4.3L MPI surging when trying to rev or under load

[sebbi69]

I have a approx 2007 Mercruiser 4.3L MPI (EFI) which has done 195 hours. It has been going great but just recently when you try and rev it the engine it surges badly like it is running out of fuel. I have replaced the fuel filter and now replaced the complete housing with a RYCO water separator filter unit so I can see if there is any water in it and see that there is fuel in the system. Neither changed anything. I have run the fuel hose into a glass bottle so I can see the fuel pump is working and yes it is pumping fuel. The motor idles fine but is pretty much not usable at the moment.

I have had a boat mechanic look at it and they thought they had the issue fixed by tightening the fuel input line clamp. That seemed OK for a while but not any more. I have also replaced the complete fuel hose and am now running it out of a small fuel can with brand new fuel. Still the same.

If you watch the video (link below) you can see what appears to be bubbles in the bowl of the fuel filter. Does this seem correct?

Thanks for your time.

https://1drv.ms/v/s!AjnPcG7NnBQhjLRe7Xn0tbyeodYkIw

 

[Bt Doctur]

You should test the fuel pressure first, you need approx 30 psi. Second you should be be seeing any bubbles .Either the system is sucking air or the fuel filter assembly is sucking in air.

 

[sebbi69]

Thanks Bt Doctor. I assume you mean you “shouldn’t” be seeing bubbles?