7.4 merecruiser bogging down

[lparkinson]

I have a 2001 7.4l MPI Mercruiser IO in a 23’ Sea Ray with 800 hours of service. It has recently had a complete tune up and the water separating fuel filter replaced. The engine starts good and runs fine at idle. The engine powers up to cruising speed (3500 rpm’s) and runs fine for 2 – 3 hours then it will suddenly drop back to 2600 rpm’s. It will remain at 2600 rpm’s no matter how much the throttle is increased. When the throttle is returned to idle, it again runs fine and will then power back up to cruising speed but only for 15 – 30 minutes before dropping back to 2600 rpm’s. When the engine is turned off for several minutes, it will start fine and power up to cruising for about an hour before dropping back to 2600rpm’s. Besides the tune up and fuel filter change I have ran 3 cans of Sea Foam through the engine with fresh gas with no improvement. I am reluctant to take it back to my mechanic and randomly start replacing parts without identifying a potential cause. Can you help??

 

[sprink56]

This is probably a long shot but it can happen. Look for any leak in a coolant line even as small as a pin hole that might be spraying on some electronic part. This might be causing an electronic shut down untill it drys enough to work properly. As the RPM increases and the leak increases you get enough moisture to cause a repeat.

I know this is a reach but it is worth a look.:thumbsup:

 

[tdappleman]

What was done as part of the tuneup? If the coil wasn't replaced - I'd check that to see how hot it gets when the failure occurs. A coil on it's way out can cause this level of intermittent power loss.

 

[4 Lollipops]

I had similar problems with same engine and similar hours. Replaced plugs, wires, distributer cap & rotor. Works fine with new parts. Good Luck.