A few weeks ago I tried to start my 2005 Mercruiser 5L MPI engine after three days docked, and it turned over but stalled. I tried 3 more times, and finally had to run up the throttle to get it to keep running. Once it warmed up, I could bring the throttle back down and it would not stall. I'd been noticing a fluctuation in RPM when first starting up, but this is the first time it stalled. Since then I've been able to start it (in my driveway) and I still hear the up and down RPMs, but it doesn't stall.
I recently bought an engine scanner, and recorded some data while starting the engine. I'm not a mechanic so I don't know what "normal" should look like, but the things I'm seeing don't seem right.
I've attached two plots of the data here. The first plot shows battery voltage, engine rpm and oil pressure. You can see some fluctuation of the engine RPM, but it's not huge. It goes from the high 400's to mid 600's. There is also a huge voltage drop during startup. Of course that's when the current demand is the highest, so I would expect some voltage drop, but here are my questions:
1. Is the rpm oscillation normal, or should it be flatter around 600 rpm?
2. Is the voltage drop to around 8 volts normal, or is that maybe an indication of a weak battery?
I attached the second plot where I replaced oil pressure with spark advance. The spark advance moves around quite a bit during idle - from about 2 degrees to 15 degrees. So I'm wondering if this is normal?
Thanks in advance for any help,
Tom
I recently bought an engine scanner, and recorded some data while starting the engine. I'm not a mechanic so I don't know what "normal" should look like, but the things I'm seeing don't seem right.
I've attached two plots of the data here. The first plot shows battery voltage, engine rpm and oil pressure. You can see some fluctuation of the engine RPM, but it's not huge. It goes from the high 400's to mid 600's. There is also a huge voltage drop during startup. Of course that's when the current demand is the highest, so I would expect some voltage drop, but here are my questions:
1. Is the rpm oscillation normal, or should it be flatter around 600 rpm?
2. Is the voltage drop to around 8 volts normal, or is that maybe an indication of a weak battery?
I attached the second plot where I replaced oil pressure with spark advance. The spark advance moves around quite a bit during idle - from about 2 degrees to 15 degrees. So I'm wondering if this is normal?
Thanks in advance for any help,
Tom