I've got a box full of parts... Where do I start! (OX66 250)

[SBH2OMan]

Just bought a boat with an older Ox66 and unknown service record. She seems to run nicely except for at WOT she exhibits the infamous "fall back" symptom where she'll run up to 5,100 or so then drop back to the low 4's (pegging the GPH gauge) until I back slightly off the throttle, then she'll run back up to the low 5's. If not run at WOT, you'd never know there was a problem. On a Parker 2320 EC, she's burning about 12 gph at 22 knots, and I think there may be a bit of upside to that fuel burn rate.

I want to go through all the regular maintenance parts to establish a good "baseline" but of course I can't do everything in one day. So the question is - "Where to start?"

I've got a wonderful box of new parts sitting here ($600 worth) and wondering if I'm on the right track. My plan is as follows:

Phase I: fuel system

• Replace Sierra 21 micron filter with Racor 10 micron unit with clear bowl
• Replace engine mounted fuel filter & gasket
• Replace (3) low pressure fuel pumps
• Replace VST filter (damn those things are expensive for what they are!)

Phase II: Cooling System

• Replace thermostats (2)
• Complete rebuild of water pump (including ALL new parts)
• Replace pressure relief valve ("poppet" valve)

Phase III: General tune-up

• Clean O2 sensor and dip tube
• New Spark Plugs
• ???
• (Already replaced LU oil during pre-purchase inspection)

So how are my priorities? Any advice, or is there anything I might be missing? What else goes into a "tune-up"? I have the factory manual on my computer, but have not read all the relevant sections yet...

Thanks in advance!

 

[rodbolt]

Re: I've got a box full of parts... Where do I start! (OX66 250)

to start with there is no "infamous" fall back, simply a standard lack of maint.\
there is no phase 1 2 or 3, there is simply standard routine maint.
your also going to need a service manual or at least the tuneup spec guide,a digital multi meter and a fuel rail pressure tester and a compression guage.
post a full model number as the ox66 is simply the designator that its two stroke EFI.
doesnt say whether its 3.1L,2.6L or if it does or does not use CCS.
post the full model number.

 

[SBH2OMan]

Re: I've got a box full of parts... Where do I start! (OX66 250)

to start with there is no "infamous" fall back, simply a standard lack of maint.\
there is no phase 1 2 or 3, there is simply standard routine maint.
your also going to need a service manual or at least the tuneup spec guide,a digital multi meter and a fuel rail pressure tester and a compression guage.
post a full model number as the ox66 is simply the designator that its two stroke EFI.
doesnt say whether its 3.1L,2.6L or if it does or does not use CCS.
post the full model number.

First of all, Rodbolt, thanks for taking the time to jump in and respond to my query. I've spent quite a lot of time wrenching on automotive engines and transmissions (rebuilt a few from scratch including all the machining work), but this is my first foray into marine engines, so please be patient with some of my "noobness".

Let me respond to some of your questions/comments:

Pardon my "infamous" reference, but it seems that lack of proper maintenance on this motor often results in a commonly reported problem with WOT performance such as I described. My research indicates that this can be caused by a variety of problems, and my goal is to create a "baseline" of replaced components before I begin formal diagnosis. Perhaps a foolish waste of money, but isn't that already what most people say about boats in general?

I used the term "phases" because I cannot physically complete all the work in a single session. That's really what I meant, but its really not all that important, I suppose...

I do have a factory service manual, digital multimeter, and compression gauge. (I have already checked the compression, and while it seemed "low" overall (high 90's low 100s), all cylinders were within <6% of each other). The powerhead was rebuilt in 2005 (about 150 hours ago), and I have been told that rebuilt marine engines are always a bit "loose" compared to new motors because they cannot be align-bored.

The model number is S250TXRX

Once I replace all these parts, I plan to continue with a meticulous step-by-step diagnosis, following the procedures outlined in the service manual. If I should be so lucky as to solve the problem by replacing these parts, I will consider myself fortunate and then have my "baseline" for a regular and thorough maintenance schedule (I maintain a computerized log of all maintenance performed).

Thanks again!

-Brent

 

[rodbolt]

Re: I've got a box full of parts... Where do I start! (OX66 250)

whoever tole ya da sheet about align boring a two stroke? NEVER go back.
they are a christmas turkey.
align boring IS NOT a two strokew deal.
all in the 4stoke world with cranks that use main caps, that align boring means is the main bearing bores are in alignment.
nothing to do with piston bores.
your phase thing.
suxs
its to simple to just do it all at once.
will take about 4 hours but its not hard.
S250TXRX
OX66 EFI, trim,25" transom,remote control and its a 1999 production run.
this is NOT an automotive engine, treat it as such and it blows a piston.
compression is low? tell me where you got compression spec numbers.
then ill chat about them.
but the loose thing tells me your tech is a christmas turkey.
cant get over that.
he aint got a clue and you aint either.
thats why some of us are here.
you can diagnose and repiar this engine or you can chunk a lot of expensive parts at it.
dude, its an incredibly simple speed density EFI set up.
it will most times trouble shoot itself if ya listen.
NO such thing as a tight OR loose engine.
its either repaired to factory specs or it got patched.
dont care if its grannys grocery getter, an outboard or an airplane engine.
they all suck, squeeze, bang and blow.

 

[SBH2OMan]

Re: I've got a box full of parts... Where do I start! (OX66 250)

whoever tole ya da sheet about align boring a two stroke? NEVER go back.
they are a christmas turkey.

Umm.. it was a guy on an Internet forum (not this one) :redface:

your phase thing.
suxs
its to simple to just do it all at once.
will take about 4 hours but its not hard.

Well, since it was my first time through today, it took me about 4 hours to very carefully and deliberately:
Replace the external fuel filter with a Racor unit with clear bowl
Replace the three LP fuel pumps (two failed the leak test in the manual), Replace the VST filter (the one in there was brown and shorter than the blue replacement - I assume it means that was close to an original "old style" filter)
Replace internal fuel filter and o-rings, and inspect all the fuel lines for cracks and wear.

Then it got dark.

compression is low? tell me where you got compression spec numbers.
then ill chat about them.
but the loose thing tells me your tech is a christmas turkey.
cant get over that.
he aint got a clue and you aint either.

The compression spec numbers were given to me by a certified Yamaha mechanic (that might mean diddly, I dunno), and provided to me as part of the pre-purchase mechanical inspection (that cost me $350 by the way!)
Here is a direct quote from his report:
"1)105psi, 2)96psi, 3)104psi, 4)93psi, 5)98psi, 6)94psi. check spark ? good."

dude, its an incredibly simple speed density EFI set up.
it will most times trouble shoot itself if ya listen.

Yes, after working on it today, I can see it is much simpler than I originally thought.

..they all suck, squeeze, bang and blow.

There is just so much potential for a response to that quip, but I'm restraining myself.


Thanks again. BTW, I could not find any torque specs for the screws (some might call them "bolts") that hold down the LP fuel pumps. I snugged them to where I thought they were when I pulled them apart. I'm assuming it needed to be tight enough to "crush" the fiber gaskets (which I replaced). I also used genuine OEM black zip ties to re-secure the fuel lines.

 

[rodbolt]

Re: I've got a box full of parts... Where do I start! (OX66 250)

somewhere in the service manual is a general torque spec for 6mm bolts.
there is no other call out for the fuel pump mounting.
somthing is wrong with the vst filter.
post the part number you installed and ill double check it.
typicaly the 3.1,especially units produced after 2003, run about 85 PSI on a compression test but Yamaha does NOT post any specifications for compression.
do a forum search on O2 sensor voltage test. must be tested as it can blow a piston.
unlike a car that will simply go to open loop and set the check engine lamp this ECU will react to a faulty signal and can lean it out above 4000 RPM and smoke a piston.
if the power head has been replaced with a unit manufactured after mid 2003 the O2 sensor gasket set in the parts book will be the wrong one, use the wrong mounting kit and POOF go da pistons.
gotta watch most dealership and internet stuff.
however some of us actually have some training and actualy do this for a living and have for over 30 years.
go by the dealersip,check the tech bullitens for O2 sensor output tests, pay NO attention to the flame test as its useless.
also look for the tech bulliten about the thermostat covers, it applicable to about your year model.
when you do the water pump do a forum search for v4 water pump replacement.
only difference between that post and yours is you have one more bolt securing the lowerunit to the midsection.
when you remove, clean the grommet pocket, and install a new pressure control valve grommet. its easy to drop the new grommet into the cover.
if you do stop,post, ill explain how to fish it out.

 

[SBH2OMan]

Re: I've got a box full of parts... Where do I start! (OX66 250)

somewhere in the service manual is a general torque spec for 6mm bolts.
there is no other call out for the fuel pump mounting.


somthing is wrong with the vst filter.
post the part number you installed and ill double check it.

Here's what the one I took out looked like:

Here's the one I replaced it with:
Product Code 65L-13915-00-00
http://www.simyamaha.com/Yamaha_Fuel_Pump_Filter_p/65l-13915-00-00.htm

When I pulled the old one out, I looked online and saw several references to "old style" VST filters that had been replaced with a "new style". The source for the part was reputable and apparently knowledgeable, but maybe there is an issue with the newer powerhead...? Are these different filters not interchangeable?

typicaly the 3.1,especially units produced after 2003, run about 85 PSI on a compression test but Yamaha does NOT post any specifications for compression.

Good to hear! Sounds like I'm in the "normal" range then.

do a forum search on O2 sensor voltage test. must be tested as it can blow a piston.
unlike a car that will simply go to open loop and set the check engine lamp this ECU will react to a faulty signal and can lean it out above 4000 RPM and smoke a piston.

I don't have a bucket big enough to run the motor, so I have to wait until I'm on the water to test the O2 sensor, which I plan to do tomorrow dockside along with adjusting the idle (it was idling at about 1,100 rpm before I replaced the fuel components)

if the power head has been replaced with a unit manufactured after mid 2003 the O2 sensor gasket set in the parts book will be the wrong one, use the wrong mounting kit and POOF go da pistons.

How can I positively ID the year of the powerhead? Obviously the model & SN are stamped on the outside case, so it doesn't tell me what the actual year of the powerhead itself might be... Are there physical clues I can look for if there is no stamp or tag that is typically affixed?

gotta watch most dealership and internet stuff.
however some of us actually have some training and actualy do this for a living and have for over 30 years.
go by the dealersip,check the tech bullitens for O2 sensor output tests, pay NO attention to the flame test as its useless.

also look for the tech bulliten about the thermostat covers, it applicable to about your year model.

when you do the water pump do a forum search for v4 water pump replacement.
only difference between that post and yours is you have one more bolt securing the lowerunit to the midsection.
when you remove, clean the grommet pocket, and install a new pressure control valve grommet. its easy to drop the new grommet into the cover.
if you do stop,post, ill explain how to fish it out.

Thanks for the additional tips!

 

[SBH2OMan]

Re: I've got a box full of parts... Where do I start! (OX66 250)

OK, I just went poking through the parts books for later model 250's and it looks like from 2000 onward, the VST filter looks like the one I removed. This would explain why the O-ring didn't look like it would fit correctly for the float chamber (I re-used the old one).

So the important question is whether these VST filters are interchangeable....???

My guess is that it is safer to clean and re-install the old one then figure out what year the actual powerhead is and order the correct parts for it.

The other parts (LP fuel pump & internal fuel filter) appears to be direct replacements for the originals, so they looked the same.

-Brent

 

[rodbolt]

Re: I've got a box full of parts... Where do I start! (OX66 250)

only way to tell if the powerhead is mid 03 and up is by removing the O2 sensor holder,mid 03 and down the block surface is flat,mid 03 and up the draw tube area is protruded out about3/8ths of an inch.
the mounting hardware is different and the correct stuff MUST be used.
I am at work now looking at the parts diagram for the s250txrx, calls for filter 66k-13915.
however its possible someone changed the complete VST.
the 65l was only used on the 97-98 ox66 3.1L engines.
NO such thing as old or new style VST filters.
its either the correct part for the VST ot its simply the wrong part,wont fit and will cause problems.
the only way to positively ID the VST is look at the screws that hold the tank top to the body.
the body that uses the 65L filter has 3 larger diameter screws than the rest of the cover screws.
the body that uses the 66K filter all the cover to body screws are the same size.
if you use the 65L in the 66K tank it gets mushed.
if you use the 66K filter in the 65L tank it doesnt touch and the pump will fall off the cover.
gotta watch sources.
look at the 3 screws at the front of the tank and compare them with the ones at the back.
if they are all the same size you need a 66K filter.

 

[rodbolt]

Re: I've got a box full of parts... Where do I start! (OX66 250)

on the idle speed, ITS NOT ADJUSTABLE.
same as an MPI automobile, it works as designed or its broke.
1100 RPM idle is what you get if any sensor,other than O2, fails or is out of range.
depending on the failure top speed may or may not be reached.
say like unplug the knock sensor, timing defaults to fixed 7* BTDC idle speed is about 1100 fuel is fixed top speed cannot be reached.
take a coolent or intake air temp failure, timing will be fixed 7* BTDC at low speed,idle increases to about 1100, top speed can be reached.
see how simple this all is?
dang motor will test itself if you let it.

 

[SBH2OMan]

Re: I've got a box full of parts... Where do I start! (OX66 250)

on the idle speed, ITS NOT ADJUSTABLE.
same as an MPI automobile, it works as designed or its broke.

Hmm... Then I am puzzled by section 3-6 in the manual:

 

[SBH2OMan]

Re: I've got a box full of parts... Where do I start! (OX66 250)

only way to tell if the powerhead is mid 03 and up is by removing the O2 sensor holder,mid 03 and down the block surface is flat,mid 03 and up the draw tube area is protruded out about3/8ths of an inch.
the mounting hardware is different and the correct stuff MUST be used.
I am at work now looking at the parts diagram for the s250txrx, calls for filter 66k-13915.
however its possible someone changed the complete VST.
the 65l was only used on the 97-98 ox66 3.1L engines.
NO such thing as old or new style VST filters.
its either the correct part for the VST ot its simply the wrong part,wont fit and will cause problems.
the only way to positively ID the VST is look at the screws that hold the tank top to the body.
the body that uses the 65L filter has 3 larger diameter screws than the rest of the cover screws.
the body that uses the 66K filter all the cover to body screws are the same size.
if you use the 65L in the 66K tank it gets mushed.
if you use the 66K filter in the 65L tank it doesnt touch and the pump will fall off the cover.
gotta watch sources.
look at the 3 screws at the front of the tank and compare them with the ones at the back.
if they are all the same size you need a 66K filter.

Then I definitely have the 66K filter type body, as all the screws were the same (I checked them as I pulled them from the unit). When I assembled it, everything seemed to go together well. (I used to wrench on my old BMW motorcycles a lot and one thing I learned was that if something didn't fit together EXACTLY and SMOOTHLY, I was doing something wrong. Ever since then, I've developed a sensitivity for how things fit together..

I'll definitely be pulling the 65L filter back out and replacing with the old 66K and getting a replacement. Is carb intake cleaner OK to use for cleaning it, or should I just use some Simple Green and water? (or gasoline?)

It sounds like SIM Yamaha is selling the wrong VST filter for the S250TXRX, since they shipped me (and specified) the 65L filter (you can look it up on their web site and see for yourself). This is good news for two reasons:
1. The filter in my motor to start with was the correct on for a S250TXRX and 2. I can expect them to refund my money for the filter and gasket since they shipped the wrong ones! (Over $100 for the pair!)

Thanks again!!!

 

[rodbolt]

Re: I've got a box full of parts... Where do I start! (OX66 250)

your simply missing the picture./
that and a few procedures.
first is to test the TPS reference voltage,second is to test TPS output, then adjust idle.
however once a stable correct idle speed is obtained it will remain that way forever or until something BREAKS.
same as your car.
once the EFI system is set up its will never change until something breaks.
then an idle screw adjustment WONT help. may mask issues but its not the issue.
over the years I have twisted wrenches for Ford,Chevrolet, a few independants and for Volvo-penta,Mercruiser,suzuki,Honda,Force'mercury/mariner, Tohatsu,and go-devil.
I am currently a Yamaha Master technician.
google yamaha master tech and I am the one in wanchese NC.
along the way I spent 6 years programming and setting up CNC lathes and mills.
I also spent almost 6 years in the USN as an FC.
thats part of the US navy's advanced electronics field.
I actually have a random idea of an s250txrx.

 

[SBH2OMan]

Re: I've got a box full of parts... Where do I start! (OX66 250)

Thanks again Rodbolt. Your experience clearly shows, and I appreciate the help and wisdom.

Looking up the parts diagram for the 1999 S250TXRX online, I find this schematic:
http://www.boats.net/parts/search/Yamaha/Outboard/1999/S250TXRX/FUEL INJECTION PUMP/parts.html

Which indicates that for the S250TXRX the 65L is the correct filter. This seems to contradict the manuals you are using for reference. What could cause this?

HOWEVER, looking at the schematic at this location for the S250TXRX:
http://parts.yamaha-motor.com/?ls=outboard

coincides with the information you are using.

Now I'm TOTALLY confused....

I'm wondering if either:

A) The same model used different fuel injection tank/pump assemblies (65L and 66K) or there was a mid-year change OR

B) The parts are interchangeable (I doubt it) OR

C) One of these schematics is wrong OR

D) Someone bolted a different injection pump assembly to my motor

Safest course of action is to treat the assembly as a 66K and be careful about the other model year variations when ordering parts...

 

[rodbolt]

Re: I've got a box full of parts... Where do I start! (OX66 250)

like I said
I am sitting here at work on thanksgiving day cause one of my commercial guys showed up broke last night about 4PM.
he is done and gone now I am killing yet more time, that or hiding from the missus.
I am looking at both yamaha parts smart and yamaha parts manager pro software parts catalogs.
but I can also tell you from experience that if all the VST screws are the same size it takes the 66k.
if 3 are larger than the rest at the fwd end of the tank it takes the 65L.
the 65L will also work on some of the mercury 3.0L EFI outboards .
if someone swapped the COMPLETE vst from the 97-98 s250 then it would have the screw differences and use the 65L.
but as your 65L tank gasket doesnt fit I would imagine you need gasket 66K-14984 instead of 65L-14984. notice a pattern here with the 66K and the 65L prefix?

 

[SBH2OMan]

Re: I've got a box full of parts... Where do I start! (OX66 250)

on the idle speed, ITS NOT ADJUSTABLE.
same as an MPI automobile, it works as designed or its broke.
1100 RPM idle is what you get if any sensor,other than O2, fails or is out of range.
depending on the failure top speed may or may not be reached.
say like unplug the knock sensor, timing defaults to fixed 7* BTDC idle speed is about 1100 fuel is fixed top speed cannot be reached.
take a coolent or intake air temp failure, timing will be fixed 7* BTDC at low speed,idle increases to about 1100, top speed can be reached.
see how simple this all is?
dang motor will test itself if you let it.

By the way, I see no reference sections for testing the various sensors. (I have to say that this Yamaha service manual is a big disappointment compared to my collection of Bentley manuals for automotive applications...)

Is there a thread on this forum for the procedures to test the various sensors?

Thanks,

Brent

 

[SBH2OMan]

Re: I've got a box full of parts... Where do I start! (OX66 250)

...but as your 65L tank gasket doesnt fit I would imagine you need gasket 66K-14984 instead of 65L-14984. notice a pattern here with the 66K and the 65L prefix?

Yup, got it figured out. It is obvious that I have the 66K variation and need new parts. What is interesting is the incorrect parts schematics that many web sites are showing!

Hopefully SIM will refund my money even though the parts were opened and installed briefly, and exchange them for the correct ones.

 

[rodbolt]

Re: I've got a box full of parts... Where do I start! (OX66 250)

section 8, electrical.
has every sensor spec you need and how to check them.

 

[SBH2OMan]

Re: I've got a box full of parts... Where do I start! (OX66 250)

section 8, electrical.
has every sensor spec you need and how to check them.

Oops - duh. I'm looking at it on my computer and skipped past that part looking for a "reference" section. Thanks.

So if I understand your comments, to address high idle speed:

1. Test TPS
2. Test Coolant sensor
3. Test Knock sensor
4. If all OK, then use procedure outlined in section 3-6...?

 

[rodbolt]

Re: I've got a box full of parts... Where do I start! (OX66 250)

best procedure, especially if your going to do your own maint.
is to purchase the diagnostic test lamp.
its about 80 bucks and will flash codes.
no codes no faults.
the exception is the O2 sensor which has NO codes associated with it.
when cold,below about 113*F, that motor will idle about 1100-1200 RPM.
code 33 will be flashing.
once warm the RPM will drop to the designated idle speed and code 1 will be displayed if everything is happy.
if the CTS fails or becomes unplugged the system will set code 13 unless its an in range failure.
lets say the CTS is ALWAYS telling the ECU that the engine is at 90*F.
guess what that dumbass ECU is gonna do.
its gonna fix fuel rich at low speed,fix idle timing at 7* BTDC.
idle speed will remain about 1100 RPM and top speed CAN be reached.
unplug the Knock sensor or the TPS.
stupid ECU is gonna lock ign timing at 7* BTDC,fix fuel rich and idle speed will be about 1100 and top speed CANNOT be reached.
drop 300 bucks on some equipment.
diagnostic test lamp, also known as the winky blinky 80-90 buxs.
decent digital multi meter from radio shack, 30 bucks.
DVA adapter another 50-60 bucks.
fuel rail test guage, 50 bucks.
compression tester,20 bucks.
spark tester can be made for maybe 10 bucks
with the above equipment the ENTIRE engine can be diagnosed within an hour.
then there is no guessing,hemming,hawing,gnashing of teeth nor wailing.