Gas leaking from Exhaust???

This past weekend I noticed gas leaking into the water coming over the swim platform on my 99 Santera when the boat was running in neutral or idle? Quite a bit of gas actually. In the slip there was about a 6' ring of gas behind the boat. Because it was coming over the swim deck I figure it is coming from the exhaust? Can anyone tell me what might cause this or what could be done to fix it. It's fuel injected and I'm running No Ethanol Premium gas. Any tips or advice would be very much appreciated. Thanks!

If this only happened once, I would bet that you spilled gas somewhere. If it happens every time, then you have a problem.

A 6' ring of gas is not very much. Gas/oil will generally spread out (and still be visible) at 5 microns thick.

3.24 meters^2 x 5 microns = .00000162 meters^3

Which is equivalent to .05 of an oz. Check the engine for any places where you might have leaking gas or oil. IMHO, a leak is more likely than unburnt fuel out of the exhaust.

It was happening all weekend when the boat was running or in idle. The weekend before I noticed a strong gas odor. I could see gas coming up between the swim platform and the hull in the "wash" of the exhaust. There was a very strong gas odor coming from behind the boat, but none in the engine compartment. Which leads me to believe it's coming out the exhaust. What could cause unburnt fuel to come out the exhaust?

If you had a decent amount of gas coming out the exhaust, I would think it wouldn't be running right.

It sounds like a pretty good mystery to me. How many bilge pumps do you have?
Mine bilges out the starboard side right in front of the driver's seat. Is yours the same or do you have a bilge that pumps out the back?

Only reason I ask is if it's possible that it's coming-out of the bilge, that opens-up a lot more possibilities.

Places fuel can come from... (just brainstorming here so bear with me.)
Leaking filler-neck. (Would most-likely end-up in the bilge or on the floor of the boat.)
Leaking fuel tank. (Same as the filler-neck.)
Sloshing out of the tank-vent or fill cap. (Would end-up in the water at the back of the boat.)
Fuel line between tank and engine. (Bilge.)
Anywere else before it gets to the cylinders and it should end-up in the bilge.

I guess it's possible that it could be running really rich and making-it all the way into the exhaust, but I just don't see how that could happen without you noticing a big performance problem. If you had a couple dead spark-plugs it could happen too, but again, you would definatey notice that too.

Does it still do it after its been running for a while or just when you first start it up (or start-up after sitting for a few min)?

Have you tried running it on the hose to see if you can find fuel leaking from somewhere other than the exhaust?

There are a limited amount of places that it could make-it into the water from inside the boat.
Exhaust
Filler Cap
Vent
Hole in the hull somewhere... But if this was the case, water leaking-in would prevent any fuel from getting out. Unless it was leaking onto the hull then washing-off into the water when you put it in. But if that was the case, eventually the water would clean-off all the fuel and it would quit...

Hmmm...

The only time gas is leaking is when the boat is running so I don't think it could be anything to do with the bilge or leaking anywhere from inside. It seems to be running perfect idling and underway. I will take a look at the spark plugs. I haven't had it connected to a hose yet, but that will be my next step.

Just trying to help brainstorm here.... I would also check your transmission fluid level. The oil coolers are designed so that transmission fluid SHOULD leak out before water can leak in. It doesn't always work that way, but that is how they are designed. That would then end up in your coolant system and eventually find its way out the exhaust. Might be a long shot but I'd try there...

The other thing that you are missing is that so far, everything you have described as while the engine is running, is also while the fuel-pump is running. There could be a leaky injector or something else still. That would get it in the bilge but I'm still not sure how it would get out. Does the boat leak or does your bilge rarely have to be run?

There is a strong odor of gasoline, but ONLY from behind the boat. When I open the engine hatch, there is NO odor of a gas smell. Because of the odor, I don't think it could be transmission. If it was leaking somewhere "internally", I think I could smell it stronger when I open the engine hatch.

The boat does take on a little water when sitting in a slip overnight. Bilge runs for about 30 seconds each morning after a night of setting.

I've done some Google searches throughout the day for gas leaking from exhaust and haven't really found anything even on cars. Some people say it means it could be running rich, but I'm not sure how you fix that on a fuel injected engine. I'm really not much of a mechanic. I hope it's not something super major.

The engine just hit 190 hours. I bought the boat at the beginning of last season with 100 hours and it's a 1999. So it sat most of it's life. I'm sure there are seals and gaskets that have began to become brittle and crack from setting for so long...

The way the transmission cooler works, it would not be leaking into the boat. It would be leaking into the fresh-water supply which would then be dumped out the exhaust.

I do agree though, it would not smell like gas.

Your bilge use after a night of sitting on the water sounds VERY minor. Doesn't sound like gas is able to make it out of your bilge and into the water.

I'm stumped. Hopefully someone else can chime in with ideas....

I really appreciate all the advice and help from everyone!

Pull the plugs. Verify the plug wires are on right.

I just can't imagine that it wouldn't run like crap with that much (enough to smell) un-burned fuel going-out the exhaust...

I'm stumped too...

I've contacted the MasterCraft dealer / tech (the only inboard dealer in the area at the lake the boat is on) and he sounded stumped as well. I told him to go ahead and get the boat and check it out. Since the boat is 3.5 hours away at the lake I use it on, I hate to spend a whole weekend diagnosing a problem instead of enjoying being on the water.... I'll post what the outcome is once he's had a chance to look at it. Maybe he will find that it actually is running like crap because of plugs not firing, but seemed normal to me??? Keeping my fingers crossed it's nothing too major, but rather just an adjustment. - Thanks Again!!!!

I had the same problem on my 1999 Supra Santera. The high pressure fuel pump is water cooled. There was a recall on it. It was supposed to be bypassed. Yours, like mine, must not have been done. Now you have a pin sized hole in your high pressure fuel pump, causing gas to leak into the exhaust. You have to replace the high pressure fuel pump, and bypass the water cooling canister. Good luck if you haven't already figured it out.

Waiting for your response 89conbrio as to whether you solved your problem based on advice from " mellis" on previous post.
Pls advise