Help- 6.0l has lost it's spunk

[Bdecker]

Our 2011 Malibu LXI seems to have lost a little this season. It is still pretty good, but some passes it just seems a little slower out of the hole. Runs nice and smooth at speed, but with our short site the lack of holeshot is becoming noticeable- just did plugs, wires, etc... Any other ideas? It's a 6.0l with 650 +/- hours. Running 89-93 octane

[MISkier]

Do a compression test. What kind of water are you running the boat in? Is it clear and relatively particulate free or is it muddy/milky with clay or other cloudiness?

[oldjeep]

I'd do a compression check on it and also only use the 91+ octane fuel that indmar recommends for that engine. Also might be worth monitoring the fuel pressure in case the pump is getting weak.

[mlange]

91 octane??? The 6.0 is an L96 so it should only require 89 octane, right? It's the LS3 and LSA that require 91 octane per the 2012 Indmar manual.

 

Mike

[oldjeep]

2011 manual says l96 gets 91 octane. This is from the indmar manual.

 

Fuel– Your engine was designed and certified to operate on the unleaded fuels listed below. Fuel ratings must be based on the (R+M)/2 method and meet the specifications ASTM D4814 in the US. These fuels need no additives for proper operation.

•Malibu LS3, L96, LS7, MasterCraft LY6, L96 and Indmar LS2 engines 91 octane

 

•All other Indmar, Malibu or MasterCraft Engines 89 octane

[Bdecker]

Pond is a little weedy but not terribly milky. Just called dealer and it turns out they didn't do cap/rotor in their "tune-up". Thinking I'll start there and fuel filter, then move to compression test. We've been running 93 all summer, so I doubt it is fuel- manual for this engine (L96) says 89- the "hammerhead" gets 91

[Bdecker]

Pond is a little weedy but not terribly milky. Just called dealer and it turns out they didn't do cap/rotor in their "tune-up". Thinking I'll start there and fuel filter, then move yo compression test. We've been running 93 all summer, so I doubt it is fuel- manual for this engine (L96) says 89- the "hammerhead" gets 91

[oldjeep]

Sounds like a good place to start. Hard to believe they did plugs and wires without cap and rotor.

 

As for the octane, sounds like you are fine, but what manual for a 2011 are you looking at? This is the 2011 indmar manual

https://www.bakesonline.com/images/MediaLibrary/Indmar_2011manual.pdf

[DW]

@Bdecker: you might also want to get the injectors cleaned and change all the fuel filters. If you are doing a compression test, I would also add a leak down test with that, much more revealing than just a compression test. I would also run a timing light on it to verify it is correct. Cap and rotor corrosion is pretty common in marine environment, with 650 hours that should have been part of the process unless they checked it and determined no change was needed.

[MISkier]

The reason I asked about water clarity is that mud, clay, etc. can get trapped in the channels in the block. Then, when the engine cools, it can harden like concrete. Eventually, this restricts water flow enough to overheat small portions of the block and melt a cylinder or two. This can cause a loss of power and require a rebuild.

[mlange]

@oldjeep They must have changed the octane requirements starting in 2012 then.

 

The 2012 manual states exactly what you posted, but that first bullet point only references the LSA and LS3.

 

 

[eleeski]

Check the easy stuff with the engine - tune up, fuel filters, compression test and a code check to make to make sure all the sensors are working right. I'd bet you are OK there but the cap and wires might help. This is pretty standard maintenance - even I do this.

 

I'd have a look at the prop. Props get dinged up and can lose fine tuning. This can take the edge off performance. I've had more boat performance issues due to bad props than engine problems.

 

Eric

 

ps Regarding fuel octane, my Cessna had more power running low octane car gas than the 100 octane avgas. Climb and speed were measurably better but the engine did run hotter. Makes sense as higher octane has a slower burn to prevent knock. Premium fuel has other advantages but it should not improve HP.

[thompjs]

Check fuel pressure too

[skiep]

This sounds silly but, check the flame arrestor/breather. It will rob power if dirty.

[DanE]

@eleeski Most engines today have knock sensors, so a lower octane can lower performance by forcing a lower spark advance. If you have that scenario a premium fuel can actually improve hp.

[skihart]

My Indmar 6.0l MC eats plugs for breakfast. I change them every year but run regular copper top's. I had the same symptoms as you, slower out of the hole a few miles off the top end. Changed the pugs out and bam, back to normal. I did a little research on MC team talk and a tech there gave my suggestions for the copper tops inseam of $$$ platinums. I change them every year but run regular copper top's. I have the LQ9 motor in my boat.

[thager]

Friend's Nautique with a PCM 6.0L was a dog! Changed plugs and same. Gap was wrong. Changed gap and was like a whole new boat!

[PUNKEE]

Our boat (mercruiser engine) and a friends Nautique recently lost a little power, both of them run in muddy (brown) fresh water, both had cylinder head valve seat issues. Valve seats had corroded, causing power loss on both boats.