Can anyone help on this....

[stanler1@bellsouth.net]

I have a 2003 OX66 225 and lately it has been acting up when running at a constant speed. It will run along at 4000 rpm and then slow down to 3400 for about 5-8 seconds, then throttle back up to 4000 again. It keeps doing this about every 20-30 seconds, and it's getting quite bothersome. Does anyone have any ideas? I have already replaced the fuel/water seperation filter, and cleaned the filter in the vapor seperator tank. Any adivice will be greatly appreciated before I start replacing parts randomly.
Bob

[rodbolt17]

I would check fuel rail pressure and the lift pumps.
rail pressure must be checked at the problem RPM and load or its rather worthless.

[stanler1@bellsouth.net]

Thank you very much for the response. I'll have to get that done and see where it leads. Maybe the fuel pumps?