Communication issues with 8.1’s

Okay......I'm missing something. You basically established the following:

The failure is like turning the key on-off really fast and because strb runs SmartCraft and gauges it make all helm readouts on-off crazy. The on-off also creates the RPM surge -/+400 RPM.

Why not run a fused 12 volt jumper and a ground wire directly to the SmartCraft display and take the engine harness out of the equation? It isn't a long term solution but if it really is power related...that should work and you can enjoy your boat.

The problem in tracing an engine harness is that it can be anything from a broken wire to a loose connector. The problem appears to be getting worse which means that it should stop working altogether at some point which in my opinion is easier to figure out. That said spiking power repeatedly to the SmartCraft display will cause it to fail.

I have chased this type of problem before.....and trying to find an intermittent power connection is a major time suck no one wants to pay for. The challenge with tracing is that the connections like this fail only when they have a load on them....so if your are just testing the wires with a DVM.....they look okay.....but they aren't.

The last one I worked on required hooking up a five amp light to the end of the circuit and then chasing it all the way back to the starter. In the end, it was a broken purple wire that had been improperly crimped but it took 3 days to find because the wires tested on a DVM fine.
 
What I would do is disconnect cannon plug, jumper #5 and #6 on engine side, briefly jumper 6 and 7 to start the engine. Unplug Smartcraft at the engine.
 
Again check the main positive battery connection AT the starter solenoid. You will need a zero degree ratchet and it is very hard to get to. MAKE sure you turn off your battery switch. All engine 12 volt power starts here I bet it is loose. Sometimes the engine might crank slower but not always.
 
Hello. Today we replaced the con cable from com bus to both engines. Boat ran great for 2 hours. Then at low speed in river alarmed twice. Went out to lake stopped boat turned everything offincluding keys and hadn't alarmed since. Was running about 4 hours today. Keeping my fingers crossed.
 
Hello. Today we replaced the con cable from com bus to both engines. Boat ran great for 2 hours. Then at low speed in river alarmed twice. Went out to lake stopped boat turned everything offincluding keys and hadn't alarmed since. Was running about 4 hours today. Keeping my fingers crossed.

Congratulations!!!
Thanks for the update and please let me know if you continue to be trouble free. I have had no time to work on the boat since my last post. We ordered a complete engine harness from Mercury, it should arrive this week. We have been using the boat at low speeds with the starboard motor pulsating (quick on/off) constantly - occasionally symptom free for 30 minutes then starts again. I cannot wait to find and fix this issue so we can enjoy our favorite boat!!

Have a great weekend
 
Thanks. I will keep you informed. I was so hopeful after running engine 2 hours and no alarms. But like I said, did it twice at low speed but after shutting everything down and running another 2 hours. No alarms. This is so weird. Please keep me updated on your progress also. How much did it cost for complete engine harness set? Com cable was reasonable. But of it starts up again I'm back to square one. Enjoy your weekend. Stay positive we will figure this out. Lori
 
With a small discount I believe the harness will be around $1100. I think I said earlier, we disconnected the data lines from the helm and it made no difference. I sincerely hope your problem is solved.

I will definitely keep this thread up to date.

Thank you
 
The update: We replaced the entire 8.1 wire harness with a new one from Merc Cruiser. The job took a few hours all the plugs fit and engine started right up with no beeps or RPM drops. Backed out slip and 20 feet away it all started again. Strb motor basically turning off & on quickly, but never quits running. Now thinking CFMonitors, we inspected and replaced both filters in CFM and the problem is still there.

We even power the ignition up with external power source. Next long shot tondisconnect smart craft data lines to see what happens - I know they are data only but it seemed to work for others here. I’m starting to hate our favorite boat ever! I’ve owned 10 Sea Rays and never had anything so frustrating. Check out page 4 for the list of everything we have done, Thx

Thank you in advance for your help
 
So last night out of pure frustration I disconnected both communication lines on top of each motor that feed info to the helm. I know everyone has said that cannot be the problem but it fixed something. Out of 1 hour of normal boating with one stop for an hour the starboard motor only faulted one time opposed to 40 times an hour. I may be on to something that was discovered by a few others on this thread. New wires or replace the smart craft system entirely??

More testing this weekend

Thank you….
 
I was having the same type of issue but for me it was a stall and instant restart that was happening about once every other trip out. We replaced the ECM before launch this year and it solved the issue after 3 years of chasing it down. Not a cheap fix but it took care of my issue.
 
Thank you, we actually swapped ECM from port to starboard and on/off issue stayed on the starboard side.

We are heading out again tonight to check it out.

Have a great weekend
 
Thank you, we actually swapped ECM from port to starboard and on/off issue stayed on the starboard side.

We are heading out again tonight to check it out.

Have a great weekend
So I did the same thing and thought the same but was told that the ECM is programmed Stbd or Port so the instruments will still show on Stbd. If you are experiencing this idling in the slip I would just start the Stbd motor and see if you see the issue to truly rule it out.
 
Day 3 of running with both communication lines disconnected and the starboard engine on/off has stopped completely. Yesterday was the first time this year we could get the boat on plane running about 3800RPM. So now what?? I’m thinking about replacing communication lines, upgrading to NMEA2000 and replacing Smart Craft. I’m sure there’s a thread out there but any tips would be appreciated
 
So ran the boat today about 5 hours, alarmed about 15 times. So frustrating. When I lost the digital display on smartcraft and all port side gauges went out boat ran fine. Then boat alarmed gauges came back on and it would bog. Don't buy Com cables. That's not what is wrong. It helped some but not the core of the problem.
 
So sorry to hear!! We have been running perfectly with the comm lines disconnected at each engine. So I’m running no gauges or VV mobile at helm. Today we have reconnected comm wires at engine and disconnected Smart Craft plugs at helm to see what happens. Must have gauges at helm so I’m looking forward to finding the solution but I feel we are getting very close. I will likely upgrade to NMEA2000 and vessel view 502. Everyone (including Merc Tech) has said comm lines provide info only but our boat runs perfectly with lines disconnected??
 
So sorry to hear!! We have been running perfectly with the comm lines disconnected at each engine. So I’m running no gauges or VV mobile at helm. Today we have reconnected comm wires at engine and disconnected Smart Craft plugs at helm to see what happens. Must have gauges at helm so I’m looking forward to finding the solution but I feel we are getting very close. I will likely upgrade to NMEA2000 and vessel view 502. Everyone (including Merc Tech) has said comm lines provide info only but our boat runs perfectly with lines disconnected??
That harness is more than just Smartcraft. The keyswitch and other things are a part of it. I would take a look to see if you are getting a voltage dropout on the Red wire in this diagram. The keyswitch may just be the culprit. Also the purple wire comes from the lanyard safety switch which supplies the power to the keyswitch. If any of that power gets interrupted both the Smartcraft instruments as well as the engine will react.
upload_2023-6-25_10-25-7.png
 
Did mercury tech hook the computer to your engine. The smart craft never shows any faults or alarms.
 
Did mercury tech hook the computer to your engine. The smart craft never shows any faults or alarms.

Yes, the lap top recorded multiple faults like cam sensors, fuel psi, throttle position ETC. We sent recording to Mercury for detailed analysis and found nothing. Noting most of the faults were do to the starboard motor turning off/on quickly
 
Yes, the lap top recorded multiple faults like cam sensors, fuel psi, throttle position ETC. We sent recording to Mercury for detailed analysis and found nothing. Noting most of the faults were do to the starboard motor turning off/on quickly
 
So frustrating. Why they ever put a computer on a boat engine. If they can't find the problem, Sounds like we are on our own.
 

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