Misfiring MerCruiser 4.3LX

[Simon Wootton]

Running this weekend for 1.5 hours at around 3200rpm no problems - suddenly the motor lost power but didn't die. Applying more throttle to get her back on the plane just caused a lot of popping and banging - backfiring I suppose? I managed to get back OK as the motor ran as smooth as silk so long as revs were kept around 2000. A couple of times I attempted to get backon the plane with the same result of bad misfiring.<br />Once back at the jetty I revved her in neutral and it span clean as a whistle. Any ideas where to go first?<br /><br />One other thing possibly totally unrelated - the oil level always looks good and is never milky, but I always get a little water on the underside of the oilf filler cap when I look. The boat is left on a mooring and I start it up at least one a week. Do I have to worry about this too?<br /><br />Thanks.

 

[akriverrat]

Re: Misfiring MerCruiser 4.3LX

water on fill cap fairly normal. other problem could be fuel or ignition. or something else,more details would help. fuel-check filter/s for water and plugging. check fuel lines, tank pickup, and antisyphon valves. weak fuel pump. clean flame arrestor and be sure choke is opening. ignition-check, adjust, or replace points, cap, rotor.

 

[Simon Wootton]

Re: Misfiring MerCruiser 4.3LX

Thanks - I'm going the fuel filter / system etc. route first!

 

[jjpetrusha]

Re: Misfiring MerCruiser 4.3LX

just bought 19' sea ray w/ 4.3 v6 mercruiser<br />Am having the exact same problem.sounds great w/ no load . But major back firing and will not get on plane after it gets hot<br />I filled it up w/ 93 oct fuel could only get 5 gal. in it b4 full.<br />am going to try heet or training the tank<br />let me know what you find<br />thanks jon

 

[Simon Wootton]

Re: Misfiring MerCruiser 4.3LX

Jon - so far all I can find is that my fuel filter is absolutely clean. I understand that on a 4.3LX like mine, there is a low oil pressure switch that acts directly on the electric fuel pump. My next shot is to jump out the wires form the switch - my oil pressure is OK at the gauge - and see if the problem re-occurs. if it does then I guess I need a new switch - if not I'm going to check the carb out for loose dirt.<br /><br />Your problem does sound similar Jon. The switch on mine is at the lower port side of the engine - two purple wires emerge from there. May be worth a check?<br /><br />Good luck!<br />Simon