Communication issues with 8.1’s

Three Seasons

Long time member
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Jun 10, 2009
254
Minnetonka
Boat Info
380 Sundancer 2006
Engines
Twin 8.1 V-Drives
Where to start looking? Last night both tach lights & gauges would turn off for a few seconds then hear one Beep and a quick RPM drop on both motors simultaneously then go back to normal. All this was happening numerous times with no consistency for 30 minutes until i got back to dock.

I had reported this issue last April thinking it could be a NMEA issue and at that time would only happen to one motor S or Port and not very often. Since that time I have replaced all 4 batteries and checked all grounds. Even took your recommendations of a slow power up and starting starboard motor first.

http://www.clubsearay.com/index.php?threads/nmea-network-issue.108810/

Thank you in advance for any recommendations.
 
What's the output on your alternators? Possibly one was going bad in April and now they are both going bad? Just a thought because I know they can be finnicky with low voltage
 
I had a Merc Tech out today to read codes. Everything was normal except for 16+ code faults for the starboard TPS (Throttle Position Sensor). I will replace the TPS and hope the issue stops.

Thank you
 
Had same issue with our 496mags. (8.1s) Chased it around for 3 seasons. Scanned the motors, notta. Checked the fuel pressure, notta. Checked the eectrical system, notta. Removed and cleaned ALL the electrical connection POS and NEG on the motors, notta. Replaced the helm ignition switched, notta. Then decided to upgrade from the SC5000 to VV703, also adding NMEA2000 network, SeaStar Steering, MFD display, AP and a bunch of other stuff. Found a spliced camm bus data cable running to the Port motor from the SC5000. It was apparently cut by the PO or a tech and rather than replace it, ($89.00) they repaired it. Ended up replacing both of these cables. After the cable replacement and VV upgrade, it stopped. Also, my Merc guy asked me did I always power the engines down all the way at the end f the day. I told him I left the breakers and keys on often. Just used the dash switches routinely. He advised to shut everything down in this order: helm toggles, key switches and then breakers. Power back up in opposite order. The SmartCraft and VV systems are computers and just like your laptop and phone, need to be restarted regularly. Not sure what fixed it, my theory is the spliced cable (it is a camm bus cable like an ethernet cable). Anyways, just never know what you will find from PO or even service techs past goof ups. It is definitely a connection or computer issue, as when it happens it is like a quick reboot. I feel your frustration, as it was certainly frustrating for me.
 
Replaced two TPS and the problem is still there (no surprise to Korkie, thx for the great info). Agreed, its very likely a connection or computer issue. Beeped with RPM drops 20 times last night for the first 30 minutes we parked for dinner and powered down. On the way home didn’t do it at all. Driving me CRAZY!
Looks like its cable inspection time…Fun.

Thank you
 
Try these first. Make sure batteries are off. Best to disconnect grounds so absolutely sure no power. Unplug and spray with electronics spray cleaner and replug everything to do with smartcraft. Especialky the junctions behind the gauges. Also, always turn your key switches off when powering down for longer than an hour or so. I do mine all the time. Check your connections on back of alternator and grounds on back off motors. Make sure clean and tight. Power to computers comes off the solenoids at the starter. Need to check those, mine were a $#@&+ to get to. My thought is with this occurring so often one outing and not at all the next, something is either dirty or loose. Good luck.
 
Hey. I have a 2006 38 Sundancer that is doing the exact same thing. 3 years ago I replaced the ECM on starboard engine. Problem gone now this year the exact same thing is happening on port engine and starboard started to act up to. I've had multi mechanics look at it. Merc scan done and nothing. I'm at my wits end. Frustrating
 
Did your engines bogg down for a second when this happened. Mine bogg then go right back to normal
Sometimes, there is is quick loss of power, the gauges all shut off and then power back on. I can't duplicate it and there are no codes showing on the SC5000. It typically happens right at start-up. There is one beep and sometimes the engine stalls if cold.
I have had it happen when up on plane. Sometimes the starboard gauges all shut off until I restart the engine.
I have heard its a problem with the CPU and that Whipple can repair them. For now, mine only do it at start up.
 
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Sometimes, there is is quick loss of power, the gauges all shut off and then power back on. I can't duplicate it and there are no codes showing on the SC5000. It typically happens right at start-up. There is one beep and sometimes the engine stalls if cold.
I have had it happen when up on plane. Sometimes the starboard gauges all shut off until I restart the engine.
I have heard its a problem with the CPU and that Whipple can repair them. For now, mine only do it at start up.

Yes, Exactly the way my issues started last year, once at start up (4 to 6 minutes). Now does it constantly. Finally have time this weekend to follow Korkie’s recommendations to power down and clean and inspect connections and connectors. I hope to follow-up with the fix, this is driving me crazy!

Thanks
 
Hi. Just wondering if you had any success diagnosing the communication fault. Had another mechanic look at it unsuccessful. Suggested what Sam said to try but he didn't do it. Plan on calling Port Clinton marine max again. Thanks for any info you can share.
 
Last Saturday I spent about 4 hours at the helm and engine compartment unplugging and cleaning connections with marine grade electrical connection cleaner (that just means i paid more for “marine grade”). I focused more on the blue CAN network plugs and all 3 large plugs on the ECM’s. I am amazed at how many connections there are and I probably only cleaned 30% of what’s there.

Happy to say the engines did NOT fault one time on my 30 minute ride home. That said, I am cautiously optimistic the problem is solved or at least isolated to the CAN network. I’m looking forward to more boat time this weekend and HOPE I can continue to report a positive result.

Stay tuned…
 
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2nd day of running after cleaning. Ran about 35 min and starboard motor beep & RPM serge one time at about 6 minutes. Thats so much better that 20 times in 30 minutes. So still scratching my head but feel I’m heading in the right direction that the issue is cable or connection related.
 
Interesting. I did mine. Haven't taken it out yet but was thinking same thing, may have to replace cable. Thanks again for sharing info.
 
I’ve been battling this issue with my starboard motor intermittently for e past 3 season I’ve had this boat. Will usually only happen once per trip but every trip and about half the time at idle and half the time while running at speed. It has stalled on rare occasions and mostly just beeps, hesitates and goes back to normal in a split second. My mechanics checked all the grounds and wires, changed the relays and changed the crank position sensor but none of this helped.

I only shut down the motors with the switches on the dash but will try @Korkie ’s suggested shut down procedure (helm toggles, key switches and then breakers). Hoping this helps!
 
Day 3 after cleaning. Continues to be an issue but only a few times, so frustrating. Sorry to hear of others with the same issue but believe this information will lead us to the fix. I will reach out to Mercury Marine support to ask if they have any ideas, this is obviously happening to many boats with 8.1’s.
 
There are a few boats in my marina with the same issue and my mechanic says he’s had multiple reports from other marine service companies in the area.

I tried the shut down procedure above last night and then again after anchoring out today from 4 hours. Both trips shutting down the right way exhibited the same issue. It was worth a try. Thanks @Korkie
 
I am convinced it is a communication issue as mine was finally addressed after the upgrade to VV. The momentary shutdown and gauge fluctuation took 4 seasons to finally find. With the spliced comm cable we found and reconfiguring and changing some of the junction connections behind the gauges, one of those items was causing the issue. You would think SR would have a service bulletin on this, but i don't think they have a clue either. The issue I have with my RPMs varying up and down was certainly my fuel system. Once that was replaced, that issue went away.
The comm cables are only $120.00. May be worth a try to purchase one or two, I say 2 because it could be either one, and just run them directly from the dash to the motors and see if that resolves anything. I am not one for just throwing $$$ at a problem w/o justification, but it was a pertinent part of what resolved mine. After all, they are only ethernet cables and they can go bad. Especially after 15-16 years.
 

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