2002 150 VMAX OX66 high RPM surge

[giffman]

Engine starts and runs perfect from idle to about 4500 rpm. At sustained high rpm's engine will surge approx 100-200 rpms in intervals of 10-20 seconds. Boat should run 47mph top speed but will not get over 42mph currently.

O2 sensor cleaned and plugs replaced approx 25 hrs ago. Shop said VST filter was removed and cleaned at the same time. (I thought they had to be replaced...?) I checked the plugs, they look fine.

I'll start with the simple stuff this weekend - replacing the fuel/water separator, check the primer bulb but from what I've read it sounds like this may be high pressure fuel pump? Fuel pump diaphragm?

 

[rodbolt]

Re: 2002 150 VMAX OX66 high RPM surge

test the voltage output from the O2 sensor at 3000 to 4000 RPM it should be .3 plus or minus about .1V. atthe ame time test the fuel system vacum at the inlet to the lower fuel pump, it must be less than 4" hg. at the same time you can test the high pressure fuel, it must remain steady at 35 PSI plus or minus about 2 PSI. any more variation will play havoc. at the same time you can test TPS voltage if you wish but your describing a fuel problem.
as far as speed its irrelavent, to mny external conditions affect the motor. it should be capeable of turning 5600 at least.
a quick run on a test wheel or dyno will isolate any hull/set up isues from actual engine isue.
I wish they would make fuel water seperators and tachometers mandatory and speedometers illegal.

 

[giffman]

Re: 2002 150 VMAX OX66 high RPM surge

ya, i know its more a function of engine rpm's in this case. I'll pay more attention next time out but if memory serves me 5000-5200 is fast as it will turn now. B4 it would run 5600.

thanks rodbolt !