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2008 4.3 MPI Losing power

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Buzzz

New member
My 2008 Mercruiser 4.3 MPI is losing power (rpm's)
I bought the boat last Monday and ran the boat up to 55 mph on the test drive. My first real trip was great but my RPM's started dropping. By the end of that trip I could only get 4000 max rpm's and about 40 mph. Today started out with a max of 4000 and by the end of the day I could only reach 3000 rpm's wide open and trimmed up. Now at lower rpm's, the engine seems to be surging in and out. Any ideas? The engine only has 100 hours and starts and idles perfectly.

More info...

Oil pressure 35-40 at idle and 45-50 wot
Engine temp never reads over 155
No alarms
Running only non ethanol fuel and one can of sea foam with fill up.
 
Last edited:
Chris,

Thanks so much for the info. I've been pulling my hair out trying to figure this out. Is this something I can do myself or something you recommend taking to the dealer? I'm pretty handy but I don't want to screw anything up.
 
Opps. I really need to get some glasses. Did not see the 4.3 on the heading. Never the less. You will need a fuel pressure gauge and some new fuel filters. You can get a gauge at sears.
 
I can put my hands on a fuel pressure gauge. I'll pick up new filters in the morning. What should I be looking for?
 
The 43 psi was running as fast as it will run at the moment. It will only get up to 3000 rpm's. Its like the engine is surging and won't go past 3000 rpm's.
 
Gotcha. Will do in the AM. I waited til dark and hooked the hose up in the yard. Looked for a possible plug wire sparking somewhere but didn't see anything. I did notice a sensor on the back of the engine leaking water out of the fitting with the hose hooked up. The water was cold so I'm assuming its a water temperature sensor or something. I'll pick one up tomorrow and get it replaced also.
 
I would at least pull the spark plugs to see how they are firing...you want to see a medium brown color on all 6.
 
Finally decided to have the boat scanned. No codes on the hose at the dealer. They tested it today on the water with the computer onboard. Still nothing. Now they are changing plugs and testing compression. A couple of the plugs were fouled a little. They also said they are going to pull the elbos and and see if the exhaust flappers are stuck. It makes sense if they were stuck or partially stuck it would be like a plugged up muffler. What do ya'll think?
 
Update......
Dealer called. After replacing the plugs, which needed replacing anyway, they put the boat back in the water. It ran fine for a couple minutes and started acting up again. One of the technicians climbed on the swim platform and watched the engine while the other went WOT. The water tube on the back of the engine that holds a sensor started spraying water right on the coil pack and the entire back of the engine. He took his shirt off and wrapped around the tube, putted around for a minute to let things dry. After things dried a little, the engine performed perfectly. I think the salt water may have damaged the oil pressure sensor because they were getting a low oil pressure alarm but the pressure was fine. I'm assuming the guy whom I bought the boat from didn't winterize and water froze in the tube and caused the crack.
 
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