Poor 150 OX66 performance

[1PairOfChoppers]

Looking for ideas on why my 2000 VMax 150 OX66 is running like crap. Doggy out of the hole and occasional engine surging.


Took the boat out after a thorough cleaning of the O2 sensor that was completley plugged with carbon. The sensor bench tests good. I also cleaned the spark plugs as they appeared to have been running rich due to the fouled O2 sensor. Could not get above 4200rpms and the more I ran this motor, the worse it ran. I felt the pee stream for temperature after making several runs and felt luke warm.

Once I got it home again, I pulled the plugs to find the bottom right plug to be completely fouled and the bottom left to be burning a little rich. The top and middle plugs appear to be burning better, more brown that black. These plugs are practically new but have been run while the O2 sensor was plugged and the motor running rich. I also tested the thermostats, they opened at 120F (50C) and are clean. After the 10 minute trip home, the heads were hot. Alot hotter than the pee stream.

My question, could I have something else going on other than plugs at this point? I will put new plugs in and hope that cures it.

I also checked the poppet valve. Couple pebbles of sand that may have kept this valve open. Really clean compared to the poppet valve pics in the sticky post here.

Another question, can a stuck open poppet valve cause poor engine performance?

Any input will be greatly appreciated, thanks!

[Hamfisted]

When you cleaned the O2 sensor did you also clean the "Dog Bone" orifice tube that passes exhaust gas between the block and the sensor? You have to pull the O2 sensor mounting block off and the dog bone is under that. Pull it out and you'll find that it too is covered in carbon.
You'll need a new high heat gasket from the dealer ($15).
What kinda shape is your Racor filter in? The surging might also be from a filter blockage. But I would clean the O2 sensor's Dog Bone tube first.


Mike

[1PairOfChoppers]

Hi Mike,

Yep, the entire path from the block to the sensor was plugged tight and I cleaned it well. Is there a place inside the block beyond the "Dog Bone" that could be blocked? I think I would have to take the head off to see and would rather avoid doing so unless necessary.

I used orange high temp RTV gasket sealant for the short term until I get my hands on a new gasket. Looked like the last person to service the sensor did the same thing.

I don't have a Racor filter but have the stock Yamaha water/fuel filter shown here:

http://www.boats.net/yamaha/pa...90929

The water float ring is on the bottom and no debris the naked eye can see in the filter. I will replace the filter since I don't know when it was last changed. Bought the boat used last year.

If the plugs don't cure it, it may be a bad coil or fuel pump(s).

Thanks!

Guy

[Hamfisted]

There's a specific warning against using any kind of RTV silicone sealant around an O2 sensor. Fumes from the silicone can contaminate the element in the sensor and render it useless. I don't know if it can be cleaned off. Did you soak the sensor in Sea Foam or some equivalent cleaner? Did you test it with a multimeter and propane torch afterward and it passed?
That underhood fuel filter is not worth a crap for stopping water. Install a Racor. The filter inside the VST could be clogged as well. You can pull the VST off and remove the screen filter and spray clean it with some Chemtool spray (Walmart). How old are the mechanical fuel pumps? Can you pump up the primer ball firm?


Mike

[1PairOfChoppers]

I figured it would be OK since there was already some type of RTV sealant used when I took the sensor out. I wouldn't imagine that too much harm could happen. I would think the dog bone would seal out contaminants considering how it fits inside.

I did soak the sensor in Ringfree and then Seafoam to speed the process up. I tested my O2 sensor with a digital Fluke meter. Heated the tip with a butane lighter and got a .1v response rather quickly. I will restest with a propane torch to see if I can get more volts (up to 1v). Ohmed out the heater side of the sensor and got a 4ohm reading. The normal range is 2-14 ohms.

I picked up a new fuel filter over lunch. I understand that it doesn't block water only separates some and will show presence of water by the floating red ring.

Then mechanical fuel pumps to my knowledge are original. I will test the primer bulb tonight.

Thanks!
Guy

[1PairOfChoppers]

Thanks Mike for your help, your time is greatly appreciated.

I put in a new fuel filter, new O2 sensor gasket, and 6 new plugs. I cleaned all visible traces of the RTV and cleaned everything related to the sensor with Seafoam. Hopefully I didn't cause any harm to the sensor. I tested it again by leaving the heated side connected, turned on the key, and checked voltage. Got .35v with just the heater and .8v with a propane torch. Then blew on it to cool briefly and voltage dropped immediatly. Very responsive.

Took it out for spin tonight and it's running great! Hopefully it stays this way. I checked the bottom right plug when I got home and it burning perfect. Not too rich, not too lean but just right. :)

I'm thinking since the plugs were running too rich before due to the carboned sensor that with the new plugs it should be fixed.

I couldn't get the primer bulb to get hard and could feel/hear fuel flow through. The check valve may be shot. I'm going to replace this as well since they're cheap.

G