8.1 Mercruiser Problems

... Long story short, there were 5 dead spark plugs. How that is even remotely possible , I do not know...

Do you know if when the engine was winterized they "fogged" it. That is known to foul these plugs and that the the recommended method is to feed from a premix tank with a blend of gas, 2-stroke oil and stabilizer.

-Kevin
 
One more thing to think about, there's alot of engine guys that feel that .060 is just too much gap for that 8.1 and putting a strain on the ignition and have had good results dropping down to .045. I would be leaning in that direction.
 
I've got 2 sets of plugs, "million $" plug wires and fuel filters being installed later this week.....hopefully, anyway. I developed a significant miss last week and could smell unburned gas in the exhaust. Also hoping that's all that's needed.
 
KevinC...I winterize it myself and never fog

scoflaw...I've always thought .60 was a bit much. I have never seen another plug gap on all the machines I've owned that was that wide.
 
“timeflys...I used to fly an ST-27 in the 80's. The good old Saunders , now residing in museums...”

Small world …. So did I..I used to work for Atonabee…
Hope your mtc issues are behind you for the summer.
Peter Glazier
 
I remember you Peter. You guys flying into Toronto Island as well as us at Voyageur.
I worked at Air Atlantic after Voyageur flying Dash 7's and 8's under one of your Atonabee comrades , Peter Bing.
Steen Jensen
 
Sejensen737 - I’m glad to hear you located your 8.1 problems and I currently share your frustrations with our 2006 8.1’s. I’m about ready to send my PCM’s to Boats Unlimited and then I stumbled on this well written thread with great information. I started the attached thread a would really appreciate your opinion as well as anyone else’s thoughts. In summary my engines start and run great but have this strange electrical fault. I attached you tube video on the final page. Boat is in storage until April.

http://www.clubsearay.com/index.php?threads/communication-issues-with-8-1’s.110654/

Thank you in advance for reviewing - Help!!!
 
Hi Three Seasons
I just read through your thread and watched the YouTube video
The thing that strikes me is how BOTH sides go dead at the same time while the engines continue to run fine
My first thought is a problem ground or power input to the gauge clusters if there is such a thing.
Usually machines with two engines (airplanes,boats)have totally separate systems to allow you to get home on one
It appears that the gauges have a common power source and or ground
I would start looking under the helm for just that and better yet get a hold of a schematic that might reveal such
Good luck
 
Hi Three Seasons
I just read through your thread and watched the YouTube video
The thing that strikes me is how BOTH sides go dead at the same time while the engines continue to run fine
My first thought is a problem ground or power input to the gauge clusters if there is such a thing.
Usually machines with two engines (airplanes,boats)have totally separate systems to allow you to get home on one
It appears that the gauges have a common power source and or ground
I would start looking under the helm for just that and better yet get a hold of a schematic that might reveal such
Good luck
Have you guys verified both the 12V Pos and Neg are stable at the Smartcraft J-boxes? When the keyswitch are turned on there should be constant power up through the entire Smartcraft network. It looks to me like it is a power issue rather than loss of ECM comm. If for example the power dips when there is a load on the network it will reboot - power that dips is a sign of a bad electrical connection. Pin A is +Bat and Pin B is -Bat on the 10 pin connectors. Get a good DVM connected and watch that as the problem occurs. Lastly, If there is a major comm issue then the system may also reboot - this issue may be due to the lack of terminating resistors on either end of the network.
 
I was working the other day and thinking of your problem. A 737 has all essential electrical equipment on a hot battery bus. Designed that way so the engines keep running if you have massive electrical problems. The left and right set of flight instruments operate independently so that if one side fails you can rely on the other side. There have been instances when both sides failed due to a short on the buses and a failure of the transfer relay. Thankfully there is a third standby set of instruments (that are on the hot bus because when you need them you need them real bad) to get you home in this unlikely event.
So...I'm wondering if you have an intermittent short on the buss that supplies power to the instruments. It makes sense that a loose/shorting connection would cause your fault multiple times on a trip due to vibration/rough water. That both sides are failing at the same time is an important clue. I tried to find a schematic on line to check this out but was unsuccessful and my schematics are on the boat a 1000 miles away. I know I'm comparing boats vs airplanes but I think engineering design principles may be similar. Anyway , I think this might be worth exploring.
 
ok, the boat after injectors were cleaned today ran Amazing.
2500 RPM to over 4500 and humming like a bird.
So, I am learning so much about these 8.1 HO motors.

The injectors were so badly clogged they were causing much more noise and vibration. Also noise from the V drives it sounded like.

Boat ran like new after I installed clean injectors. 4 out or the 8 were clogged.

Now onto impellers

cheers
How did you determine your injectors were clogged? I have 2006 twin Mercruiser 8.1 Horizon 496. Ran fine last fall. Started right off the dock this spring in guardian mode. I had shift gear alarms on both engines. Replaced shift switches. Alarm stopped but it is still in guardian mode. I bought the Diacom test program and found no issues on port engine except I did not test any of the engine items such as spark etc. Motors run fine in neutral. But starboard side would not even connect to Diacom program as there was only 5 volts at the test plug. Diacom/Rinda said that there has to be at least 12 volts at the test plug. Anyone have any ideas why the voltage is low? Batteries are brand new and fine. Does the test plug come directly from Module?
 
2006 340 8.1 Horizon 300hrs port engine

Last year it became hard to start. It would idle rough and stop. Required restart 3 or 4 times until it would continue to idle. Any application of throttle would cause it to stop running. If it would continue to idle rough and warm up it would accept throttle inputs and accelerate and run fine. Once at this point leaving the dock and going out in the lake resulted in flawless performance. Shutting down at anchor in the lake with a restart a few hours later the engine starts and idles normally.
Checked IAC filter. Tested IAC valve. Filter a little dirty and IAC valve checked OK. Replaced filter and IAC valve anyway. No improvement.
Launched boat a few weeks ago. Replaced fuel filters in Cool fuel Module before launch. Both were a little dirty but not excessivley so. None of the "loose paint" problem evident. Same symptoms on first start up of the year. Took it for a run and it ran well. Back to dock and tried to start a few days later. Ran for 10 seconds first attempt. Ran for 5 seconds second attempt. Would not start after that and exhibited what I can only describe as "starter kickback" on next attempt. Decided not to push further until examination. Was afraid of possible hydrolock. Pulled all plugs , which by the way only have about 30 hours on them. None were wet with water. No water in oil. Removed left exhaust manifold to inspect. Gasket was not compromised. No sign of internal water damage but the outer manifold was quite rusty , which is why I removed that one rather than the easier right side. Pressure tested it and it appeared not to leak. Borescoped exhaust ports and all 8 cylinders and no abnormalities noted. Turned engine over with plugs out and manifold off and no abnormalities noted.
So ...a ton of work and still no obvious faults. I'm thinking now , possibly bad injectors?
Any ideas?


Alright, so you've done some solid detective work on your boat engine, but the issue is still giving you a headache. Here are a few more things you can check out:

  1. Fuel Quality: Make sure the fuel you used is fresh and clean. Old or bad fuel can really mess things up.

  2. Fuel Pump: Check if the fuel pump is doing its job properly and pumping enough fuel to the injectors.

  3. Fuel Injectors: Those little buggers can cause trouble if they're not working right or if they're clogged. Get 'em checked or replaced if needed.

  4. Spark Plugs and Ignition: Don't forget to inspect your spark plugs, ignition coils, and module. Faulty ignition stuff can make starting a nightmare.

  5. Fuel Pressure Regulator: This thing helps keep fuel pressure stable. Make sure it's doing its job right.

  6. Electrical Connections: Take a look at all those wires and connections related to fuel and ignition. Make sure they're clean and snug.
    Boat engines can be finicky. Consider taking it to a boat mechanic.
 
Thanks for the info. I have a boat mechanic scheduled but summer is more than half over where I live in CO. Everyone's too busy these days.
 

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