250 ox66 Rough/Low RPMS

[jlopvar]

2000 250 EFIs. One motor was running rough/stalling and smoking so I recently did the following to both engines as preventative maintenance:

1) Decarboned with seafoam
2) Change low pressure pumps
3) Clean o2 sensor
4) New Thermostats
5) New plugs
6) Cleaned vst filters

Now engines will not run above about 3500 rpms and surge somewhat. Sound rough and seem sluggish, vibrating. While returning to dock at 3k temp alarm on one engine sounded. Limped badck on remaining engine.

Any thoughts about these symptoms? Thanks.

 

[bgbass.1]

Re: 250 ox66 Rough/Low RPMS

sounds like you have a overheat. could have cooked the haed gasket.

 

[rodbolt]

Re: 250 ox66 Rough/Low RPMS

no, your doing corrective maint, preventative and you would not be posting.
cleaned O2 sensors? did ya test the O2 sensor voltage output when done? have ya placed the diagnostic test lamp on it and looked for codes? have ya tested the spark plug caps? lots and lots of stuff to do. yet its all in the maint guide under yearly OR the hourly maint.
when was the last complete cooling system tune up?
there is a tech bulliten out on the 3.1L tstat housings but I cant remember if its applicable to your engine.

 

[jlopvar]

Re: 250 ox66 Rough/Low RPMS

Last service was in May. I need to test voltage on o2 and am looking for diagnostic lamp...will update, thanks.

 

[rodbolt]

Re: 250 ox66 Rough/Low RPMS

not neaning to be sharp but there is a lot going on all at the same time on that engine.
it all works together or it doesnt work well at all. bad thing is,like modern cars, a certain amount of test eqipment is MANDATORY to do any maint.
without it there isnt much the average backyard guy can do, ya either buy the stuff or poke-N-hope.
both can get expensive.