O2 sensor

[bassman3112]

Where is the O2 sensor located on a 2000 Yamaha HPDI 150 H.P.?

[rodbolt17]

under a plastic cover on the upper stbd side of the block.
why ?

[bassman3112]

Want to clean it, motor has 265 hours on it and have some intermittent idle issues. Sometimes after starting, it misses on initial acceleration, and won't smooth out. Sometimes I can turn the engine off, wait a few seconds and it will start up and take off like normal. Have changed in-line filter before motor and drained vst to see if any trash was in there....none. Have read about cleaning the O2 sensor, so thought I would give a shot. Any other suggestions are welcome.

[jb123]

good idea to clean it and tube if you dont use ringfree or equal... but more likely dirty vst filter/plugs/other... even if you drain you arent getting all gunk out... SPECIALLY of you have ethanol in your area

[bassman3112]

ETHANOL.....that ugly word......it is almost impossible to get gas here without it.....I have been using Marine Stabil for fuel Stabilization, had used Yamaha Ring Free for a while, got away from it and am now using Sea Foam as an additive to keep the engine clean and the plugs are new. I am taking it out tomarow to run in the water and see if the situation will clear up. If not I guess the VST filter is next. The see thru filter on the engine looks okay and my in-line spin-on filter before the engine is new. Thanks for any other suggestions anyone might have. Will post tommarows results.

[rodbolt17]

not only is changing the medium pressure inline filter and cleanig the VST filter part of routine maint so is cleaning and TESTING the O2 sensor output voltage.
do you have the service manual?
are you aware that the O2 sensor fedback is not used above about 1500 RPM?

[Tucker]

I didn't know that. Why do they put it in there? I thought it's feed back was used to lean/richen mixture and adjust timing on the fly to a map in the CPU.

[rodbolt17]

O2 sensor has NOTHING to do with ign timing on an HPDI or OX66 motor.
simply a fuel triming device.
on OX66 feed back is used throughout the RPM range, HPDI its only used to about 1500 RPM.
but it has NOTHING to do with ign timming at ANY point.

[bassman3112]

Rodbolt,
Thanks for your replies. I took the boat out Friday afternoon. I had put a can of Seafoam in my gas tank(20 gallons or so in the tank) a few days before and ran the engine for a while on the hose to get the Seafoam all through the system. I cleaned the O2 sensor the best I could....did not seem to be really carboned up, but it did need some cleaning. When in the water Friday, the motor started fine...like it always has. After a short warm up, I put it in gear and as I was throttling up (below 1500 RPM), it missed as before, but not as much. I shut it down for 10-15 seconds, started back up and it took off fine and for the rest of the day it ran fine. I did notice a better throttle response on takeoff and throughout the speed range all the way up to 4500 RPM. Can SEAFOAM have solved my problem????
I will know more the next time I go out. I have purchased a Manual on line, but they had to backorder it. You guys have been a big help!!!

[rodbolt17]

doubt it.
all the O2 sensor does on that HPDI is fuel trim.
what I would do is get the manual then monitor O2 sensor output voltage.
its the ONLY way.

[Tucker]

Well it didn't do it by itself, probably some carbon build up somewhere else. Seafoam is a 2-cycle engine's best friend. Tons out there documenting that. Seldom embraced by the pros though, they stick with the OEM products.

[rodbolt17]

me thinks someone doesnt understand how a two stroke direct injected outboard by Yamaha actaully operates.
seafoam isnt any different than power tune,ring free and some others.
however above 1500 RPM on the HPDI you can toss the O2 sensor overboard.
if anything it could have cleaned some debris from various fuel filters, there is like 12 filters under the hood in various places, only about 4 are field servicable.
typically with a two stroke it will blow a piston long before any snake oils can help.
DFI yamahas lubricate the crank and pistons with oil coming in with the intake air charge.
the rest of the yamaha line up uses fuel,air and the oil.
its also why on oil injected yamahas a blown fuel pump
diaphram can and will toss a connecting rod.
trust me, carbon isnt your issue and 20 gallons on a 150 isnt enough to do much.
I have seen O2 sensors that the debris screen looked ok and the tube clear that did not work even after claening and I have seen some nasty buggers that still worked perfect.
the ONLY, get that? ONLY way to tell is to MONITOR the O2 sensor output voltage.
NO OTHER WAY.
I have seen them NOT work brand new out of the box on vairous manufactures I have worked on since 1975.
nice thing, HPDI, unlike OX66 EFI, the O2 sensor wont smoke a piston.

[bassman3112]

Thanks Rodbolt,
As soon as I get the Manual, I will check out the O2 sensor output. I am glad that the O2 will not smoke a piston!!!
I wonder why Yamaha has to have so many filters??????????