Loss of power

[mhawkins]

Hi Everyone. Im new to this site but have had my LSV 247 (8.1 Indmar engine) since new in 2007 and love it. No problems at all...till now. I have had a very apparent power loss recently...not as much torque on the low end and cant get more than 3800 rpm on the top end when on the water. Boat usually has great torque and rpms on the water will run up to 5000 real easy. When not in gear the engine will spin up to 5000 + real quick. Im not a real mechanic but I find no problem at all with the engine. Almost feels like the cruise control is on, or the balast is full of water, or the wedge is down...none of which are the case. 

I did have another issue recently but seems unrelated. The engine overheated several times on a trip to lake powell. Turns out I sucked up some debris on the lake and plugged up some lines. I was able to clear the lines and transmission cooler and replace the impeller (yes even tho im no expert I do know just enough to carry a spare impeller in the boat). Boat ran cool after that but power loss problem began. I took it to my mechanic when I got home (not a Malibu dealer)..he checked out the impeller, and the engine and could not find anything wrong. Boat still runs like a dog. Need some help. Any suggestions or ideas? 

[JeffK]

When was the last time you did a general tuneup?  I would start there based on the age of the boat. Cap, rotor, plugs wires. If you are pulling the plugs, I'd also do a quick compression test to rule anything out. 

[mhawkins]

yes, yes and yes. All good suggestions and we did that first. Still scratching my head. Wondering how overheating might impact the power so much without a cracked head, etc. Or maybe not related to overheat at all. 

[JeffK]

Replaced every item suggested?  Wires can get brittle if they get too hot. Excessive heat can mangle a cap or rotor too.  May or may not be related, but worth a shot. When was the last time you replaced the fuel filter?  I haven't worked on the 8.1 in years, but it was pretty bulletproof as I recall. 

Where are you located?

Edited August 14, 2017 by JeffK

[csleaver]

It might be a good idea to do a compression test and change the plugs, if that wasn't done already.  Look for any spark plug wire damage that may have occurred during the overheat while you are there.  Check the fuel pressure also.  I have seen an 8.1 seem to run fine with three clogged injectors, but it lacked top end power.  Hard to believe those motors could run with only five working cylinders until I saw it first-hand.

[Sparky450]

Does your boat have cats?

[JeffK]

Any update?  Resolved?