Merc 5.0l. EFI. S/N 0M0 69661
680 hrs on engines
Twins in Chap 280ssi
This spring, port engine ran really rough on 2nd or 3rd outing. It started running rough pretty suddenly, I did not notice a sudden change at a single point in time. It was more like after an acceleration to plane, " that didn't feel or sound right". At that point it was idling pretty rough.
Tuned up both engines, spark plugs (with proper gap), spark plug wires, rotor, cap and fuel filter. The components coming out showed some wear, but not that bad and parts from both engines appeared the same.
This improved the situation, but did not cure it. The engine starts fine, but at idle, it will randomly appear to loose everything for a fraction of a second (like you turned it off for a millisecond) and then comes back to life. The idle increases momentarily as it recovers and then returns to "normal". This is truly random, sometimes a minute between stumbles sometimes linger or shorter.
Under load the engine is running rough and appears to lack power. This engine lags RPM over the other engine (based on tach on the dash). At roughly 3000 RPM, if I firewall the starboard engine it springs to life and approaches 4500 rpm pretty quickly and sounds great. If I do this with the port engine, it slowly gets to about 4000 Rpm (slow being a few seconds vs almost instantly with the other engine).
Being a holiday weekend and easy to do, I went ahead and changed the ignition sensor in the distributor. No change. This morning I swapped fuel lines from the tank, no change.
The only other symptom is there is a light "tap" from the engine, the out drive is a little noisy (as opposed to the starboard engine) and there is a random chirp sound (really random) from some where else on the engine.
I assumed since the tune up almost fixed, it was ignition related. Now I'm guessing fuel? Any other sensors or electricl components that could cause this? I don't have any instruments to check the fuel pump. Would like to avoid hauling the boat mid season. Any help appreciated.
Thanks in advance.
Any help
680 hrs on engines
Twins in Chap 280ssi
This spring, port engine ran really rough on 2nd or 3rd outing. It started running rough pretty suddenly, I did not notice a sudden change at a single point in time. It was more like after an acceleration to plane, " that didn't feel or sound right". At that point it was idling pretty rough.
Tuned up both engines, spark plugs (with proper gap), spark plug wires, rotor, cap and fuel filter. The components coming out showed some wear, but not that bad and parts from both engines appeared the same.
This improved the situation, but did not cure it. The engine starts fine, but at idle, it will randomly appear to loose everything for a fraction of a second (like you turned it off for a millisecond) and then comes back to life. The idle increases momentarily as it recovers and then returns to "normal". This is truly random, sometimes a minute between stumbles sometimes linger or shorter.
Under load the engine is running rough and appears to lack power. This engine lags RPM over the other engine (based on tach on the dash). At roughly 3000 RPM, if I firewall the starboard engine it springs to life and approaches 4500 rpm pretty quickly and sounds great. If I do this with the port engine, it slowly gets to about 4000 Rpm (slow being a few seconds vs almost instantly with the other engine).
Being a holiday weekend and easy to do, I went ahead and changed the ignition sensor in the distributor. No change. This morning I swapped fuel lines from the tank, no change.
The only other symptom is there is a light "tap" from the engine, the out drive is a little noisy (as opposed to the starboard engine) and there is a random chirp sound (really random) from some where else on the engine.
I assumed since the tune up almost fixed, it was ignition related. Now I'm guessing fuel? Any other sensors or electricl components that could cause this? I don't have any instruments to check the fuel pump. Would like to avoid hauling the boat mid season. Any help appreciated.
Thanks in advance.
Any help
