Rough running Volvo 8.1 randomly struggles for power.

Aqua_Aura

Took the boat out for the first time this year and seems to have been running fine all winter as I start it occasionally. When we left the dock it seemed to have a rough idle. To put it simple when I add power it sometimes is fine but sometimes it will drop power and struggle. I am thinking maybe fuel filter and maybe bad fuel from sitting all winter. The fuel in it is ethanol free and I think I had additive in it. 

Any thoughts? 

aero3113

I would start with the fuel filter. When is the last time you a full tune up has been done?

Aqua_Aura

New plugs have about 40 hours or less. New oil and fuel filter last May. I have a fuel filter I'll put on this weekend just to eliminate any issues. 

GMSLITHO

Water separator 

Aqua_Aura

I guess I should probably keep my spare filters on the boat 😬. I've had one at my house and I don't know why I didn't keep it on the boat. 

Liberty44140

How old is the cap and rotor? Fuel filters, cap and rotor are an easy first step. 

Willhound

Yeah, I keep a couple of water separators on the boat all the time. Cheap insurance especially if on a trip and you get fuel from an unknown source. Keep a small container or tube of plumbers silicone grease too and lube the filter seal so it doesn't weld itself to the housing. First time I changed one I had to pull the whole mount off and put it in a vice. I've also changed my rotor and cap and kept the old ones as spares, they were a little worn but still usable. Again, not expensive. 

Aqua_Aura

This is a 2007 8.1 so it's fuel injected. I am gonna put seafoam in the filter per their directions to clean the fuel system particularly the injectors. I think they are fine but might as well. If the injected was clogged I don't think the power changes would be random. 

I'll definitely put some grease on the seal, good idea. 

aero3113

Keep a pair of these on the boat. They will be your best friend when you go to change filters.

https://www.harborfreight.com/oil-filter-pliers-61477.html

PickleRick

If you're not 100% you stabilized the fuel id check there.  Un stabilized fuel from the pump has a shelf life averaging 30 days

Aqua_Aura

Speaking of bad fuel I had a few gallons of fuel in a plastic boat tank that was atleast 6 years old. Needed to mow my lawn and didn't want to go to the store so I figured I would give that a try. It ran fine but the mower is carbureted and I'm sure less picky then a fuel injected Volvo.

PickleRick

Actually the efi system can pass varnish or lower(aged) octane better than a carb.  You have some 45 to 55 psi pushing it vs the compression pulled carb.  Fuel is also better atomized in efi vs carb. 

Willhound

PickleRick said:

Actually the efi system can pass varnish or lower(aged) octane better than a carb.  You have some 45 to 55 psi pushing it vs the compression pulled carb.  Fuel is also better atomized in efi vs carb. 

Well yeah, but it'll still make it run like crap.

PickleRick

Willhound said:

PickleRick said:

Actually the efi system can pass varnish or lower(aged) octane better than a carb.  You have some 45 to 55 psi pushing it vs the compression pulled carb.  Fuel is also better atomized in efi vs carb. 

Well yeah, but it'll still make it run like crap.

I agree.  Bad gas pays for all my toys.  Our fuel in the USA is so bad Stihl has to use a different electric solenoid on their m tronic carbs in the USA than whats used in the rest of the world.

German engineers had to be sent our bad gas for research.

Aqua_Aura

Lawnmower I am sure has much less load than the boat which probably makes it a little easier to pass bad gas 😏

Aqua_Aura

I was looking at filters to get another spare since I'm gonna use mine and was wondering if Sierra is better worse or same as Volvo? The equivalent Sierra filter is half the cost. 

Willhound

Oh boy. You opened a can of worms there. Most of us are Mercruiser/Quicksilver but there's always a debate about OEM vs aftermarket.  But for my 2 cents I beleive Sierra to be probably the best non OEM and use them myself. I use the Mercruiser oil filters but the Sierra water separators since I change mine at least every year, sometimes twice.

Aqua_Aura

Well let me add some more to this can of worms. I am a Wix/Napa filter person myself and I did see that they seem to make an equivalent as well... Anyone..... Anyone. 

Hopefully we can all agree not to use Fram. 

Willhound

   you might find a Fram guy here. Any big name is probably ok. Look at it this way. So many things are mass produced overseas these days and different companies put their name on them. It's all marketing and distribution line.

Aqua_Aura

Yeah no one seems to make their parts anymore just put their name on things. I have products manufactured in China and sent to the US and I am pretty sure my name brand competitors probably use the same factories.

One thing for sure though is that even though they are in the same factory the factories will make it to the brand owners specifications. 

PickleRick

Another vote for wix

3hp chainsaw with 18inch bar chewing through hard wood may equal a 260 hp engine pushing a 4000 lbs boat in load vs hp.


Low octane fuel can damage both.

Aqua_Aura

Definitely bad fuel, I took the regulator off so I could see the fuel and it has water. I'll need to bring the filter wrench down next time and pull the filter. I did put additive in it yesterday and today it ran much better, I kept the power low and just went for a cruise around for a few hours.  I'll add new fuel once it runs down a bit more. 

aero3113

Check the o-ring on your fuel cap. Make sure it’s not missing or breaking up.

Aqua_Aura

It's new just checked it yesterday. Also it's on the side of the boat so it would be very difficult for anything to get in. I am gonna call the last marina I fueled at before winter and see if their fuel is ethanol free. Everywhere on the river generally is but maybe they're not. 

Willhound

Even if they are ethanol free it's possible to have water in their tanks if they get low enough. They should be testing for water daily. A lot of places allow their tanks to drain down before winter.