3.0 Stumbles/Bogs

[halleyro]

I have a 2003 3.0L. I just installed a fuel separator kit and the first time out I didn’t notice any issues. But now when in gear the engine stumbles ever so slightly at idle and when I give aggressive throttle it stumbles a lot. If I feather the throttle I can eventually accomplish 4000 RPM but nothing higher than that without constant bogging. The issue doesn’t occur in neutral. Is this issue a result of the addition of the separator kit? I have all new fuel filters at the house and plan on changing them this afternoon. Plugs, Plug wires, Cap and Rotor were replaced this spring. I rebuilt the Carb 2 summers ago and it has run flawlessly. Do I need to adjust the fuel air mixture on the carb after the separator install? Fuel pump bad? Or is this issue merely coincidental and is the result of something else like a bad coil?

Thanks in advance for any and all help!

 

[dubs283]

Is this issue a result of the addition of the separator kit?.... Fuel pump bad?

possibly one or both of these can be an issue. with adding the separator its possible the fuel vacuum has breached the threshold of no more than 2 in/hg. it may be that the fuel pump prior to the addition of the filter could have already been close to the spec of allowable vacuum.

adjusting the fuel/air mixture only pertains to idle

you should check the entire fuel supply system for any restrictions: anti-siphon valve, fuel pick up in the tank, any kinks or hard bends in the fuel lines, etc..

i also recommend a fuel pressure AND vacuum test at all rpms to rule out the fuel pump/fuel supply system

 

[halleyro]

possibly one or both of these can be an issue. with adding the separator its possible the fuel vacuum has breached the threshold of no more than 2 in/hg. it may be that the fuel pump prior to the addition of the filter could have already been close to the spec of allowable vacuum.

adjusting the fuel/air mixture only pertains to idle

you should check the entire fuel supply system for any restrictions: anti-siphon valve, fuel pick up in the tank, any kinks or hard bends in the fuel lines, etc..

i also recommend a fuel pressure AND vacuum test at all rpms to rule out the fuel pump/fuel supply system

Ok I will test the pump for pressure and vacuum. What is the value range I should be in to rule out a bad pump?

 

[dubs283]

Ok I will test the pump for pressure and vacuum. What is the value range I should be in to rule out a bad pump?

low end would be about 4 psi at idle and should see a steady psi throughout the rpm range of 6-7 psi. if the gauge is rapidly bouncing between two limits it can indicate a failing diaphragm.

vacuum should be no more than 2 in/hg, anything higher would indicate a restriction between the fuel pick up and the pump.

is best to observe both readings throughout the rpm range under a load, will require someone else to operate the boat