350 mag 5.7l skipping

[Riverview3]

Totally lost, please help. 2007 Chaparral 236si with 350 mag 5.7l and bravo III. Boat cranks and idles great. When given gas to accelerate motor starts skipping and keeps skipping as long as you accelerate. When slow down back to idle it runs great. We have replaced rotor and distributor and the small Infiniti on piece up under it. New spark plugs. New spark plug wires. New rectifier. Any ideas???? Still skips when you accelerate. Seems like we are missing something because it runs so great until you accelerate.

 

[Scott Danforth]

Most likely fuel system related

 

[Riverview3]

Most likely fuel system related

We replaced both of the filters and thought we had tested the fuel pump. What part of the fuel system are you thinking?

 

[Scott Danforth]

Start with your fuel pressure, at idle, and under load

Did you inspect the contents of the fuel filters?

 

[Riverview3]

Start with your fuel pressure, at idle, and under load

Did you inspect the contents of the fuel filters?

Yes the round filter was basically ok. And the little filter had very little sludge but not bad. And to our knowledge has never been changed. We tried to check pressure on fuel filter but it doesn’t have a screw in connector to attach a pressure reader. It is an oring and push in and snap connector.

 

[dubs283]

It is an oring and push in and snap connector.

is the engine efi/mpi or carbureted?

 

[Riverview3]

It is mpi. And it is an oring and push

 

[alldodge]

Serial number?

 

[dubs283]

It is mpi. And it is an oring and push

the only fuel pressure tester port i've seen on a merc mpi is a shrader valve style on the fuel rail

can't say ive ever seen a fuel pressure tester port on or near a fuel filter, the closest would be an in-line adapter used on a carburetor that threads into the filter housing at the carb inlet

 

[Riverview3]

Ok. We can do that. What should the pressure in the rail be when running?

 

[dubs283]

mercury has a few different specs for fuel pressure but generally they are around 40 psi for mpi engines

be sure to take pressure readings throughout the rpm range and under a load, pressure should remain constant and not exhibit any major swings in readings

 

[Riverview3]

Thank you so much! Will try tomorrow!

 

[QBhoy]

Sounds like water in the fuel. What plugs did you put in it ? Got to be iridium in these.