Engine problem unresolved need to find closure.

[StarCraft 2012]

Good morning, new to this forum glad to see there is a place to discuss
2012 4.3 MPI alpha 1
on river couple weeks ago, after a few minutes of running the engine began backfiring and lost power. this is at high RPM and at idle where it would hunt and surge all the way back to dock even at very low speed.
took to mechanic he replaced fuel filter, plugs, and said he cleaned the fuel regulator?!
he stated the pump pressure was good.
when i took it back out for a test cruise after 15 it did same thing. in a last ditch effort I loosened the fuel cap (Vapor lock Maybe)
after couple of minutes it started running normal again. I could not recreate the problem after 45 minutes going back and forth between full throttle and low speed all seemed good.

One question in my head is where is the Fuel tank vent? cap or a breather somewhere else.
am i looking in the right place for the issue?

Thanks
MM

 

[makomark]

If the tank vent is clogged, the pump has a hard time supplying enough fuel..the vent should be outside the hull...usually close to the fill.
Did the mechanic run the e line u Der load when he checked the pressure??

 

[StarCraft 2012]

If the tank vent is clogged, the pump has a hard time supplying enough fuel..the vent should be outside the hull...usually close to the fill.
Did the mechanic run the e line u Der load when he checked the pressure

I have seen nothing that resembles any fittings near the fill that's why I assumed the fuel cap might be the vent.
Test under load "yes" if that means in gear with muffs on.....

Thank you
MM

 

[makomark]

Running the engine on the muffs in NOT the way to test the fuel pressure.

Never seen the vent built into the fill cap but it is possible...if you can se the top of the fuel tank, there should be two hoses...the 1.5" ID (fat) one is the fill hose...the 5/8" ID (skinny) one is for the vent .... sometimes, they will run to the opposite side of the hull (from the filler) or to the transom...

you can google < boat fuel tank vent > to get an idea of what most builders use....there are multiple styles...

 

[kghost]

Running the engine on the muffs in NOT the way to test the fuel pressure.

Never seen the vent built into the fill cap but it is possible...if you can se the top of the fuel tank, there should be two hoses...the 1.5" ID (fat) one is the fill hose...the 5/8" ID (skinny) one is for the vent .... sometimes, they will run to the opposite side of the hull (from the filler) or to the transom...

you can google < boat fuel tank vent > to get an idea of what most builders use....there are multiple styles...

Mark, 4.3 MPI..... I am not sure if they vent the tank the same as Carbed

 

[StarCraft 2012]

Running the engine on the muffs in NOT the way to test the fuel pressure.

Never seen the vent built into the fill cap but it is possible...if you can se the top of the fuel tank, there should be two hoses...the 1.5" ID (fat) one is the fill hose...the 5/8" ID (skinny) one is for the vent .... sometimes, they will run to the opposite side of the hull (from the filler) or to the transom...

you can google < boat fuel tank vent > to get an idea of what most builders use....there are multiple styles...

Not familiar with methods to troubleshoot an engine or systems in a boat.
I am basically on a witch hunt because the loosening of the gas cap and the boat working better coincided on this occasion.
intermittent problems are the worse ever....

they must have built the boat around the tank cant see much of it I do appreciate your feedback and will dig a little deeper on the weekend.
will check for the things you mentioned.

Thank you
MM

 

[makomark]

Mirrors, flashlights, and cell phones help in the inspection department.

Kghost - I am all for enlightenment is something has changed...the EPA will strike, again, I am sure...I am not aware of any changes to fuel tank vents for EFI...

 

[kghost]

Mirrors, flashlights, and cell phones help in the inspection department.

Kghost - I am all for enlightenment is something has changed...the EPA will strike, again, I am sure...I am not aware of any changes to fuel tank vents for EFI...

Ok, I wasnt sure you saw that. I personally have no real MPI/EFI system experience...

Every boat I work on still run Carbs......

 

[makomark]

Its a lot easier with them....

 

[louc]

Yep I have no intention of getting rid of my old carbed boat, I grew up with cars with carbs (Rochester, Autolite, Solex) so I’m familiar with them.
Not sure when this started but newer boats have a vapor recovery system like cars have had for years, they are not simply vented to the atmosphere like old boats are. This system uses a charcoal canister like in your car. I’d also check the anti siphon valve on the fuel tank.

 

[StarCraft 2012]

Yep I have no intention of getting rid of my old carbed boat, I grew up with cars with carbs (Rochester, Autolite, Solex) so I’m familiar with them.
Not sure when this started but newer boats have a vapor recovery system like cars have had for years, they are not simply vented to the atmosphere like old boats are. This system uses a charcoal canister like in your car. I’d also check the anti siphon valve on the fuel tank.

Thanks to the both of you for your input!
Hope to find something to make me trust my boat again.....

MM

 

[sandkicker]

I had a chat several years ago with engineers @ Mercruiser... Engine life @ WOT measured in 10s of hours. Life @ 80% or less of WOT measured in thousands... especially if in fresh water or FWC in salt.

 

[makomark]

Yep I have no intention of getting rid of my old carbed boat, I grew up with cars with carbs (Rochester, Autolite, Solex) so I’m familiar with them.
Not sure when this started but newer boats have a vapor recovery system like cars have had for years, they are not simply vented to the atmosphere like old boats are. This system uses a charcoal canister like in your car. I’d also check the anti siphon valve on the fuel tank.

Thanks Lou.

from the little big of digging I did, looks like it started in 2013 and there isn't a lot of detail that easy to find...I guess the good part is the burden appears to fall on the hull guys and not the engine guys...either way the idea of another vapor cannister inside of a hull isn't my cup of tea...my guess is they are still figuring out a compliance approach for after hull delivery...

 

[StarCraft 2012]

Ok, I wasnt sure you saw that. I personally have no real MPI/EFI system experience...

Every boat I work on still run Carbs......

Good afternoon, after some digging and testing I did find the vent it actually comes back up to the fill port where there is a small open vent behind the cap. the gas cap does have a screen and vents through the cap. the cap has an O-ring which was compressed and allowed the cap to close down tight against the base choking off the air.
New O-ring and no issues since.

thanks for the help.
MM

 

[kghost]

Great find, 99% of boats have a separate vent hose to a spearate vent port.

Yours is in the cap.....

Personally, I would look into a separate vent and the oring issue will be a thing of the past, permenately!

This is a high qualty vent. I have this style on my boat.

Thru-Hull Vent | West Marine

Check out our Thru-Hull Vent and more from West Marine!

www.westmarine.com