1998 Crusader 350 XLi - RPM Fall-off until it dies after 45 minutes

[Fully_Vetted]

Good Day all,
Trying to track down a problem we've been having with our 350 Mariners engines.

Engines: 1998 Crusader 350 XLi's, Fuel Injected into the throttle body on top of engine, with ~ 550 hours on them. Boat has sat for about 18 months with last owner and accumulated less than 10 hours (in two main runs, and some small repositions).

Purchase Survey/Sea Trial
Both engines made 4200 RPM @ 22-23knt (Book says 4400 RPM is expected max, so this wasn't far off)
No issues observed on sea trial.
Since owning, the engines run a consistent 155-160 coolant temp and have never gone above that.

1st Run - Took Possession:
45 minutes into 1 hour motor to our home port and this:
1. Cruising at 3400 rpm, port motor starts slowing loosing RPM
2. after a few minutes, it can't maintain 300o RPM, regardless of throttle position
3. after about 4 minutes, it will barely idle and stalls/dies shortly after
4. Ran on starboard only until almost to our marina
5. right before entering marina, tried Port, and it cranked right up and ran fine for docking.

Assumptions - Old/bad fuel and "crud" in fuel tank clogging filters.
Actions - Cleaned some crud from both filters on both motors (disk and fuel/water separator) as well as filled tanks with new fuel (put just over 1/2 tank it each to bring them up to full).

2nd Run:
1. Ran to fill tanks (referenced above) right after refuel (20 min running to fuel dock) motors were still warm from run for fuel
2. Refueled, with about 80 gallons each side (twin 125 gallon tanks), engines off about 20 min’s
3. Departed at 3400-3600rpm cruise and after about 20 mins run, backed down to 2000 rpm
4. 45 min after departing fuel dock, port started loosing RPM slowly. Not abruptly, but slowly dropping what it could achieve or hold, increases in throttle did nothing to raise RPM.
5. It would make full RPM in neutral at first but not in gear, however after 2-3 minutes of troubleshooting, it wouldn’t even idle and died.
6. After nearly an hour idling on starboard, tried to restart port right before entering marina, and it cranked and ran fine

Assumptions – electric fuel pump on port was getting hot after a period of running and breaking down/failing. Let it cool off and it would work again.
Action – replaced both port and starboard electric fuel pumps.

3rd Run:
1. Short run for pump out. Ran fine, both engines made 3400-3600 no issue with throttles matched. 10 min run each direction.

4th Run:
1. Starboard would not make more than 3200 RPM, but required ¾ or just over ¾ throttle to make that, where as port was needing just under ½ throttle for that same RPM.
2. With engine RPM matched, starboard would not do more than 3200, but I could “Drag” starboard by pushing port up to 3600-3800 and get starboard to come up to 3400-3600, by running port harder
3. Ran that way for 1 hour before anchoring at our spot for the day.
4. Dove the bottom to look for anything “hanging up” starboard prop, but bottom and prop were clean.
5. This was the first time starboard had not acted correctly
6. Sat on anchor for 5 hours (engines fully cooled down)
7. Return run 1 hour home, same observations for starboard, and port ran fine.
8. Looked like starboard was burning more than port

5th Run:
1. Initial out of marina (engines barely up to coolant temp of 140), Starboard made about 3600, but after 5-10 min, would only make 3200 unless I “drug” it with higher port RPM.
2. 50 min – 1 hour run to anchor spot, ran about 3400ish on port, starboard stabilized around 3200 max, but still was ¾ throttle or more to get that RPM.
3. Return run 1 hour, same behavior.
4. Observed that starboard was clearly burning more fuel than port, close to ¼ tank difference now

6th Run:
1. Out of marine with cool engines (just passing 140ish coolant), port made 4800 RPM and likely would have made 5000 had I kept pushing (past its 4400 rated max continuous). Starboard made about 4300. Port was 4800 with throttle left, starboard was 4300 wide open.
2. Backed off to 3600 on both as was trying to make time and they were running good.
3. After about 10 minuets, starboard could no longer hold 3600 and was back down to 3200-3400 if I kept port pushed harder.
4. Ran port harder to make better time, approx. 45 min run.
5. Forgot and left battery charger on with genset running and engines running.
6. Anchored for less than 2 hours, with genset running, engines wouldn’t have fully cooled down after that time
7. Departed to new spot, but after about 20 min of running with port around 3400, noted that we felt like we were loosing power
8. Within a couple minutes, port started loosing RPM slowly, and over the course of about 3-4 minutes, port slowly decreased RPM regardless of increases in throttle and died.
9. Limped in on one motor, about 45 minutes, with port off
10. Before hitting marina, tried port after it had sat and cooled down, and it cranked right up.

Suspicion – fuel filters clogged or something other than the fuel pump, something ignition related or fueling injection related.
Action – Cleaned all four fuel filters for third time, nothing notable removed that would have caused issue.

7th Run – Immediately following 6th after fuel filters cleaned.
1. Motors still warm, left out, planned to maintain 3200 on both
2. Went to fuel dock – 20 min away, fueled up to ¾ tank on each side
a. Port took 35 Gallons
b. Starboard took 54 gallons
c. In approx. 8 hours of running, Starboard burned roughly 20 gallons more than port, and genset was only ever pulling from port fuel tank.
3. Motored one hour at 3200 with no issues, except Starboard still required ¾+ throttle to make 3200
4. Anchored for about 4 hours with genset running
5. Motored one hour back at 3200 with no issues, other than throttle split

Assumptions – Fuel pumps were likely not the cause of Port motor issue. It seems “something” on the motor is getting “hot” or breaking down and failing after about 20-40 minutes of running if the RPM is up around 3600+, but it doesn’t seem to happen if the RPM is left around 3200. 3200 is not ideal as it is just barely at planning speed so we are about as inefficient as it gets at that RPM.

Spark arresters on each motor were cleaned right after taking possession. Fuel is nearly all fresh new fuel and filters are clean and good. Motors never overheat. Unlikely it is fuel related or fuel pump related. Looking now at Injection at Electrical

Going forward –
Port - Injectors starting to fail? Port motor is still experiencing the RPM loss and failing, but we seem to have isolated it to possibly load or RPM related as opposed to just pure time related. The throttle body or injectors getting to end of life? The distributor and internal ignition is all likely original. Are both fuel nozzles in the intake spraying? Engines electronic fuel injection computer failing or getting hot and failing?

Starboard – Motor has seemed to run fine until after 3rd run. On 4th run, it wouldn’t make RPM and hasn’t since. It did seem to be burning a little more fuel prior to the RPM issue being observed but since then, I’ve confirmed its burning about 37% more fuel than port. I believe that I’m fueling correctly based on the throttle position, ie, its burning like I am running it at nearly wide open throttle, which is where the throttle is, but its preforming poorly as if I’m running at less than 50% throttle.

Any thoughts and directions would be greatly appreciated. Apologize for the book, but trying to summarize what all I’ve seen, in order, and detailed, as each time it seems to have been slightly different.

[g36]

I can tell you it doesn't take alot to clog the oberg (round disk ufo filter) and this can be cleaned. However none of the rest of the filters can really be cleaned. Each inline is filtering smaller and smaller particles. It would be my thought to replace the others and run it again. The symptoms too I have experienced and filter replacement took care of it.

[bud37]

Good on you for posting such a detailed account of the goings on and actions. The one thing that comes to mind after reading this is fuel starvation......have you cleaned the anti siphon valve on the top of the tank.....first.

You mention filters in the plural for each engine....can you explain further...is there only the one replaceable filter on the engine or have others been added.

[Viper]

Ya could be fuel delivery, the anti-siphon valves are suspect as bud mentioned, injectors, tank pick up issue, also make sure the tank is venting properly, try running with the deck fill caps open and run her in case there's a venting issue. If you're careful about it, you can isolate the engines from the boat's fuel delivery system by running the engines on portable fuel tanks. If they run great, the problem is not at the engine. If they run the same, you can eliminate the boat side.

Don't rule out an ignition system issue. If the parts look original, replace them so you can eliminate the ignition system as a possibility.

[mjk1040]

I'm thinking fuel filters, especially the orberg pancake filters, someone said they are so fine of a mesh that they would stop water from going through. That fine rusty dust in an orberg will starve fuel flow.

[km1125]

First, a couple thoughts one some things you wrote:

RE "Out of marine with cool engines (just passing 140ish coolant), port made 4800 RPM and likely would have made 5000 had I kept pushing (past its 4400 rated max continuous)."

Don't make that a habit... that's very abusive to engines if you want a long life out of them.

RE: "Forgot and left battery charger on with genset running and engines running."

That should not be a problem at all. Are you in the habit of turning it off? IMO that would be a bad habit because there's the chance that you might forget to turn it back on.

Agree with the earlier comments about the anti-siphon filter and the tank vents. Electric fuel pumps don't have a lot of "suck" so any unreasonable restriction on the input side will cause them to quite pumping. I'd check those because they don't cost you anything and both need periodic maintenance anyways, so it's not any wasted effort.

Also, as Bud alluded to, are you SURE there's not another filter right on the engine? Many injected engines have a fine filter AFTER the fuel pump and located right on the engine somewhere.

[g36]

I also have xli engines there definitely is a fuel filter at the throttle body it is like this...https://marinepartssource.com/crusader- ... 23250.html

[bud37]

I like vipers idea to run on a portable tank, that would eliminate all sorts fairly quickly.......

Of course if it takes a while running on plane to create the problem you may need a couple tanks.

[Viper]

Source of the post ...RE "Out of marine with cool engines (just passing 140ish coolant), port made 4800 RPM and likely would have made 5000 had I kept pushing (past its 4400 rated max continuous)."

Don't make that a habit... that's very abusive to engines if you want a long life out of them.
....

Agreed. Also, if you're managing that rpm in gear, you're propped wrong and can damage the engine.

[chpsk8]

Sounds similar to my issue last year.
Replaced the fuel pump on the motor, couldn’t find a ufo shaped filter near the throttlebody because someone replaced it with a more traditional metal inline filter. Replaced that one also. Also change water separators a couple times. Prime suspect was bad fuel which clogged filters and burned out the fuel pump.
I also have two fuel pumps per motor. One pony pump get it from the tank to the motor where the main pump moves it to the throttlebody.
Your issue sure sounds like fuel that is for sure. Lots of good advice here to get you down the path.