300XS won't deliver full power; returns no codes/faults. Can barely get 4500 RPMS.

[Philster]

Background: Engine ran great; into max RPM range and boat ran 65-70. Came off plane from doing 60... cruised a no-wake zone, then went to accel and she was weak. No bog. No miss. Nothing but 'weak'. Ran to 4000 RPM and not much more. Merc tech got 4500 RPM and that is it.

Other info:

Hours: 13 (yes, 13)

Hole shot: Barely. Barely enough power to plane.

Mid range: Soft, anemic

Upper RPM: Can't get there. 4000... maybe 4500.

67-70 MPH boat reduced to wimp begging for 45... 50 with luck.

Codes or Faults: None.

We're going to drill down with these things one by one (water test after each one), but please add to this list or re-arrange it:

Plugs: replace
Coils: replace
Fuel: run off fresh portable test tank

Plugs look good. However, I've heard it recommended they be replaced anyway. One looks ever so slightly different than the others. Barely.

No water in filter.

Any ideas/suggestions?

[hydrostream1]

Did you check fuel and air pressures?if you have either one low it will run like a three legged dog.

[Philster]

We'll put it on the list.

Aren't the coils the first thing to check for a 300XS?

[Frank Molé]

did you check compression ??

[stokernick]

still in breakin mode??

[Philster]

Break in mode cleared 7 hours ago.

Compression? Well... I guess a new opti could have burned a hole in a piston... but shouldn't we pursue most likely scenarios first?

So, I was sort of hoping for a list of things to check first on a 300XS.

[obrien]

Since it is very easy to do a compression test, why not do it. You may need to find a dealer or mechanic that has the cds tool to diagnose this problem. If the engine is new it should be under warranty so why not have a dealer do the work, or is the engine out of warranty?

[87starflite]

pull the heads... have heard of others having similar problems and the sleeves had spun inside the cylinders blocking off the ports. very hard to diagnose unless you open up and take a look. Compression will most likely come up good

[iammarcuse]

If the engine is new it should be under warranty so why not have a dealer do the work, or is the engine out of warranty?

Ditto
You shouldn't even be touching it. Let the dealer figure it out and don't let him tell you that everything checks out. Water test says otherwise.

[FUN4ME]

Plugs look good. However, I've heard it recommended they be replaced anyway. One looks ever so slightly different than the others. Barely.


Any ideas/suggestions?

Sounds just like what I went through.
Mine turned out to be a bad coil, replaced it and all was good again for a while....
Lost 3 more coils and took out the ECU.
My advice have ALL of the coils replaced if you find one bad one.
good luck

[Philster]

It is warranty work by a Merc tech, but I say 'we' because his brain ain't the only one in the game. "We" are on it and using advice offered here!

Thanks!

[hydrostream1]

Yes,I agree if under warranty ,let the dealer diagnos it.

[merctech5591]

The opti motor will barely plane off even on 5 cyl. First thing I would do is odiously a cyl drop test and isolate the problem to a specific cyl. Next would be a fuel/air test and also test the return fuel pressure at the vst( make sure it is checked under load). If all checked out ok I would go thru compression . You should see 140-145 psi per cyl.once you have the plugs out I use a snap on bore scope and look at the sleeve allinment with the block . It is doable with out removing a head and waisting 2hrs of disassembly and reassembly. I have not seen any sleeves turn on a 300xs but have seen a few on the 250's. And these were all very low hr motors .10-12 hrs.

[merctech5591]

Forgot to mention. I had a motor a few months ago give me fits. Similar issues as your describing. This motor had ingested the yellow flywheel plug that covers the nut. It was stuck in #6 Rees block partially opening one Reed, and blocking the flow of air to that cyl.check your flywheel and pull the throttle body, you can stick your whole arm in there and check .

[Philster]

Tech going over everything right now and Merc HQ has worked with him and suggested based on what has been tested it is likely not electronic/electrical at this point. They did mention a spun sleeve as a possibility.