225 ox66 problems...

Long story short I put a used 1998 225 ox66 on my boat last spring. The engine has not run right since day one. After doing some research and buying the maintenance guide I started cleaning and testing parts. Now the engine runs good from 900-4500 rpm. After I did all the basic maintenance and replaced some parts I still had two consistent problems.

1) After about 5 - 10 seconds the engine loses exactly 500 rpm at WOT . If it goes up to 5400 it will drop to 4900. If it gets to 5500 it will go to 5000. I asked a yamaha tech about this and they said that rpm loss is the equivalent to losing one cylinder. What could cause one cylinder to drop out at WOT?

2) If I restart the engine when it is at operating temp it will smoke like crazy. When I start the engine cold it does not smoke. After reading some threads about these engines smoking I will have to take a look at the check valve and seals on the oil pump. Could this be something else?

Thanks for the help in advance...

Buddy

Re: 225 ox66 problems...

glad you got a manual. there is a lot of great info on this site. helped me address my 1997 225 efi issues which were mainly fuel related issues.

please provide specifics on the basic maintenance and what parts were changed?

to answer questions:
1) this sounds like a vst pressure drop. is it maintaining 35 psi?
2) does pumping the primer ball before you warm start reduce the smoking?

have you addressed:
checked low pressure pumps
clean vst filter
clean pressure regulator screen
clean fuel injector screens
test O2 sensor. Clean
are spark plug caps in spec,
water pump change
thermostats.
link and synch
oil rod adjustment.

Re: 225 ox66 problems...

Thanks for the fast reply. One of the first things I did was test the fuel pressure at wot. I did have a drop in fuel pressure which I thought was the problem. As soon as the pressure dropped I would lose 500rpm. I tried everything to fix this problem. When I say everything I mean everything. The shop that did the install replaced all the low pressure fuel pumps. So I thought the problem had to be the high pressure fuel pump. That was an expensive mistake. After testing everything 3 more times I installed an electric fuel pump to bypass the low pressure pumps to completely rule them out. It still had the same problem. It ended up being the resistor for the high pressure pump. Now it holds 35psi and the rpms still drop.

I have not tried pumping the ball after it was warmed up. If this does make it smoke less what would you say the problem is?

The maintenance I have done is:

Adjusted oil pump rod - it was never adjusted after the initial break-in

Tested the spark plug caps - replaced 2 that were not in spec and the engines is much smoother at idle in gear. It still shakes a little so I might just replace the rest.

Cleaned the o2 sensor a few times - after decarbing I took it out and cleaned it again. That thing gets dirty really fast. I also tested the o2 sensor but I did the flame test. I read on here that this test is worthless?

Replaced the thermostats

Cleaned the VST tank a few times and the new pump came with a filter

Cleaned the screens on the injectors

Tested the fuel pressure regulator


I also got a winky blinky and the engine throws no codes. I probably should get the tps test harness and o2 sensor test harness next.


Buddy

Re: 225 ox66 problems...

clean the pressure regulator screen.
check that there is no trash in the vst sloshing around.
verify tps.
check the o2 sensor using the tech bulletin. make sure it is between 0.3 and 0.6 volts. disregard the flame test as it does not make any sense.

http://www.boatsetup.com/O2sensor.pdf

My thinking on pumping the ball is that the vst is running low on gas due to a restriction up the fuel line and there is an improper mix of gas and oil in there.

you can also T into the system a vacuum gauge between the engine filter and the lower fuel pump intake,at WOT you should see between 1 and 3"Hg, less usually indicates an air leak more indicates a fuel restriction.
A fuel restriction can be caused by things such as:
1) clogged water sep filter
2) anti-siphon valve.
3) clogged tank pickup tube.
4) clogged tank vent.

if you suspect a fuel restriction, you can trying using an aux fuel tank.

keep us posted and let us know how you make out.

Re: 225 ox66 problems...

I did the vacuum test and it held right where it was supposed to. I ran the engine off a 5 gallon take to eliminate the anything on the boat. I had the VST tank off the engine a couple times and made sure it was clean every time. I also ran the engine with the check valve and water seperator completely removed and still had the problem. I thought it was the VST tank running out of fuel and thats when I hooked up an electric fuel pump to eliminate the 3 low pressure pumps. I thought for sure it was a fuel issue but I have checked everything 3 times on every part of the fuel system.

Thanks
Buddy

Re: 225 ox66 problems...

check the tps. make sure there is a smooth transition through its range.

did you clean the pressure regulator screen?

Re: 225 ox66 problems...

I will have to order the tps harness. I did not clean the screen but I did test the fpr with a vacuum pump. It worked as it should and didnt see any reason to open it up. If the tps is working as it should do you think the screen could still be the problem?

Lets say the fpr screen is clean and fuel isnt the problem. If we rule out fuel I am assuming the problem will probably be spark. What could cause one cylinder to lose spark at wot?

Thanks
Buddy

Re: 225 ox66 problems...

i would clean the fpr screen... it's the only thing in your fuel system you haven't addressed.

check out rodbolts post on one cylinder dropping.

http://forums.iboats.com/showthread.php?t=232590

Re: 225 ox66 problems...

Before I got my TPS harness I just stuck my meter probes in the TPS plug and was able to adjust it.

Re: 225 ox66 problems...

cousinabe: Thanks for the link to that thread. I had no idea that the ecu does not store any codes. This might be the reason the winky blinky is not giving me any info. That persons problem is a little different than mine though. His problem is erratic and mine is dead on every time. Maybe I am not losing a cylinder and it is just a sensor. That would be nice...

Salty Dog: I was going to try this one day but I had to remove a bunch of parts to get to the plug and I got lazy. Hopefully I will order the harnesses soon and I can pin point this problem.

Is it common for the o2 sensor to be out of spec?

Thanks
Buddy

Re: 225 ox66 problems...

ok. do a forum search for the words "surge sensor". there's a lot of good info out there.

Also, the winky blinky does not monitor the O2 sensor. I had to replace one of mine. My symptoms were high fuel consumption. Check the voltage while running. should stay between .3 and .6

You don't want to push that engine with a faulty O2 sensor.
With an O2 sensor failure fuel is fixed rich at low speed and lean above 4000 RPM,same if its contminated.

Like SaltyDog, I used fine wire and tapped into the O2 and TPS connectors while my test harnesses were being shipped.

Re: 225 ox66 problems...

sounds like vst and lp fuel pumps

Re: 225 ox66 problems...

JUSTINTIME said:

sounds like vst and lp fuel pumps

Click to expand...

The lp pumps are new and so is the vst tank filter. I also had the vst tank off a couple of times and made sure it was clean when I put it back on.


A couple of things about the problems that I remembered. When the rpms dropped at wot I could back the throttle off, hit it again and the rpms would go back to to normal for a few seconds before dropping again.

With the smoking issue I could warm the engine up at the dock. Shut if off and turn it back on right away and it would smoke like crazy. Also the bottom of the silencer also had oil dripping out of it when I took it off.

Thanks for all the help.

Buddy

Re: 225 ox66 problems...

yet another good post. i did a forum search on o2 smoke and came up with a lot of good info.

http://forums.iboats.com/showthread.php?t=144262

clean and TEST your o2 sensor. test the output voltage while running.

As for the oil, one thought is that the trim sensor stuck in the down position. When it's down, the internal tank can pump oil to the engine on-board tank, as when you're running. By design, when the engine's tilted up, oil shouldn't be sent to the on-board tank even when the key is left on and the engine is not running. When the sender's down and the key is on and the engine's tilted up, the combination at times will overfill the onboard tank. Its overflow hose routes to the airbox, so if it pumped extra oil into the airbox, it would certainly smoke enough to kill mosquitoes for a while.

Re: 225 ox66 problems...

Thanks for the info. That thread was a good find. I did a lot of searching before I posted about this problem and just came up empty. I guess I have a few things to check out.

test o2 sensor (the right way)
test tps
clean fpr screen
check trim sensor
replace orings, gasket and check valve on oil pump

Hopefully I can get this stuff ordered by the end of the week. I will update the thread as I test everything.

Thanks
Buddy

Re: 225 ox66 problems...

throw the trim sender in the creek and fuggitaboutit.
the trim sender on an OX 66 motor DOES NOT affect the oiling system in anyway.
that was only used on 2.6L V6 from 1990 to 95.
96 and up V6 uses the V76 3.1L control for the PBS system.96 and up V6 use a pulser coil signal to tell the control module the engine is running and oil transfer is allowed.
no run signal no oil transfer via automatic.

I would check the inline check valve and the oil pump shaft seals as they can fail and can be replaced.
max fuel vacum at the lower lift pump is 6" Hg on that engine but I like less than 4" HG.
the resistor was NOT your problem.
the resistor is used to drop pump voltage slowing the pump at speeds below about 1400 RPM, above 1400 or so the pump ground bypasses the resistor and takes it out of the circuit. above 1400 or so you can throw the resistor overboard and save weight.
on the O2 sensor, test the heater voltage at the blue connector for battery voltage with the key on.
test the green connector with the gray wires for a varying voltage between about .35 and about.6 v after a 15 min run above 3000 RPM.
voltage should vary rapidly between .3 and .6 at 3000 RPM.
.1 indicates very lean,.9 indicates very rich and the ECU will alter fuel delivery regaurdless of if its a correct signal or not.
if you dissconect it the ECU will fix fuel rich at idle and lean above 4000 do not run above 4000.
if this engine is anything but a VX225 it incoperates CCS.
means below about 500 RPM all six spark, from about 550 to about 2000 #5 DOES not spark, from about 850 to 2000 #2 does NOT spark.
VX motors DO NOT incorperate this feature.
when I say the ECU on that motor wont store a code it means this.
if the code is active it will register,however if the code is inactive it wont leave a record that it was ever set.
so if at idle my winky is showing code 1 doesnt mean at 4800 I wont be blinking a code other than 1.
this system only shows a code if the code is currently active, if its not you get code 1.
fuel rail pressure MUST maintain at 35 PSI at ALL rpm ranges or something is broke or clogged.
always remember how the PBS transfer system works for the particular engine your working with.
for others reading this always be aware that the replacement 84-89 v6 oil control modules now tap a pulser signal for normal transfer as well as the replacement V4 modules and the V4 from about 2004.
that way they got to eliminate the mercury switch. V6 2.6L from 1990 to 1995 still use the trim sender.
the OX66 system does NOT inject oil into the crankcase like all other yamaha systems. it adds all oil to the VST via a manifold. the check valve simply keeps oil from draining back OR keeps gravity from forcing oil into the VST when sitting.
the only way we can get oil into the airbox on that engine is via the vent line, serveral causes of oil tank overflow the most common is an incorrectly installed engine tank screen.
now a certain amount of fuel/oil spit back is normal and then the fuel will evaporate and leave the oil.
the gray hose on the lower port side of the airbox to the intake should remove this for combustion.
if the hose is dissconected,clogged or missing you will see it drip.
on that engine 225 OX66 any sensor other than the thermosensor and O2 sensor, if they fail out of range OR are dissconected timing will be fixed idle speed increases usually to about 1100 and top speed cannot be reached.
however a loose knock sensor can drive you nuts

Re: 225 ox66 problems...

How much to fly you to NJ and fix my engine?

Thanks for the info. That grey hose on the lower port side of the air box looked to be filled with oil so maybe I should take that off and clean it. The oil tank on the engine does seem to be over the full line some times. That was the initial reason for adjusting the oil pump rod. How should the engine tank screen be installed? What am I looking for?


When testing the fuel pressure I initially had a drop of about ~15psi at wot. The lp fuel pumps were new and after cleaning the vst tank, vst filter and injector screens we thought it was the hp fuel pump. When we replaced that we still had the drop in fuel pressure. The only variable when we did the test after we replaced the resistor was a different fuel pressure gauge. So... either I still have the problem, never had one to begin with or I did something else that I dont remember when I replaced the resistor.


So after that very detailed and long winded explanation you are saying a loose knock sensor is my problem? This is the reason for the 500rpm loss?

Thanks
Buddy

Re: 225 ox66 problems...

not saying anything
your testing it not me.
what I am saying is the diagnostic test lamp will only display a code IF the code is currently active.
over the years I have seen loose knock sensor toss a code and retard timing as well as clogged O2 sensor draw tubes that are knocking in the block.
once running that fuel rail MUST maintain 35 PSI + or - 2 psi or it cant run correctly.
the only time you will see a code 17 is if the sensor is currently detecting a knock.
on the rail, to much fuel pressure and it gets very rich very fast,to little and it gets lean very fast.
the O2 sensor can fail/be contaminated and lean it out above 4000 RPM as well.
with a diagnostic test lamp,a DVM with a DVA adapter,a fuel rail test guage and some system knowledge and the tune up spec guide this motor is easy to check.
basically fuel supply to the VST,rail supply from the VST, then ign producing components and ign Controling components. only thing that can get iffy is checking the injector screens.
if you have access to a merc EFI tester you can actually use it to perform a pressure drop test just like merc used on their EFI two strokes and some mercruiser MPI motors.
what I do is jumper the tester harness,as most time the actual connector is different to the injector,pressurize the system with the fuel pump and toggle the 2ms control signal and observe pressure drop. all six should drop the same.
not real accurate but its all thats offered for on engine flow tests.
to cold in NJ for human habitation
a quick test of the fuel pressure regulator thats not in any manual.
use needle nose pliers and close off the rail return line when pressure drops, you can then "regulate" the rail pressure with the needle nose.
I have seen debris cause the regulator to allow to much leakage yet statically test ok.
like I say, test equipment is nessasary, but so is how does it work and if it dont work knowledge is critical.

Re: 225 ox66 problems...

I cleaned the draw tube a couple times. I also made sure the hole that goes to the tube was clean as well. Hopefully the fuel pressure gauge I bought does work and I am now holding 35psi. I guess the knock sensor and the o2 sensor should be at the top of the list. With any luck I can get a day over 20 to put the boat in the water and hook up the winky blinky. Contrary to belief we do get some nice days in January. The boat doesnt have to be in the water for any of the o2 sensor tests right?

rodbolt: Have you ever seen this exact problem?

Thanks
Buddy

Re: 225 ox66 problems...

have I seen YOUR problem, dunnio. who knows you may be the lucky one that has a failed 3.1L OX66 ECU,. NEVER have I seen one fail,other than the rare one that the oil control module went bad.
odds are in your favor your not lucky.
let me tell you how our normal OX66 troubleshooting goes, check spark,check compression fix the fuel system.
there is no good test for the knock sensor other than checking for a code AT the problem RPM.
the O2 sensor test MUST be made with the boat running at its normal range and with a warmup period of about 10 minutes.
now, have I repaired engines with your symptoms?
more than you and probably 3 others here have ever seen.
you have to remember that not only do I have my own business as a marine contractor I also work full time at a dealership. last dealership I worked from 2000 to 2005 had over 400 boats in the stack and I was not only the lead tech I was the only tech.
for many years a dear friend,recently passed away, was legally blind and had a Yamaha service center, I got to aide him a lot over the years.
luckily he was also friends with most the other dealers in this area.
I also do work for some of the mobile marine guys in this area that either get in over their heads or realize they dont have the training nor equipment to proceed in a timely fashion.
cleaning the draw tube is admirable, did you also clean the sensor itself and test for proper operation?
we dont see it much but always be aware that the injectors screens,6 of them, are subject to clogging as well and give NO codes or indication other than they can run that cylinder lean.
we know what its supposed to do, its supposed to idle in gear trolling at 625 RPM. we know if all is correctly adjusted it works very well. if it wont its broke.
we also know if any monitored code setting sensor fails,except one, that the engine defaults to a fixed 7*BTDC and top speed cannot be reached.
the exception is the thermosensor, if it fails timing is advanced to 7*BTDC at idle and wont retard further but will advance.
high idle but top speed can be reached.
all yamaha sensors can be tested with nothing more than a DVM and a DVA adapter, however the diagnostic test lamp on OX66 or a laptop on 4stroke F motors and HPDI can quickly tell me what hasnt failed allowing me to look for what did.
so the test method you choose is your choice, just be sure you use the correct method for the component being tested.
a bad Tstat on that motor can lead to an idle speed above 900 RPM, runs rich, burns a lot of fuel but otherwise runs. it will display a code 33 all the time as the engine may stay below 113*.
your engine runs with a CCS type ign system. everything normal and NO problems and the ECU sees the temp above 115 you loose spark on *5 until you reach about 2000 RPM AND #2 cylinder between about 850 and 2000.
these are all key troubleshooting features, this motor will mostly test itself if you simply pay attention to what its telling you.