496 Ho question - fuel leak?
 

I have a 496 ho thru hull exhaust, when idling the starboard side exhaust is leaving a sheen of fuel on the water. So far the mechanic has replaced the regulator, fuel pump module, pulled fuel injectors and cleaned. Any ideas why this is still happening?

How does it run ?

I just pulled a boat I worked on for the same problem. "Fuel or oil is leaking cause of the sheen on the water !"

I just greased everything in the back....and that was what it was. Doh !

the oil cooler may be leaking oil into the cooling water from the sea pump.is the engine oil level going down?

Possibly an ECT issue. ECM is enrichening the fuel circuit because it believes the engine is still cold. A diagnostic run with G3 will help resolve the issue, otherwise have your mechanic run some diagnostics with his other Mercruiser diagnostic program if not G3 compatable. Many sensors on that engine package are related and utilize the same circuitry to send the ECM info, so it may be a simple sensor replacement, or it may be more difficult. Good luck.

Never mind then.... Extra grease can do that too, you must've really slathered it on.

What year is the engine? Better yet, what is the engine serial number?
What do the spark plugs look like?
What fuel pressure are you seeing on the tester gauge?
Has the engine been scanned on a scan tool?

It actually runs good

No the engine oil level hasn't changed

Mine isn't grease, it is coming out of my exhaust

It's a 2005, don't have serial number with me. Spark plugs look good. Fuel pressure is normal, and I asked mechanic to scan tonight.

these engines a very sensitive to spark plugs - change them and do not touch the gap. AC delco or NGK is the only plug I would use for these 496. Spark plug wires and coils need to be checked as well.

Engine serial number is a must and so is an engine scan - what temps is this engine running at especially at idle ?

Is the T stat stuck open ?

Coolant temp sensor (possible ) plus you can ohm test them to see if they are good or not.

The engine needs to be scanned and monitor engine temps - temp gauges at the dash can be off 10 % sometimes. Read temps with the scan tool running on the lake thru out RPMs 160 degrees or bit higher.

Dirty flame arrestor is another huge deal for the 496 running rich. They need to be deep cleaned bare min once a year - when was the last time you clean the heck out of it.

Just had a 2006 formula that the flame arrestor was never cleaned - talk about rich and wet spark plugs - about chocked me to death running it on the water hose.

I would start with cleaning the heck out of the flame arrestor and changing all the spark plugs. Test wires and coils then see how that goes. Make sure your throttle body and throttle plate is very clean as well. Again move on from there especially with a complete scan by someone who knows how to read it. Many think just because there is no fault codes that all is great with the engine. 100 % wrong