OX66 problem-Please advice!

[fishinAK1]

Hello all
So I am having a problem w my 2005 200hp OX66. I no longer can get above 4600 at WOT (used to be 5500) and my fuel consumption is even worse (now 17 gal/hr was 12 gal/hr).
I suspected a stuck injector. So they were sent into Brucato FIS. he cleaned and recal to spec (they were ALL flooding).
I also suspected O2 sensor, I removed and cleaned that. do this every spring anyway. The dog bone was caked with carbon, as usual, and there was wet oil in the tube.
I also replaced spark plugs as all were wet and BLACK. especially the top 2.
other maintenance/checks etc.
-clean VST and filter
-new thermostats
-new LP pumps
-new PCV valve

After all this, I took for a rip yesterday. SAME symptoms. after only 20 min of running the plugs were black and kinda wetish looking. again, especially the top 2.

I am really assuming my O2 sensor has failed. and needs to be replaced instead of cleaned.
What do you guys think? Sound like a failed O2?

THANKS!!!!

 

[SkunkBoat]

Its possible one cylinder is not firing. i would check spark. Look for bad wires. Especially look for bad/cooked connections to the coils.

Did you replace the filter screen that is mounted at the pressure regulator? If your injectors were dirty then that one is dirty.

 

[DennisG01]

Do you have a service manual? I don't have mine handy, but there are tests in there that you can run on the O2 sensor with a DMM and they are very easy to do.

By they way, I run Startron and RingFree religiously - my dogbone actually stays quite clean. So much so that I haven't even pulled it and checked it in the last few years because before that, when I did pull it, it never needed cleaning.

 

[fishinAK1]

Thanks guys. I haven't checked for spark yet. I will this evening, after the sun sets.

I do have a manual, but it doesn't show the O2 sensor test. I have read that you need a special harness for the test. there is also a flame test, I tried that. but seemed inconclusive.

Wow, that's amazing that yours is so clean Dennis! Like I said I have been cleaning mine almost annually for the past 10 years and its almost solid with carbon every time. maybe this is an indication of a slowly failing O2 sensor.

Also, I attempted to pull the filter on the fuel pressure regulator, but the 2 screws are so corroded on there rather than risk rounding them out, I decided to just test the fuel pressure instead. AND when I had the injectors cleaned the filter baskets on the injectors were "spotless" (just running rich). which makes me think the regulator filter is also clean.

I don't have a fuel pressure gage. and I don't want to risk virus going out to buy one yet. Ill asking if friends have one to borrow first. So should be 35 psi off that shader check valve all the time running and just key "on" right?

Thanks so much and I hope you and all families are healthy!!

 

[Andrew93]

I was gonna guess low pressure fuel pumps but you replaced them. When I had a bad O2 sensor I could not get the boat to hold a steady RPM, it would drift all over the place. Being so expensive I replaced with the automotive one and spliced the wires to rule it in or out, when I figured that was it I replaced with the expensive OEM one.

Also there is a small basket filter on the fuel pressure regulator on the return line to the VST tank. I remember reading awhile ago on THT of some strange symptoms that was tracked down to that, but I don't recall what they were.

 

[DennisG01]

Alaska, I attribute the clean sensor/dogbone to the RingFree. The last time I checked it, I took it to the local Yamaha dealer to get the right gasket. The guy took one look at it and said "You must be using RingFree. No one's is ever THAT clean without using RingFree". If you're not currently using it, I'd start!

If you have the Yamaha service manual, it's definitely in there. I can check later. I've done the flame test - I've also read that it may/may not be a definitive test, but I'm not really sure one way or the other on that.

 

[seasick]

It is probably not the LP pumps. If they are weak, your motor will get to a speed and then die off, then rev up again as the VST tank refills.
LPs are probably OK

Note that at low revs, 2 cylinders do not fire ( 3 and 6 maybe?) so if you check for spark you won't see it on all cylinders at low revs (under 1100 or so). To test spark use a spark tester tool, do not run the motor with the plug wires disconnected. You can fry the coils.
If the O2 is bad or clogged the motor will run rich.(usually)

There is a simple way to test the O2 sensor. It has to be out of the motor. The sensor has 4 wires, 2 are for the pre-heater coil. I cant remember the colors but they might be thicker than the other two.
The heater wires should have some resistance when tested with an ohm meter. If the heater coil is bad ( kind of rare occurrence) the motor may have issues when cold. Once it heats up, it makes no difference ( so that is not your issue)
The other two wires are the signal from the actual sensor element. Connect a volt meter set to a low voltage scale and heat the tip of the sensor ( just the tip!) with a propane or butane flame. Do not use acetylene. As the tip heats up, the meter should read increasing voltage. Don't overdo it. If the voltage changes, the sensor is probably fine.

Have you checked the oil pump linkage? If out of wack it will add too much oil to the gas.
I also suggest a compression test. With all that buildup, you may have a problem with the piston rings. I also suggest that you check the high pressure fuel pump pressure both at idle and at speed ( probably need two people for that. I also don't remember the pressure spec. 32 psi or so sounds about right. Your service manual will have the number. The key item is that the pressure should not vary very much at all.

 

[DennisG01]

I typed this in your other post about parts - just copying and pasting to this one:

I'd assume your manual should be at least mostly the same as mine. Afterall, 02 sensors didn't change. But go to the electrical section (Ch. 8 in my book) and you'll see it listed. But quickly... resistance should be less than 100 ohms between the white wires. Voltage should be less than .3V with a running and warm engine at idle : (B/W (B) - Gy). That's exactly how it is listed - I'm not at the boat to make sense of that, but it may mean between a ground and the Grey wire. But look at your manual - see what makes sense to you.

 

[fishinAK1]

Thanks guys.
SeaSick. I did do the flame test. And it did seem to fluctuate volts when flame was applied. Albeit, seamingly very sporadic.

Dennis,
I did fine that section in the manual. I guess I have a hard time understanding it tho. I assume I have to perform this test w the outboard running? Then how do I reach the bare end of the wire leads that are inside a harness tucked behind the CDI?
Any advice on that test greatly appreciated!

im gonna try to find a fuelpressure tester today and check that. BUT seems like I’m getting prenty (too much) fuel. So to me, a bad pump seems unlikely. Manual says 35 psi. Does that mean with key on after fuel pump kicked on?

Thank you so so much!!

 

[seasick]

Thanks guys.
SeaSick. I did do the flame test. And it did seem to fluctuate volts when flame was applied. Albeit, seamingly very sporadic.

Dennis,
I did fine that section in the manual. I guess I have a hard time understanding it tho. I assume I have to perform this test w the outboard running? Then how do I reach the bare end of the wire leads that are inside a harness tucked behind the CDI?
Any advice on that test greatly appreciated!

im gonna try to find a fuelpressure tester today and check that. BUT seems like I’m getting prenty (too much) fuel. So to me, a bad pump seems unlikely. Manual says 35 psi. Does that mean with key on after fuel pump kicked on?

Thank you so so much!!

As soon as you turn on the key the HS pump runs and you should see pressure in the fuel line test fitting. The pressure in that line should be constant. The low pressure pumps keep the VST tank full and that fill is controlled by the float and needle valve in the VST tank. As you probably aware, the LP pumps only work when the motor crankshaft and other rotating parts are actually rotating
The high pressure pump pulls gas from that tank and pumps it to the pressure regulating valve which in turn feeds the high pressure fuel rails. The pressure regulating valve is purely mechanical. There may be a fine mesh screen in the output side.
If you saw voltage in the range Dennis mentioned, you don't need to do his in-place test
Harbor Freight sells a fuel pressure test kit. It really is a cheap set of fittings, hoses and a gauge but it does work ( at least for a while)

 

[fishinAK1]

Ok. I found a fuel pressure tester. and about to go do a check.

SO pressure at that check valve should be 35.6 (according to manual). BUT does this mean with key in "run" position but not started AND when outboard is running?

 

[seasick]

Yes of course. If it didn't have pressure the motor would never start

 

[fishinAK1]

Haha of course. But should it stay around 35, throughout throttle range?

 

[seasick]

Yes.. It shouldn't vary much at all.

 

[DennisG01]

Thanks guys.
SeaSick. I did do the flame test. And it did seem to fluctuate volts when flame was applied. Albeit, seamingly very sporadic.

Dennis,
I did fine that section in the manual. I guess I have a hard time understanding it tho. I assume I have to perform this test w the outboard running? Then how do I reach the bare end of the wire leads that are inside a harness tucked behind the CDI?
Any advice on that test greatly appreciated!

From what I recall about the flame test, that sporadic fluctuation is what is expected - given the drastic temperature changes from he torch.

The resistance test is done with engine off. The voltage test would be done with it running. I never got around to having the need to do the running voltage test, but the SM states using a test harness which would T into the quick-disconnect plug. You could backprobe (I thought you could reach the connector?) or even probe into the wires and then cover the holes with some high-temp RTV. I'm generally not a fan of poking holes in wires, so I would ONLY do this into the O2 sensor's wires - not the actual wiring harness.

 

[fishinAK1]

So for the resistance test, do to test between the black wire and grey wire (they clip above the CDI) or the 2 wire w blue harness that run into the fuse box?
Thank you!
...also if you have time Dennis, I posted today’s update in the “0X66 LP pumps” thread. Curious if this sounds like an O2 issue to you.

 

[seasick]

It is easier to test on the workbench but you need a decent connection to the pins of the connector. Two sets of hands may be needed. One to hold the connections tight and the other to heat the O2 tip.
I am nor really worried about the resistance test for the pre-heater coil since once a motor is warmed up, it isn't needed .
By the way, the two threads have info common to both issues and is quite confusing to my old brain

 

[Sparkdog118]

It is possible that the intake manifold gasket between cylinder 1 and2 could have been damaged when the injectors were dumping. This would cause a loss in vacuum between 1 and 2 making them run rich. Also possible a reed gasket may also have been damaged.

 

[georgemjr]

Seasick made some good points. I believe that the O2 sensor is not supposed to make a difference at higher RPMS?, only at idle/low rpms. Anyone have intimate knowledge of that? As Seasick said, that motor intentionally drops 2 cylinders at idle. Could the switch that drops them be defective and therefore, they wouldn't kick in at higher RPMs? If so, those cylinder's spark plugs would be very black while the other 4 should still be clean. If all 6 are fouled, then I might suspect too much oil being added as was mentioned. Is your oil consumption high? I use ringfree religiously and have had the CO2 sensor and dogbone issues myself. My solution is to get away from Yamalube, as I believe the oil does not burn as clean as a synthetic version.