 for sure.  Depending on what you of model you have, it is all but necessary since Indmar installed the fuel pump directly to the engine block where it would heat soak and cause vapor lock.  Just do a search for vapor lock and see how many threads and instances there are.  If you're not prone to it, then count yourself lucky.

As for the 10 micron filter, it's intended to protect the injectors...any dirt gets in there, you will need new or overhauled injectors.  They're not cheap, so I consider the fuel filter upgrade preventive maintenance.

[SJRwake]

1 hour ago, formulaben said:

It's not a primary fuel pump, but a 6-8psi secondary pump; around $85 not including hose clamps and barbs.  The kit that Bakes sell is over $400 but DIY is less than $120 for sure.  Depending on what you of model you have, it is all but necessary since Indmar installed the fuel pump directly to the engine block where it would heat soak and cause vapor lock.  Just do a search for vapor lock and see how many threads and instances there are.  If you're not prone to it, then count yourself lucky.

As for the 10 micron filter, it's intended to protect the injectors...any dirt gets in there, you will need new or overhauled injectors.  They're not cheap, so I consider the fuel filter upgrade preventive maintenance.

Thanks for all this info. SO i did just recently replace the OEM fuel pump with the new conversion kit that indmar makes(since the OEMs are not longer produced. The new one was i believe $380 but I'm very marine engine savvy so its all free labor haha. I'm just a littler confused on where a secondary pump would go on the system? I'll do some research into vapor locks!

[formulaben]

Secondary goes anywhere upstream of the primary pump, e.g. between fuel tank and primary pump.  I tied the electrical into the same plug as the primary pump.  The vapor lock was caused when the primary pump would first turn on and would cavitate due to the hot housing and fuel, causing the vapor lock.  The secondary pump with its light pressure stops the cavitation and allows the primary pump to properly prime and product effective fuel pressure.  On the newer models they moved the fuel pump into the fuel tank where it stays relative cool, so it's not an issue.

[SJRwake]

4 minutes ago, formulaben said:

Secondary goes anywhere upstream of the primary pump, e.g. between fuel tank and primary pump.  I tied the electrical into the same plug as the primary pump.  The vapor lock was caused when the primary pump would first turn on and would cavitate due to the hot housing and fuel, causing the vapor lock.  The secondary pump with its light pressure stops the cavitation and allows the primary pump to properly prime and product effective fuel pressure.  On the newer models they moved the fuel pump into the fuel tank where it stays relative cool, so it's not an issue.

dang this is all really interesting, i mean i never would have thought of this happening. I was worried at first that the new pump i installed may have had issues or that the filter i left on there was clogged(though im sure it would be smart to replace it anyway). so is there a negative effect from having a fuel-water separator installed if you also have a secondary pump? I mean I already run with ethanol free fuel but I know that typically those filters are just that much more preventative from water moisture and dirt getting into the engine.

[williemon]

Some, mine included did not come with a filter just before the fuel rails. It went tank, filter, pump, fuel rail. Any particles coming off the fuel pump and rubber hose after it went right into injectors. Several of mine were. Clogged. When i did a diy secondary pump install, i also replaced all rubber hoses and had new hi pressure hose and crossovers made. I installed an 8 micron hi pressure filter after the fuel pump and before the fuel rails. 

[SJRwake]

2 minutes ago, williemon said:

Some, mine included did not come with a filter just before the fuel rails. It went tank, filter, pump, fuel rail. Any particles coming off the fuel pump and rubber hose after it went right into injectors. Several of mine were. Clogged. When i did a diy secondary pump install, i also replaced all rubber hoses and had new hi pressure hose and crossovers made. I installed an 8 micron hi pressure filter after the fuel pump and before the fuel rails. 

love it, looks like ill be adding a high grade micron filter before the rails and switching the one thats there out