Rough running starboard

N

Nmor830

Member
Sep 12, 2016
90
Channel Islands
Boat Info
2008 340 Sundancer
Engines
8.1l Mercruisers
hello all,
My 2008 sundancer starboard starting misfiring badly. Won’t go over 2500 rpm. I thought it might be bad fuel but port runs fine and this is the second time it happened. First time I ran some injector cleaner though the tank and it cleared up the problem. Always try the simplest thing first. Now it’s starting again. Before I start calling Mercrusier does anyone know the part # for injectors for this model and year engine? Also your opinions on cleaning old ones verses replacing with new. I’ve spoken to several mechanics and they all suspect the injectors. Any advice and opinions greatly appreciated.
Thanks,
Nick
 
Check the fuel pressure regulator for paint chips (from the cool fuel canister) - or swap from port to stbd. And, yes, clean the injectors - most injector shops charge about $20/per injector. When is the last time you changed/inspected the two filters inside the cool fuel unit?
 
Lazy Daze said:
Check the fuel pressure regulator for paint chips (from the cool fuel canister) - or swap from port to stbd. And, yes, clean the injectors - most injector shops charge about $20/per injector. When is the last time you changed/inspected the two filters inside the cool fuel unit?
Click to expand...
 
Have not checked the filters on the cool fuel unit but will do. I’m going to go through the whole fuel system.
Thank you
 
Any alarms on the boat - make sure you are not in "guardian" mode for some reason.
Next, you should start with simple items - check plugs and wires - make sure something did not disconnect.

I don't think a injector cleaner will work well running it through the tank. Normally on my cars I add it when there is about 10-12 gallons remaining for proper concentration - that will not happen with our tanks.

Also, be aware of the Cool Fuel 3 (CF3) issues. Merc knows about a delamination problem inside some CF3 units. When the paint flakes it clogs the injectors. The word is there is no official recall but I do know people who had the parts replaced my merc for free last year. To do this you must go through a merc dealer to get the parts authorized and pay the dealer for labor.

-Kevin
 
saopm said:
My first step would be to check the plugs. Should help you narrow down which cylinder has the issue.
Click to expand...

Absolutely! 8.1's are known to go through the plugs. I had same issue a few years back and plugs fixed it. I also changed the wires for good measure.

If it's the CF3 unit and you have paint chips I highly doubt injector cleaner will help. You'll need to remove and either replace or have the existing ones cleaned. Be aware that Mercruiser has a TSB on the CF3 units and if your boat falls within the serial number range they'll give you free injectors, pump and fuel rail. You'll be responsible for labor to get them installed though.
 
Thanks for all the advise. The CF filters look clean but changed them out anyway. Going to pull the plugs in next few days to check condition. One thing I’m noticing is RPM fluctuating by 100-150 at idel and through out higher ranges?
 
I would still start with the plugs it is simple but note the center plugs conditions near the elbows.

Also how old are the manifolds. As stated before you could also be getting some leak back of water causing the variable RPMs through ranges and the rough idle.

-Kevin
 
Nmor830 said:
Thanks for all the advise. The CF filters look clean but changed them out anyway
Click to expand...

The paint chip issue happens downstream of the filters. That’s why the injectors get clogged. I’m not saying that CF3 is your problem, but just to clarify.
 
KevinC said:
I would still start with the plugs it is simple but note the center plugs conditions near the elbows.

Also how old are the manifolds. As stated before you could also be getting some leak back of water causing the variable RPMs through ranges and the rough idle.

-Kevin
Click to expand...
Manifolds are original as far as I can tell. I’m the 3rd. Owner but from the looks of things they don’t look like they have been changed.
Thanks
 
Thanks kind of what I thought. I saw a video where they took the cf3 apart and cleaned all the paint out scraping, etc. has anyone had experience doing this? At over 1k plus labor it seems doing this would be a less expensive option for a perfectly good working pump if all the paint and crud was removed. Just a thought.
Thanks
 
Nmor830 said:
Manifolds are original as far as I can tell. I’m the 3rd. Owner but from the looks of things they don’t look like they have been changed.
Thanks
Click to expand...

That would put them at 10 years old and well beyond salt water life expectancy and even near end of life for fresh water without inspection. An inspection would be prudent even without a problem not knowing if or when they may have been replaced. A previous owner may have sold the boat knowing that a major maintenance item was coming up.

Regardless of the problem you are having if these are really that old and you are in salt water I would still (but immediately) look to the center plugs under the elbows first as they are more likely to get a leak from a failed gasket and work outward.

Pull them, mark the engine and the cylinder and look for rust / evidence of salt. Look for differences in plug condition. You might even need to slightly "taste" it for a salty flavor. If you show rust or salt on any of the plugs go straight to pull the elbow and inspect the manifolds and have them replaced if needed.

Do not risk hydro-locking an engine to escape a little bit of maintenance - especially when already facing a problem. Right now an inspection may be a couple hundred dollars labor and parts, replacing manifolds may be a few thousand for both engines (required maintenance) but a blown engine will put your around 20K (each).

-Kevin
 
Stick a camera probe in the spark plug holes. You may see water or salt encrustation. My mechanic said if the manifold is leaking a little it can make the engine run rough at slower RPMs. Then with higher RPMs, there is higher than normal amounts of steam in the exhaust.
 
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