Motor's internal hour meter

[Stripehunter]

Another stupid question--I'm assuming the hour meter in the motor's computer ticks on run time and not ignition time. I just installed installed a panel mount hourmeter (ticks on ignition on; not a problem since I never leave the ignition on without the motor running). Now the issue is I've been running the boat for a couple of months before installing the hourmeter. When the boat next goes in for service, I will have them tell me the hours on the cpu so I can run the panel meter to get them close. Is there any harm (aside from battery drain) in leaving the ignition on for long periods of time without running, or would it just be best to pull the meter back out, disconnect it, and put a battery to it?

[Floatingduck]

If you leave the ignition on the only thing that you will do will drain the battery, you will not hurt anything else. If you do run the hour meter straight into the battery use a fuse just incase you have a short in your hour meter and you don't want to burn the place down.

[angler53]

When I took my boat in for the 20 hour motor check they told me the ECM said 24 hours. I had one of those inductive type hour meters and it read low by 4 hours. I purchased a Hobbs meter and hooked to the battery and ran it up to 24.0 hours then installed it in the panel. Last week it was in for service and the Hobbs said 104.8 the ECM said 100 hours. I don't recall the accuracy of the Hobbs but 4.8 hours in ten months is an awful lot. I know it takes a few seconds from switch on to start up and I do turn the ignition on to check fuel quantity from time to time, But still, 4.8 hour is a big difference. One of the two devices don't keep good time. I guess its a good thing the motor says I have less time on it.

[yarcraft91]

If you assume the Hobbs is wrong and the ECM is right, the Hobbs is running 6.3% fast- I expect that would not meet their specs. It's entirely possible neither device keeps good time. I expect you noticed that your ECM and hour-meter times differ now by 4.8 hours, which is within 1 hour of the the adjustment you made to that Hobbs meter. Have you seen running-time printouts from the ECM or are the shop people giving you that number verbally?

[angler53]

If you assume the Hobbs is wrong and the ECM is right, the Hobbs is running 6.3% fast- I expect that would not meet their specs. It's entirely possible neither device keeps good time. I expect you noticed that your ECM and hour-meter times differ now by 4.8 hours, which is within 1 hour of the the adjustment you made to that Hobbs meter. Have you seen running-time printouts from the ECM or are the shop people giving you that number verbally?
The tech told me that there was a difference between the ECM and the panel meter. I didn't see for myself. I use to rent airplanes by hobbs meter time so maybe they are designed to run fast.

[Jimmy Jig]

What possible difference would it make if there is 4.8 hrs. more or less on the motor? I change oil every year or 100 hrs. It is ran 4.8 hrs more I wouldn't worry too much that it would harm the motor.

[angler53]

What possible difference would it make if there is 4.8 hrs. more or less on the motor? I change oil every year or 100 hrs. It is ran 4.8 hrs more I wouldn't worry too much that it would harm the motor.
Yesir, you're right and who sives a ghit anyway, its just information. I just thought it was a little strange and worth mentioning. Hobbs meters are known and trusted for being highly accurate instruments used in any environment.
If I remember correctly, I was told that when the clock starts slowing down in an ECM, death of that module is pending. Who knows, time will tell...lol

[dbowhntr]

The ECM tracks time from run time and not crank time. There is a transitiion phase internally to the module thats goes from crank to run. There is some delay in this transition.