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Old 10-13-2021, 04:13 PM   #21
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Originally Posted by gsholz View Post
Data on these serial buses comes in packets of zeros and ones with voltages ranging from 1.5 to 3.5V. You do not need to decode the packets to diagnose failures. Anything that disturbs the signals significantly would lead to no communication. Then it is just a matter of disconnecting modules on the bus until the data signals are restored as long as you have at least one good talker on the bus.

To identify the differential data wires (CAN bus high and low) look for wires that are twisted together to eliminate common mode interference.

Any good tech should be familiar with the above. Any car after 1995 is CAN bus based.
In this particular case, that approach would not identify the problem. When I reveal the exact cause of the problem, which is what makes it so hard to diagnose, you will see why.
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Old 10-13-2021, 08:34 PM   #22
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If all else seems to be ok look for an external factor. It’s something external to the network that is corrupting the data. It is probably close to the wiring harness and could be an unshielded data cable from another network, a power supply of some kind, or some other active electrical component.
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Old 10-15-2021, 05:24 PM   #23
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I'm getting bored - give us the answer!!!
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Old 10-15-2021, 05:56 PM   #24
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The short answer is that the flybridge starboard side stop button failed. That button is a normally CLOSED (backwards from most, in my experience) momentary switch. Pushing it is supposed to open a circuit thereby shutting down the ECM. This button was always OPEN, as if the stop button were continuously pressed.

Especially difficult to diagnose because, even if I had disconnected everything (ie, all of the start and stop buttons, both sets of displays and all 6 throttle controls), the symptoms (no data from ECM) would have been the same. In retrospect, knowing the pinout (which I couldn't get) would have allowed me to confirm continuity between those pins, and the lack of continuity would have pointed me straight to the stop buttons. Anyway, I disconnected the starboard side switch and wired its leads together. Engine starts right up with full data. New switches on order.

Ironically, the stop button on the port side (of fly bride) also failed, but it failed to always OPEN, even when pressed. As a result, it didn't stop the engine from starting, but it would not have shut down the engine. I never noticed because I always start and stop from the PH. For both of those buttons to fail is surprising to me. They are both original equipment Cole Hersee, well protected from the elements on the back side, and fitted with rubber covers on the front side. There is no visible damage, water intrusion, etc., on the rear (or front).

Thanks for playing, and good guesses all around.
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Old 10-15-2021, 06:12 PM   #25
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Well, I never would have guessed that one.
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Old 10-15-2021, 06:15 PM   #26
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Well, I never would have guessed that one.
Thank you, that is reassuring, especially coming from you. And I figured it is useful information in case anyone else gets stuck with something even similar. What I really needed was a pinout.
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Old 10-15-2021, 07:27 PM   #27
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May I ask what type and year your boat is sir?
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Old 10-15-2021, 07:52 PM   #28
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Thank you, that is reassuring, especially coming from you. And I figured it is useful information in case anyone else gets stuck with something even similar. What I really needed was a pinout.
Definitely a weird one. And it supports my idea that the most important thing about any electronic system is having access to the tools and information needed to diagnose it.
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Old 10-15-2021, 08:02 PM   #29
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Did you mean to say the port side failed always closed instead of open? Failure open would be like the starboard motor. Or am I confused?
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Old 10-15-2021, 10:20 PM   #30
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Did you mean to say the port side failed always closed instead of open? Failure open would be like the starboard motor. Or am I confused?
Exactly. Both switches bad. Starboard stop switch was always open (as if pressed to stop the engine) and port was always closed' even when button was pressed, so it could not be used to stop the port engine. Note that the bad port side switch had nothing to do with my problem on the starboard side.
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Old 10-15-2021, 10:22 PM   #31
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May I ask what type and year your boat is sir?
Mikelson Nomad' commissioned in 2009. Problem is not with original construction as much as Cummings design of QSM 11' and Cole Hersee switch.
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Old 10-15-2021, 11:58 PM   #32
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Mikelson Nomad' commissioned in 2009. Problem is not with original construction as much as Cummings design of QSM 11' and Cole Hersee switch.
Thanks. I have QSCs of the same year with the same stop buttons so thanks for sharing your experience with us.

I may get the switches replaced as a precaution.

Magnificent boat btw.
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Old 10-16-2021, 05:26 AM   #33
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Thank you, that is reassuring, especially coming from you. And I figured it is useful information in case anyone else gets stuck with something even similar. What I really needed was a pinout.

I had a pair of Cummins QSC 8.3 in a former boat, and I was able to find a long and dense wiring manual. As I recall it showed all the harnesses, where all the options connect, different configurations, etc. And I think it was down to the pin numbers. I might still have it and can send to you. I don't know if it's applicable to the QSM, but at least it might show you want to look for in terms of documentation.
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Old 10-17-2021, 09:46 AM   #34
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I had a pair of Cummins QSC 8.3 in a former boat, and I was able to find a long and dense wiring manual. As I recall it showed all the harnesses, where all the options connect, different configurations, etc. And I think it was down to the pin numbers. I might still have it and can send to you. I don't know if it's applicable to the QSM, but at least it might show you want to look for in terms of documentation.
That would be great. PM sent. Thank you! -Rick
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Old 10-17-2021, 11:51 AM   #35
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Does the stop button shut power to the ECM, or just provide a signal telling the ECM to shut down?

If there are multiple stations, then the normally closed, momentary open is the easy way to produce the logic (wired AND function). Similar to the way machine tool E-Stop chains are wired.

With a wiring diagram, it would have been easy to notice and check. If this is the way QSMs are commonly set up, I'd be a little disappointed in the expertise of the Cummins technician that looked at it.
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Old 10-17-2021, 01:41 PM   #36
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Does the stop button shut power to the ECM, or just provide a signal telling the ECM to shut down?

If there are multiple stations, then the normally closed, momentary open is the easy way to produce the logic (wired AND function). Similar to the way machine tool E-Stop chains are wired.

With a wiring diagram, it would have been easy to notice and check. If this is the way QSMs are commonly set up, I'd be a little disappointed in the expertise of the Cummins technician that looked at it.
I would think that normally open could be just as easy with multiple stations -- perhaps easier -- just power a pin monitored by the ECM. The normally open approach requires the use of two pins and prevents the diagnostic approach (suggested above) of disconnecting everything any adding stuff back until the offending item is found.

I did ask for wiring diagrams and was told every boat is different. Even so, a generic diagram should still be easy to provide. A pinout would have been sufficient, but I couldn't get my hands on that either. Pretty frustrating.
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