5.0 Backfiring

[Mark Schallip]

I have a 240 Sundancer 1999 with a 5.0 efi. with a Mercruiser Alpha 1 outdrive. The problem is backfiring. Not all the time but every so often. The more people you have in the boat the worse it is. I have replaced disc cap, rotor, spark plugs, spark plug wires, pick up in dust, fuel filter, fuel pump and heads. still does it. This is getting expensive and is frustrating. Does anyone have any suggestions?

 

[SeaRide]

Mark,

I had a similar problem years ago as did another member. Have a look at this link and see if it matches up with your issue.

http://clubsearay.com/index.php?threads/resolved-tach-jumping-boat-backfiring-under-load.84388/

 

[scoflaw]

Do a leakdown, bad valves can do that.

 

[Handsome Transom]

Plus one on sticking valves exhaust valve deposits from running too lean or old gas resulting in a carboned up valve and seat

 

[Mark Schallip]

Sea Ride I posted an answer on the http you posted earlier. THANK YOU SO MUCH!! The switch cured the problem. We had a great summer of boating. Due to computer and log in issues, I have not answered earlier. My mechanic thinks I am a genious. Thanks again.
Mark