1999 250 OX 66 possesed motor

[1999 CONTENDER]

This motor has been a pain.Now it runs fine doesnt cut off after fighting that issue for two months. the motor is surging rpms up and down. We were trolling last week and it kept surging like water in fuel. I changed all injectors fuel pressure regulator water seperators decarbed the motor and hooked gas line to a independant tank. It still surges while operating at any set rpms. However it will Idle fine Rodbolt I have read alot of your threads and tryed alot of what u said all but fuel pressure check. i PUT a new high pressure pump on it when it was cutting off. If any body can help pls do. I am just about to give up and try and find me some mercury's. thanks

 

[MnRiverman]

Re: 1999 250 OX 66 possesed motor

Have you cleaned and checked the 02 sensor? Rodbolt may have better ideas.

 

[rodbolt]

Re: 1999 250 OX 66 possesed motor

a fuel rail test is next as well as an O2 sensor output voltage test, test all the spark plug caps for proper resistance as per the service manual. but a fuel rail pressure test is mandatory when testing OX66.
also remember the s250 is a CCS engine which means that between 800 and 2000RPM #2 is shut down and from 650 -2000 RPM #5 is shut down. this motor isnt very smooth at all below 2500 RPM.

 

[1999 CONTENDER]

Re: 1999 250 OX 66 possesed motor

Rod bolt thanks first. I forgot to mention I didnt check the amperage on the O2 sensor but I did change it. I have a spare motor with everything on it Im not fixing it being a parts changer. Im sure you know what I am talking about. Maybe I am just over reacting I havent tested it under load just in tank at home but while trolling it was very noticable. I guess u check the fuel rail pressure off of the schrader valve on the top of the vst tank? I know when it was cutting off it was holding 35 while running and 25-27 while pump not running.I suppose this is correct? I have not done a compression check latley is it possible it has dropped a cylinder. I figured out #5 was not firing while at 1800 rpms because I pulled the Plug wire off and it didnt bite. Thanks