350 MAG MPI surges & backfires

[Neillson]

I have a 2003 EbbTide 2400 powered by a 350 MAG MPI, Alpha Drive with only 54 hours on it. I bought it new. At about 51 hours I was pulling a tube at 3000 RPM when the engine suddenly started surging and then bogged down. Increasing the throttle caused a backfire. It will run up to about 1800 RPM under load before bogging down again. In neutral it will run all the way up to WOT.<br />I replaced the water/fuel separator and added dry gas to the tank. Didn't help.<br />Dealer found low fuel pump pressure and fluttering on his gauge. The dealer replaced the fuel pump. Same symptoms. He diagnosed a stuck anti-siphon valve. Removed ball from valve until he can get a new one ordered. <br />Ran fine (except for one or two burps) for about 3 hours and then same symptoms returned.<br />He is referring to Mercruiser. Any ideas while I wait??

 

[hondon]

Re: 350 MAG MPI surges & backfires

Try replacing the in line fuel filter if you are equipped with the boost pump as I believe you are.How did that fuel sample from the water separator look?

 

[Neillson]

Re: 350 MAG MPI surges & backfires

There is no in-line filter only the water separator. Since I wrote the question above, I replaced all the fuel with fresh fuel. I took it out and it ran until it reached 180 degrees and the same symptoms appeared. This time it would not even run at idle and I had to be towed back.<br />I never thought to look at what was in the old water separator.<br />The mechanic is supposed to try again tomorrow (Monday). <br />I have read a lot of reports of Mercruisers with this same or very similar problem. I can't find anything in their reports on it.<br />Thanks for any help I can get.

 

[Neillson]

Re: 350 MAG MPI surges & backfires

Problem solved. Mechanic replaced anti-siphon valve and fuel pickup tube (It is all one unit). Ran fine for about one hour and then quit again. Connected portable fuel tank directly into fuel line into fuel pump and it ran about four gallons out of the can with no problem. Pulled the new anti-siphon valve and pickup hose and found it had a screen in it. The screen was clogged with what looked like a small chunk of silicone sealing compound. Probably fell into tank when installing fittings at EbbTide factory. <br />Pulled screen out of end of fuel pickup hose and it has run perfectly for ten+ hours. <br />It may be my imagination but it seems to run better than ever. <br />Mechanic said he had never seen a fuel pickup with a screen in it since the water/gas separator filter would trap any junk coming from the tank no screen is needed.<br />Thanks to a persistent mechanic I'm up and running again. <br />Thanks to all who helped with suggestions on this forum.