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1999 mercury 150 EFI saltwater series runs rough at idle

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bryane

Member
Hello all
I have a 150 EFI 1999 model that runs rough at idle, I have checked compression and they are all at 120 psi I have also installed new plugs, Also I was wondering what the mix of oil is because it is on a 19 Silver King and no room for the Oil reservoir, so that is the way it was built, I purchased from the original owner. As you throttle up it runs a very smooth and sounds awesome. I was told when I purchased it a low fuel pressure pump was needed?? I was told by someone else I could count the blinks from the computer it has when key is on if there is a code?? Any Ideas thank you in advance.
 
Have run couple tanks of fuel thru engine and cleaner, same issue exist, low pressure fuel pump replaced. Still the engine runs rough at lower RPM and at idle. Have checked the regulator and it is ok per manual any ideas would be appreciated. Thank you
 
i see you have another thread on this problem and it smooths out at 2k rpm....how does it idle out of gear?
 
Hello
it runs rough out of gear and more noticeable when in gear, it runs like a old Chevy big block with the choke stuck, but does not seem to be loaded up. It runs great the minute you throttle up like instant on. It does not have a fuel smell either. Thank you for responding.
 
Also clean the VST. Replace the top gasket and clean the filter. BE CAREFUL WITH THE FILTER/STRAINER it's NLA (No Longer Available) and if you find one, it's $480.47.
 
Hello all,
Removed injectors and then tested for bleed down and spray, everything was in good working condition, put them back in issue still exist with no difference. I have noticed that the prop is black where it butts up to the foot. Like it is running rich. Have checked the VST for the float being stuck which would cause a rough idle as I have a manual on disc to check different items. Any other help would be appreciated.
Thank you.
 
Hello
I sent them to a fuel injection cleaning company where they checked resistance, pressurized injectors for bleed off and fired injectors checked pulse width at 35 psi wide open pressure 45 psi all injectors tested good and chemical cleaning process performed - no issue
Thank you
 
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