Motor Stalls or Sputters In Gear

[Sheperd80]

Hi folks, new to me 2008 Pro XS 225, 370 hours.
Sn: 1B520053

https://youtube.com/shorts/MuFZOWm4ibo?feature=share

The boat idles, and runs great but when i put it in gear it occaisionally stalls, when i give it just a little gas (around 1000 rpm) it will surge or miss a little. Even after only brief fishing stops. After a few minutes of idling or putting around at low rpm it will generally stop. Water temps have been around 52.

However it wont do this at all when earmuffed in my driveway. Even after a cold start it idles great, no stalling or missing when in gear and rev'd to 1000 rpm.

Was all set to start inspecting fuel, air, spark systems but this has me thinking i should be looking at the lower unit if it only does this in the water.

Worth noting previous owner had left half tank of gas in the boat for 6 months. He pumped it out before selling to me. For kicks i replaced the fuel filter. No change.

Any input is appreciated, thanks.

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EDIT: Here's the current list of work performed to make this easier for those kind enough to read and help. Thank you all! I will keep this updated here.

WHAT IVE DONE SO FAR: (8/15/22)

-Replaced all fuel lines and primer bulb (they were decomposing)
-Replaced fuel filter
-Rebuilt pulse pump
-Replaced VST seals and tested fuel pumps
-Replaced shorted ignition coil and 20a fuse (fuse blew at idle)
-Replaced water-in-fuel sensor (it died on the water)
-Replaced spark plugs (existing were gapped incorrectly and lightly fouled)
-Replaced a weak coil, slight improvement (it failed a 7/16" spark test)
-Got a Full History Printout revealing a couple overheats, and an open circuit injector.
-Inspected and adjusted injector wire (wires were pulled too tight, no apparent damage)
-Replaced all remaining ignition coils
-Installed Vessel View Mobile
-Replaced impeller and water pump gaskets
-Changed lower unit oil (old oil was milky green)
-Replaced spark plug wires
-Sent in all injectors for testing and cleaning
-Testing found 4 bad direct injectors and 1 borderline fuel injector
-Replaced bad injectors.
-Replaced ignition coil wiring harness (found poor conitnuity on one wire)
-Test drove twice at <5k rpm. Idle issue SEEMS to be resolved.

[JOE54]

cheap test,replace pulse pump diaphram or complete pump and red top filter , possible worn or weak diaphrams in pulse pump also inspect lines and bulb for deteriorating/look in bottom of filter chamber for debri , if it dont fix it move on to more intailed tests of fuel system , dout gearcase is problem

[EuropeanAM]

Just a friendly reminder: If you would, please take a moment to review the Announcements at the top of the Forum, and be sure to provide the Required Info (serial number) when posting. Thanks!

Do you have a Smartcraft Instrument? Good idea to confirm that both banks of cylinders are coming up to at least 120 degrees F (AT IDLE). If one bank does not, it can cause the engine to act as you've described (and may become progressively worse as it eventually begins to foul plugs).

[Sheperd80]

Edited the OP to add the serial number, also looks like i chose the wrong forum, my apologies.

No i dont have a smartcraft, so no idea what temp the engine is reaching but i do let the engine idle for several minutes before accelerating. Sounds like id be wise to check my plugs for fouling?

Update: i removed the new fuel filter and found maybe a tablespoon or more of sediment in the bottom of that cavity.

[JOE54]

NOT AGAIN please see FAQ at top of page look at engine performance problems

[Sheperd80]

Im realizing what an incredible resource you guys have put together here. Youll have to forgive a newbie for not reading all the stickies and FAQs. Now i know.

Ill check my hose when i get home but its definitely grey. So that leads me back to your previous advice about the pulse pump as its in line before the filter and may be full of crud or damaged?

Thanks you guys are great! Sounds like i have a clear direction to get started atleast. Will update soon.

[JOE54]

clear as mud , only way that can get there is degraded fuel lines , follow directions in FAQ to a tee

[SilverFox579]

Ill check my hose when i get home but its definitely grey.

Grey alone isn't the discriminator. Grey Mercury fuel line grey with red lettering = bad, grey with blue lettering = good. Even the blue lettered fuel line should be replaced if suspect. As Joe indicated, be sure to follow the the advice in this topic skipping nothing - FUEL LINES AND PERFORMANCE PROBLEMS

JMHO, with an Optimax you really need an accurate way to monitor coolant temperature and pressure as they are the most critical parametes in ensuring long engine life. Visit the Smartcraft topic in the Sticky topics for options, the Vessel View mobile is an economical solution for protecting your engine.

[Sheperd80]

So i do have the grey hose with orange lettering and its falling apart inside. From tank to bulb is a black hose that looks good inside and rather difficult to replace so i may leave it. Planning to replace bulb, hose from bulb all the way to motor eliminating the plastic splice that someone did outside the cowling so i have a straight shot. And going to replace gaskets on the pulse pump.

After cleaning the debris out of the vst the motor is running a little rougher in gear so i fear i may have pushed some debris into a bad spot. I did this before reading the sticky. Hoping i dont have to remove and clean out the vst as well but seems inevitable at this point.

Looking into the various smartcraft options. VV mobile looks like the cheapest/easiest. It seems crazy to me that these boats dont all come with a temp gauge as its obviously critical to taking good care of the motor.

Thanks!

[JOE54]

when you rebuilt pulse pump did you use new OEM kit ????? do you see any fuel comming from vst vent fitting = no = you have another problem , should not efect idle quality

[Sheperd80]

when you rebuilt pulse pump did you use new OEM kit ????? do you see any fuel comming from vst vent fitting = no = you have another problem , should not efect idle quality

I havent rebuilt the pulse pump yet, i just removed debris from inside the fuel filter area. But after reading dons post it sounds like theres a potential for blocking an orifice inside that chamber if not careful when removing debris?

[EuropeanAM]

I havent rebuilt the pulse pump yet, i just removed debris from inside the fuel filter area. But after reading dons post it sounds like theres a potential for blocking an orifice inside that chamber if not careful when removing debris?

There's a VERY good reason that the post recommended (and linked) above states VERY clearly not to substitute items, not to do a piece now a piece later, and the reason is that you always end up chasing the same problem over and over.

ALL lines, bulb, pulse pump kit and fuel filter should be replaced AT THE SAME TIME. Failure to do so leaves room for debris being transported from one area to another, weakened or compromised fuel pump, restricted filter, lean running conditions, and potential for performance problems (or worse yet, engine failure).

[Sheperd80]

Hi don, i havent replaced anything yet except the fuel filter. And that was before reading through that entire faq. Finding the debris in that chamber is what led me to all this information. I hear what your saying, I should also replace the tank to bulb line at the same time i do everything else.

Should i also remove and clean the VST? As mentioned above, i removed the debris in the fuel filter cavity and after that my in-gear idle was noticeably worse (only when on the water, runs fine on ear-muffs). I plucked it out with tweezers and a paper towel but its possible i pushed it into something?

Thank you for any input and all the information youve provided here.

[EuropeanAM]

It's very likely that the filter did it's job and kept the "nasty" from entering the aft chamber. Clean all the way to the filter chamber- DON'T use any solvents (other than gasoline) in the chamber.

Fresh/clean filter, lube the o-rings with 2-4-C.

Most problems that might surface in the aft chamber are quite pronounced (and significantly more troublesome).

[Sheperd80]

Parts have been ordered.

Since we ran the boat yesterday i decided to pop out the fuel filter again and see if any more debris had piled up. There was a small amount so i tweezed it out, put it back together, threw on the earmuffs and fired it up. Motor started and died in about 5 seconds. Now it wont start at all...

Noticed a little bit of fuel on this fitting.

[JOE54]

important ,,,, metal clamped fitting is high press to rail no fuel should be present , tie wraped fitting is vst overflow would indictae flooding vst( possible debri in inlet fitting ) also no fuel should be present

[Sheperd80]

It was the metal clamped one going to fuel rail. Noticed a small amount of fuel there after trying to start the motor.

[Sheperd80]

Makes me wonder if theres not a blockage in that line causing it to leak at the fitting under pressure? Any advice? Not sure if i should replaces hoses and all that if i have another problem beyond the fuel filter.

[Sheperd80]

Discovered a blown 20a fuse designated to ecm/fuel pump/oil pump in the manual.

Replaced the fuse but havent tried turning the motor anymore based on other threads here.

Also pressed the schrader valve on the back of the vst and got only a dribble of fuel with bulb pumped firm.

Sounding like one of the pumps inside the vst is either clogged or dead?

[Sheperd80]

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