5.0 Mercruiser MPI not running right HELP PLEASE!!!

[weshod]

I have a 5.0 Mercruiser MPI in a 2006 crown line with 200 hou s. Roughly half the time it has no power coming out of the hole. It will surge at fast idle and running 3000-3500rpm will drop 3-400 rpm then pick back up. Today wouldn't run over 4000rpm. It has been to the shop twice, had spark plugs, wires, distributor cap replaced. Fuel filter has been changed several times. I ran it completely out of fuel Friday, then changed filter and still running the same. The shop I have taken it to is supposed to be reputable. When I told the service manager that it still ran the same after two trips she just shrugged her shoulders. I will be going to a different shop now but Any ideas would be greatly appreciated.

 

[Bt Doctur]

measure the rail pressure , could have a fuel pump going bad. without 42 psi your not going nowhere

 

[weshod]

Thanks for the response. I should add that it seems to get worse as the engine warms up.

 

[Scott Danforth]

check the contents of the fuel filter to make sure is only fuel and not fuel and water.

measure fuel pressure.

 

[cableguy1979]

I had this same thing happen to me once. It turned out to be the backflow preventer on the fuel tank. it had gotten a small piece of Teflon tape stuck in the ball. Engine surged and eventually got to where the engine would shut off but would start back up and run. just a thought but its worth looking at it. You can rent a fuel pressure gauge at AutoZone and check it.