HELP! Yam 250ox66 wont pull over 15 GPH and rpms drop out above 4k, why?

[ShortSale]

Anyone have this problem or know a possible solution? My port side 1999 Yam 250ox66 wont pull more than 15-17gph and when it gets over say 4k RPM's eventually will drop down ...tried changing all low pressure & high pressure fuel pumps and that yellow filter & put on racor filters ...none of those made a difference. Can anyone help?<br /><br />Thanx

 

[rodbolt]

Re: HELP! Yam 250ox66 wont pull over 15 GPH and rpms drop out above 4k, why?

have you tested fuel system vacum> how dirty was the VST filter? you can always plumb in a remote tank to confirm or eliminate the hull fuel system as a source. when was the last O 2 sensor service ?<br />also what is the high pressure fuel gauge reading when the RPM starts falling? if your going to work on it ya have to buy a manual and basic tools and teach yourself the basics of EFI. EFI is incredably simple but no one bothers to try to understand how it works. also test the plug caps and the TPS voltages. all the subsystems have to feed the correct info to the ECM or the ECM is confused. its not real bright. the yamaha diagnostic lamp is inexpensive and will quickly confirm or eliminate the sensors.<br />is the ign timing correct at WOT? has the CPS been tested ?<br /> all of it has to work or none of it does.low fuel flow will fall into two catagories. 1 is it cant get the fuel to the injectors and 2 is the injector on time is not correct due to the ECM's commands. or lack of commands.<br /> post more info on how and when this problem started as well as normal maint done and corrective maint done.

 

[ShortSale]

Re: HELP! Yam 250ox66 wont pull over 15 GPH and rpms drop out above 4k, why?

Thanx rodbolt for replying to my problem, well I bought the boat used in 2002 so it was 3 years old so I can't tell u what maintenance was done before I bought it but I can tell that as far as I can remember at least 2 years now the same motor held for a minute or 2 at WOT would go into slow mode or what felt like it was slow mode (rpms drop down to day idle)....if i backed off throttle then powered back up it would be fine.....I never cruised at WOT throttle or higher than 44 rpms so it didnt bother me that it did this...just at end of last season the motor started dropping rpm now at say anythign held over 4k for 5 or ten mins...that is when I had a mechaninc start to work on it..... All maint. I have done since i owned the boat was change plugs each year, change lower fluid, change water pumps. Nothing else...since this problem at end of last year I have changed 3 low pressure fuel pumps & the mechanic thgt it mite be high pressure pump so he changed that but thats not it so he gonna try some other stuff (next he will bring down a 5 gallon tank and hook up directly to rule out hull fuel system) and put my old pump back in...he did put a fuel pressure guage on it and said when rpms fell off it was loosing pressure... What else should I reccomend he try?

 

[ShortSale]

Re: HELP! Yam 250ox66 wont pull over 15 GPH and rpms drop out above 4k, why?

Sorry rodbolt, I forgot to mention the mechaninc did say the O2 sensor bolts looked like someone had worked on them... and he did look at it & said it looked ok

 

[rodbolt]

Re: HELP! Yam 250ox66 wont pull over 15 GPH and rpms drop out above 4k, why?

so your telling me you knew it had a problem but what the hay rune er anyway. not wise nor money saving. has a compression test been run? if not run one. your maint schedule is not correct. if you dont maintain that OX66 you will replace them. they will pop pistons. I rarly uses a remote tank, it just adds time. a fuel system vacum check will tell me what, where and if there is a restriction. sounds like the tech is plugging parts at it as well as half arseing the maint. I see it weekly, yea I knew it was FUBAR but we ran it anyway and now its locked up. I do know where a pair of low hour 250 1999 models are that are for sale though. the low pressure pumps are a maint item. replace them every three years or 300 hours whichever comes first. the VST maint is annually OR 200 hours. the O2 sensor is annually OR 200 hours whichever comes firts. as is the maint on the remote oil tank and the engine tank sensors. the engine tank water trap is a 6 months OR 100 hours whichever comes first. either keep on top of the maint or do nothing and replace the motors periodically.

 

[ShortSale]

Re: HELP! Yam 250ox66 wont pull over 15 GPH and rpms drop out above 4k, why?

wow....thats a wake up call! ok i need a maintenance schedule and will do all required maint on both motors they ran so good till now did not know needed other things done besides plugs every year and lower gear oil.... so ur saying next thing i should do is a compression check?

 

[rodbolt]

Re: HELP! Yam 250ox66 wont pull over 15 GPH and rpms drop out above 4k, why?

on the affected motor. running lean can cause piston failure. the stupid ecm cant tell if the O2 sensor is feeding good or bad info. it just monitors if the circuit is complete. the first sign of an O2 sensor problem is a lean out above 4K. the second is usually #1 piston failure. look in the 05 marine tech guide for the maint schedule on OX66 EFI. note that its a calander or hourly whichever occurs first. and pray your tech has a clue whats going on and why. the reason I rarly use a remote tank is if it runs ok with a remote I still have to use the vacum gauge to find the restriction. so I start with the vacum gauge and it will tell me right off if the fuel supply side is ok or not. saves time and a water test. if its not ok at the pump suction side, pump side of the fuel line check valve, ya have to move the gauge back until fuel system vacum is below 6" Hg on a 250. should be between 1.5" Hg and about 5'Hg under ideal conditions. anything at 6" or above is a problem. can lead to fuel boiling in the lines and a lack of fuel at the vapor seperator. no fuel, no pressure on the rail and a lean condition in the cylinder.

 

[ShortSale]

Re: HELP! Yam 250ox66 wont pull over 15 GPH and rpms drop out above 4k, why?

ok will tell the tech to try those vacum tests, unles sits somethign i can do myself?...where do i look at or get the '05 marine tech guide...i do have a shop manual for the motor that should have same maint schedule or no?...how can u tell if the 02 sensor is bad? But in the likely case ur telling me that the #1 piston is on its way out?

 

[rodbolt]

Re: HELP! Yam 250ox66 wont pull over 15 GPH and rpms drop out above 4k, why?

pistons in a two stroke dont gradually fail. it works or its blown. never said a piston was going just said it can be the second symptom of a bad O2 sensor. the best way to test the sensor is with the two wire test harness and a DVM. with the gearcase submerged to normal depth and the airbox removed cover the #1 cyl air bypass hole and watch the meter. then uncover it and watch the meter. all tests should be done after at least a 5 min warm up period. the tech guide is avalible from a dealer it usually has the laatest service reccomendations.

 

[ShortSale]

Re: HELP! Yam 250ox66 wont pull over 15 GPH and rpms drop out above 4k, why?

You gonna be on Long Island anytime soon ???????

 

[tsmullins]

Re: HELP! Yam 250ox66 wont pull over 15 GPH and rpms drop out above 4k, why?

Hey ShortSale? Did you resolve this issue? If so what was the cause?<br /><br />Shane

 

[ShortSale]

Re: HELP! Yam 250ox66 wont pull over 15 GPH and rpms drop out above 4k, why?

Not yet...will be working this week hopefully...trying to gather as much research as possible before I have my tech look at it! I will post what we tried and the results.

 

[ShortSale]

Re: HELP! Yam 250ox66 wont pull over 15 GPH and rpms drop out above 4k, why?

Found the problem ....collapsed/kinked fuel line in the rigging tube right before it enters the motor. My tech kept bypassing sections of the fuel line and once that was bypassed she ran perfect!...Before that he put pressure guage to make sure it was fuel problem... fuel pressure began to drop out above 4k rpms then she was leaning out and dieing....i had to leave but he ran new fuel line and should be all set now...thanx RODBOLT for ur input i feel i now have better grip on how to troubleshoot!

 

[rodbolt]

Re: HELP! Yam 250ox66 wont pull over 15 GPH and rpms drop out above 4k, why?

glad ya found it. now you have a better understanding of how it all works.