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1997 7.4 mercruiser mpi surge

C

c5homer

New member
hey guys maybe you could help working on my cousins searay with twin 7.4 mpi's. when trying to run above 3000rpm starboard engine starts surging. going to take a fuel pressure test tonight. anything else come to mind. he just bought the boat and i found upper plenum gaskets on floor of boat. looks like someone has been trying to fix this concern.
 
filters clogged. both motors run off the same tank maybe water in one tank that feeds that motor.

Also air getting into the system check every hose.

Yep check fuel pressure pumps giving.

In the end you could always change the pumps see if the problem follows the pump to the other motor.
 
check the hose running to the MAP sensor. if possible, TEE a vacuum gauge into that hose and see what the vacuum is, especially when the surge starts.
 
I have the same or similar problem on my friends 1998 454 merc bravo 3 thunderbolt V ignition. the engine runs normal until it gets up to temp and them starts bogging down and surging. You have to throttle back to stop the surge and eventually can't even get 2500 rpm. Plugs, wires, cap, rotor, fuel filter, all new. cleaned flame arrester, treated fuel for water. Replaced carb and coil with known good units for troubleshooting, No help. Suspect ignition module or pick-up sensor breaking down as they heat up???
 
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