383 FWC - Strong gas smell while idling, lower compression in one cyl. Any thoughts?

[jase34242]

Going to start by saying I know I should have addressed this when it was first put in, 5 years ago I didn't realize what was going on.

The story is, bought a boat, the motor in it went south the 2nd weekend of ownership. Instead of rebuilding I decided to go with a reman directly from mercruiser, everyone said get the 383 FWC, so I did.

A professional mercruiser shop put it in, and replaced everything that was needed (20k!).

The same day they signed off that it was complete a friend stepped on the boat and told me something was wrong, but I was too high on life to listen.

For the past 4 or 5 years it's always had a strong gas smell at the dock.

Mechanics have always done the yearly work on it (I change the oil 2 times a year and other small things, in FL).

Only just this past year did a mechanic say "I don't like how it sounds and it's not burning some fuel". He did a compression check and one out of 8 cyl (the stbd rear) come up with 90 psi while the others are just over 150.

Kicking myself hard over here because I had the extended warranty but just wasn't paying attention enough to know there was/is an issue.

If the spark plug is replaced in that cyl. the motor does "Sound" smoother for a time, and the gas smell does go away, but only for a short amount of time..

Any thoughts ? I'm in South Florida where it's not easy to find a certified Merc. mechanic and half of the ones that are, still don't know what they are doing around an I/O. I had one that was going to come investigate and he suddenly moved to mexico.

Any help is appreciated. I have searched high and low hoping there's a recall and contacted Mercury, but have not heard anything back from them.

Thank you!

 

[tpenfield]

If you are going to do your own diagnostic work, start by ruling things out.

My thoughts . . .

Gasoline leak . . . check to see if the fuel system is leaking.

Low compression . . . Do a cylinder leak test to determine the source of the lower compression. General possibilities are intake valve, exhaust valve, head gasket, piston rings.

Do you get an oil/gas sheen on the water while idling at the dock? That would be indicative of un-burned fuel. If not, the gasoline smell make be due to a leak (somewhere ).

Any warranty left on the engine? That tends to be a difficult route anyway.

Have you mentioned the gas smell issue to the mechanics who have worked on it?

Does the engine generally perform as expected (power, boat speed, etc)?

 

[alldodge]

Sorry to say but getting a Merc reman doesn't mean you got a good motor. My Buddy put 2 of them in and both had issues, this why this time we rebuilt it. As Ted said do a leak down test to find out what the problem is

 

[Lou C]

I’d be looking for either a plug not firing or a fuel injector leaking…this is an EFI motor?

 

[Scott06]

90 psi is a dead cylinder do the leakdown test to verify where it is going.

 

[Scott Danforth]

Leaking injector will take out a cylinder and have a gas smell

In addition to Ted's list. Pull the injectors and have them tested

If you keep it in the water, check the exhaust manifold. Even the dry joint manifolds can fail

 

[stresspoint]

i will also go with a bleeding injector that has now taken out an intake valve.

you may be lucky and just have a very bad pitted valve seat "however" that would depend on how long ago you started to loose compression.

 

[Lou C]

Might want to check static water line height if you find rusted exhaust valves on any of the cyls. Should be at least 13”.

 

[nola mike]

Did I miss the part where this is a fi engine?

 

[tank1949]

Going to start by saying I know I should have addressed this when it was first put in, 5 years ago I didn't realize what was going on.

The story is, bought a boat, the motor in it went south the 2nd weekend of ownership. Instead of rebuilding I decided to go with a reman directly from mercruiser, everyone said get the 383 FWC, so I did.

A professional mercruiser shop put it in, and replaced everything that was needed (20k!).

The same day they signed off that it was complete a friend stepped on the boat and told me something was wrong, but I was too high on life to listen.

For the past 4 or 5 years it's always had a strong gas smell at the dock.

Mechanics have always done the yearly work on it (I change the oil 2 times a year and other small things, in FL).

Only just this past year did a mechanic say "I don't like how it sounds and it's not burning some fuel". He did a compression check and one out of 8 cyl (the stbd rear) come up with 90 psi while the others are just over 150.

Kicking myself hard over here because I had the extended warranty but just wasn't paying attention enough to know there was/is an issue.

If the spark plug is replaced in that cyl. the motor does "Sound" smoother for a time, and the gas smell does go away, but only for a short amount of time..

Any thoughts ? I'm in South Florida where it's not easy to find a certified Merc. mechanic and half of the ones that are, still don't know what they are doing around an I/O. I had one that was going to come investigate and he suddenly moved to mexico.

Any help is appreciated. I have searched high and low hoping there's a recall and contacted Mercury, but have not heard anything back from them.

Thank you!

look for a cracked hose. or inside carb when running.

 

[QBhoy]

If this is the 383 that’s an mpi engine…the obvious thing to my mind is that the low compression might be a result of unburnt fuel conditions at that cylinder…caused by the now infamously terrible distributor cap.