Low RPM, Slowly decreasing above 2k

[Eddie B]

Hey folks. Out last night and my 2003 240DA (5.0 MPI bravo) failed to get me home. I ran 30min to diner. Got back on. Motored out of the harbor and came up on plane. Within 5mins I was loosing RPMs. From 3200 to 3100 to 3000 came off plane. Shut the boat down restarted and tried again. Same thing. I tried a few more times. She started topping out at 2700 and I decided to turn around and go back to the restaurant. Motored 20min below 2k back to the dock without issue. Got a tow home. Boat seems to rev in neutral up to 4/5k no problem. Really no clue what it could be. Hope it is not a major out drive problem. I did take on 3/4 a tank of gas before leaving for dinner last night. But since she revs in neutral not sure it’s a fuel problem. Hoping for some guidance here before I get taken for another 5k this season :-(

 

[Eddie B]

Worth noting I’m not just loosing rpms but applying full throttle has not effect. Will not climb before the steadily decreasing limit.

 

[Eddie B]

Also not bogging. Sorry. Can’t stop thinking about it.

 

[Espos4]

Revving in neutral doesn’t prove much. There is no load on the engine so it can easily rev to a high rpm even with low fuel pressure or reduced volume.

Give us some maintenance history.
Last tuneup? Plugs,wires, filters etc.
Engine hours?
Engine temperature when this occurred

 

[scoflaw]

Tune up and check your fuel pressure for starts.

 

[Eddie B]

You guys are awesome. Bought the boat in April. So history is limited. Had it gone through and had a starter issue (last 5k I was talking about) which was fixed. New water pressure sensor, zincs, trim solenoid this spring. Oil was changed during winterization. Not sure the last tune up, or when filters where cleaned. Was planning on giving her an oil change this week as oil level was high (likely cause the prior owner added while test driving as there was an ignition issue and he thought it might be oil pressure related).

temp was 170. Oil pressure was around 40- 50. No alarms. Not bogging.

I think I can manage a tune up and filter cleaning/ replacement but I don’t have a scan tool. It would be great if I can check some things before calling in the only mechanic here in Stamford who does not like me.

Apx 265 hours on the engine. I say apx because new gauges were installed at 200 hours per survey don’t in 2020. Currently reading 65 hours.

 

[Espos4]

With limited history, you need to set a base line.

Full tune up with plugs, wires, fuel filter(s) and I’d inspect the manifolds and risers as well.

A compression test for baseline info would be good info to have.

 

[scoflaw]

You don't need a scanner to check fuel pressure. Go to Autozone, or Advanced Auto and borrow the test kit, no charge.

 

[Eddie B]

K. I am going to check the filters. Orr but the service manual for my engines fuel flow diagram does not match what I am seeing. And apparently I have the “cold fuel” setup?

 

[Eddie B]

Added two Picts of the manual and the engine. That small silver thing to the left of the skinner valve… is that and in-line filter?

 

[Eddie B]

Ok. So I just started the engine and see water squirting out from what seems to be a screw or fitting of some sort just right of center. Picts below. First time I was able to run her and it was dark last night.

 

[Wanderer 290]

That appears to be a npt pipe plug on the intake coolant crossover.
Is the vessel a salt water vessel? It may have rusted inside out.
Getting the plug out will be challenging.. Drill and have a npt tap on hand.

That may or may not be the source of your low rpm problem but definitely needs repair. The excess water may have faulted a sensor causing the low rpm condition.

 

[Nater Potater]

Added two Picts of the manual and the engine. That small silver thing to the left of the skinner valve… is that and in-line filter?

Yep, fuel filter, but it looks like something that was added later, and not the water-separating type. That would be my second red flag. The first? You mentioned recently taking on 3/4 tank of fuel; was that from a known good source? You could try pulling that filter, being careful to catch any liquids that come out while removing it. Check for any water in the captured liquid.
And, as @Wanderer 290 mentioned, that looks to be a rotted plug. You might be able to get after it with a large EZ-Out, but, if it's rusted that bad, it might be in need of greater efforts (pull manifold, machine out plug, clean up threads). Break Out Another Thousand!

 

[Eddie B]

Thanks guys! Yes. It is a salt water boat. All we have here is salt water on the east coast ;-). I didn’t pull the filters yet. I found a retired mechanic who does part time dockside repairs (friend of a neighbor). He came down. Took a look. Had me wash down the engine with salt off from west marine and will be back tomorrow with a new plug, test my engine alarm (as I had no alarm, and no beep at start up) and use a scan tool on the engine. Hopefully things go smoothly. Will keep you updated and appreciate all the support.

 

[Fill Ess]

Wasn't sure if you were referring to this or not, but that's your inline fuel filter. I can't tell from the top view but do you have the water separating one too? It looks like an oil filter and would be below the alternator.

 

[Eddie B]

Wasn't sure if you were referring to this or not, but that's your inline fuel filter. I can't tell from the top view but do you have the water separating one too? It looks like an oil filter and would be below the alternator.

View attachment 108891

I do. It’s to the bottom starboard of the engine

 

[Eddie B]

Anyone know what the part number is for that plug?

 

[Wanderer 290]

I believe it is a standard npt pipe plug available at most hardware stores. You may consider going with brass as a replacement.
Use Teflon tape with installation.

 

[scoflaw]

Don't get the ones that need an Allan wrench to remove, they can strip and the your screwed

 

[Eddie B]

Don't get the ones that need an Allan wrench to remove, they can strip and the your screwed

Lol. “You’ll be screwed”. I think I already am. Saltwater all over the motor. Is that salt off stuff from west marine any good? Mechanic said to use simple green.