Sorry for first post being a long one, scratching my head on this one.
Having some issues with my mercruiser bogging down lately. 2004 5.0 MCM. Never had anyissues before this season, boat has run really good for us for 7 years.
-Placed new plugs in (AC-MR43LTS) all eight cylinders at start of this season
-Changed engine and outboard oil
-Changed water fuel filter after letting it run for a few minutes
First time taking it out, runs fine at low rpm as well as 4000rpm. Got up on plane no issues, ran for about 45 mins at cruising speed then started bogging down. Motor would not let me go above 2500rpm or would start to choke/sputter (no back fire) Ran fine at lower rpm. Could even place it in neutral, and rev the motor above/up to 4000rpm but, bogs down under load. Limped it to our destination, turned the motor off and let it sit for a few hours and put a new water fuel filter in (2nd this season). Fired right up and ran normal all the way home, 4000rpm no issue. I chalked it up to first time out for the season maybe little to much water in full from sitting all winter.
Taken it out several times since then, had the same issue. Always on the way out, about 45 mins into operating temperature. Will sit, run fine home. This weekend I pulled the distributor cap and rotor button off. All 8 of the terminals were corroded over. I couldn't even get the rotor button to slide off the shaft. Had to carefully cut the button off. The shaft was completely rusted over. Cleaned it, back to new with some sand paper and inspected it for anything significant....nothing found. I inspected the plug wires but the inside of the boots looked fine so I choose not to replace them YET.
Go out yesterday, boat starts up fine. Did feel like it was a little sluggish getting on plane, almost like we had 20 people sitting in the rear (we didnt). Eventually get on plane, ran fine at 4000rpm. Make it out to the same damn spot on the river (must be cursed) and it starts having issues. Not the same as before, started sporadically backfiring only between 2500-400rpm (first time for this). Lower rpm fine, but didnt like high rpm and would bog down again like normal. Turned it off, let it sit for 20 mins while the kids swam. Ran fine the last 10 mins of our ride. Sat another 5 hours then ran completely fine all the way home at 4000rpm.
By no means am I a mechanic but i have a decent understanding of how things work. I was initially leaning towards still something in the fuel, sloshing around and getting picked up which is why it works after boat sits for a bit. Tempted to drain my tank rather than keep going through water filters. Next step, rebuild the carb and put the new plug wires i have on. Im not the first owner, so no idea if its been done before. Then replacing all the fuel lines is also on table, boat is 18yrs old The back firing is interesting as it just started AFTER i put the new distributor cap on. But its sporadic so i go back to fuel or carb issue i guess.
Thoughts? thank you in advance for your time
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Having some issues with my mercruiser bogging down lately. 2004 5.0 MCM. Never had anyissues before this season, boat has run really good for us for 7 years.
-Placed new plugs in (AC-MR43LTS) all eight cylinders at start of this season
-Changed engine and outboard oil
-Changed water fuel filter after letting it run for a few minutes
First time taking it out, runs fine at low rpm as well as 4000rpm. Got up on plane no issues, ran for about 45 mins at cruising speed then started bogging down. Motor would not let me go above 2500rpm or would start to choke/sputter (no back fire) Ran fine at lower rpm. Could even place it in neutral, and rev the motor above/up to 4000rpm but, bogs down under load. Limped it to our destination, turned the motor off and let it sit for a few hours and put a new water fuel filter in (2nd this season). Fired right up and ran normal all the way home, 4000rpm no issue. I chalked it up to first time out for the season maybe little to much water in full from sitting all winter.
Taken it out several times since then, had the same issue. Always on the way out, about 45 mins into operating temperature. Will sit, run fine home. This weekend I pulled the distributor cap and rotor button off. All 8 of the terminals were corroded over. I couldn't even get the rotor button to slide off the shaft. Had to carefully cut the button off. The shaft was completely rusted over. Cleaned it, back to new with some sand paper and inspected it for anything significant....nothing found. I inspected the plug wires but the inside of the boots looked fine so I choose not to replace them YET.
Go out yesterday, boat starts up fine. Did feel like it was a little sluggish getting on plane, almost like we had 20 people sitting in the rear (we didnt). Eventually get on plane, ran fine at 4000rpm. Make it out to the same damn spot on the river (must be cursed) and it starts having issues. Not the same as before, started sporadically backfiring only between 2500-400rpm (first time for this). Lower rpm fine, but didnt like high rpm and would bog down again like normal. Turned it off, let it sit for 20 mins while the kids swam. Ran fine the last 10 mins of our ride. Sat another 5 hours then ran completely fine all the way home at 4000rpm.
By no means am I a mechanic but i have a decent understanding of how things work. I was initially leaning towards still something in the fuel, sloshing around and getting picked up which is why it works after boat sits for a bit. Tempted to drain my tank rather than keep going through water filters. Next step, rebuild the carb and put the new plug wires i have on. Im not the first owner, so no idea if its been done before. Then replacing all the fuel lines is also on table, boat is 18yrs old The back firing is interesting as it just started AFTER i put the new distributor cap on. But its sporadic so i go back to fuel or carb issue i guess.
Thoughts? thank you in advance for your time
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