I have a 99 SeaRay with twin 7.4MPI inboards. The port engine just developed a strange problem that I need some help with.
At all RPMs below 4,000, it occasionally starts running VERY rich and power and rpm drops way off. It will do this sometime for just a few seconds and other times for minutes. I have a Floscan and when the problem occurs, the fuel flow will jump way up. For example, at idle it will jump from about 1.2 gph to 5 gph or more. At 2,200 rpm (about the fastest it will run when the problem occurs), it jumps to something like 19gph or more. When the problem occurs, you can smell the strong odor of the unburned fuel. It does this both when the engine is basically cold and when it is fully warmed up.
If above about 4,000 rpm it runs just fine and the problem does not reoccur until I slow back down and the rpm drops.
This weekend, the problem took on a different nature. Now, the opposite is happening. The fuel flow is very low (lean) for the engine speed and load, and the engine is running VERY rough. For example, it is only showing about 5.5gph at 2,500 rpm, about the fastest it will now run under any circumstances. The problem is now also no longer intermittent and is occurring constantly.
Water temp is normal, oil pressure is normal and battery voltage is about 13.8. It did this once before about two years ago and the Mercruiser tech put a scan tool on it and saw no codes. At that time my alternator on that engine was a little weak (about 12.5 volts) and the feeling was that it may be a voltage problem. I replaced the alternator and the problem did in fact go away. However, I am now thinking that it simply cured the symptom not the cause as the current 13.8 volts should be fine I think.
Any idea on what could cause this and what I might look for?
Thanks!
Tom
At all RPMs below 4,000, it occasionally starts running VERY rich and power and rpm drops way off. It will do this sometime for just a few seconds and other times for minutes. I have a Floscan and when the problem occurs, the fuel flow will jump way up. For example, at idle it will jump from about 1.2 gph to 5 gph or more. At 2,200 rpm (about the fastest it will run when the problem occurs), it jumps to something like 19gph or more. When the problem occurs, you can smell the strong odor of the unburned fuel. It does this both when the engine is basically cold and when it is fully warmed up.
If above about 4,000 rpm it runs just fine and the problem does not reoccur until I slow back down and the rpm drops.
This weekend, the problem took on a different nature. Now, the opposite is happening. The fuel flow is very low (lean) for the engine speed and load, and the engine is running VERY rough. For example, it is only showing about 5.5gph at 2,500 rpm, about the fastest it will now run under any circumstances. The problem is now also no longer intermittent and is occurring constantly.
Water temp is normal, oil pressure is normal and battery voltage is about 13.8. It did this once before about two years ago and the Mercruiser tech put a scan tool on it and saw no codes. At that time my alternator on that engine was a little weak (about 12.5 volts) and the feeling was that it may be a voltage problem. I replaced the alternator and the problem did in fact go away. However, I am now thinking that it simply cured the symptom not the cause as the current 13.8 volts should be fine I think.
Any idea on what could cause this and what I might look for?
Thanks!
Tom
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