Fuel in Exhaust on Mercruiser 454 MPI

B

BornToBoat

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I have twin mercruiser 454 MPI engines in a 1997 Searay Sundancer 330. Both engines were rebuilt 3 seasons ago, and have always run fine.

This season the starboard engine has a heavy fuel smell, and noticeable fuel in the exhaust. The mechanic hooked it up to a computer and says all the readings are normal. He tried swapping out the ECM and the problem persists.

He has already replaced the mechanical fuel pump and the electric fuel pump. He has also verified that the sensors are working.

Any additional ideas will be greatly appreciated.
 
Rob......You say fuel in the exhaust ?? Is it coming out the thru-hull exhaust....and you notice it on the water ???....or is it in the manifolds ??

Do your motors have fuel coolers in the raw water system ??
 
Don,

It's coming out thru the thru-hull, and I can see it in the water. No smell at all in the engine compartment.

I don't know if I have fuel coolers in the raw water system. That's an interesting thought. How can I tell if I have that?
 
Rob.....follow the fuel line from one of the fuel tank.....it should go to a fuel filter ....then ( if you have coolers ) to a fuel cooler....then to the high pressure pump. They look like tranny/oil coolers.......Its a round tube cut into the raw water system.....with fuel line fittings on them.

I have them on my engines.....and I had them rebuilt....when I did my cooling systems over.......about 3 seasons ago.

They are needed to prevent vapor lock.

Also ......are you sure its fuel ????...not tranny fluid ???......I had the same symptom.....with a shine in the water comming out of my exhaust thru hull......turned out to be the tranny cooler had a pin hole.

Good Luck
 
Don,

Thanks for the details. It's definitely gasoline. Very noticeable smell.

I can't get to the boat till this weekend, but I'll ask the mechanic to check the fuel coolers if I have them.
 
Don, you win the prize. The mechanic called me earlier today and told me it is the fuel cooler.
 
Rob......It was a common problem........The reason why the engine still runs is because the fuel pressure is higher ( greater ) then the raw water pressure.......and the fuel is FORCED into the raw water system....and out the exhaust.
If it was reversed pressure......you would ingest water.

The next obstical will be to find someone who is willing to repair it......most shops refuse to accept the liability of repairing FUEL COOLERS.........and they are no longer available from Merc.
 
my mechanic found a source in fon dulac that has 10. mine should be here tomorrow
 
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