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  1. #1
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    Post Yamaha ox66 225-need some help

    I'm at my wit's end with this motor. I've done tons of reading, and can't figure out a problem I'm having. I'll go through what I've done, my plan, and am open to any and all advice. Motor is a 2003, vx225tlrb.

    This started with a loss of RPM and mph on top end. I lost about 500rpm, and maybe 8mph. It would only do it sometimes, but what I started to notice, is that if it had a slight miss coming out of the hole, it would only run about 54-5500 rpms. It has progressively gotten worse. It's starting to miss more coming out of the hole, and like always, if it misses coming out of the hole, it will be slow on top end. To the point where it would only run about 50mph, the boat usually runs 72-73.

    Here's what I've done.

    -replaced all LP fuel pumps
    -replaced VST filter and motor filter
    -replaced fuel lines from tank to motor (I did end up with a screw ran into the fuel line, noticed it when I replaced the lines) and primer bulb
    -checked tps- within spec- I took it out today, took voltage readings, all seemed right; though it only missed once and I happened to not have my meter hooked up that one time
    -replaced 02 sensor with the generic NGK one-soldered by car audio professional, I think it's good; edit: I have flame tested the 02 sensor, it checks out per the manual
    -checked voltage on HP fuel pump, which seemed fine
    -unplugged shift switch (I know this cannot be the cause because it missed with it unplugged)
    -also, when it was missing last week, I pump primer bulb while it was missing and it did not change
    -spark plugs were changed when I bought it, they look good, but I do have another set, I plan on changing this week

    Today, I was unable to accurately measure fuel pressure. I rented a guage from Autozone, and it read 8 psi. There's no way this is correct, the motor was turning 5k rpm and running perfect, there's no way it would run that well with only 8psi.

    So my plan from here
    -accurately measure fuel pressure
    -maybe send my injectors off to be cleaned; now cleaned, guy said they looked pretty good and they were not the cause of my problems
    -replace anti-syphon valve and check/clean pickup tube; anti-syphon replaced, found a bunch of crap in the tank
    -check spark quality (would like more info on how to go about that)

    The frustrating part is it doesn't do it all the time. When it misses it does it pretty good coming out of the hole, and I loose a bunch on top end. Today, I made 20-30 pulls, it only missed twice, both back to back. I do have the full shop manual, and have been working through it. I also am currently trying to get my hands on a winky blinky harness to see if it says anything. Like I said, I'm open to suggestions.

    I'm not the best mechanic, but have been working on things for a while. When I bought this boat in July, it immediately overheated first trip out. Turns out it had a burned up exhaust tuner. I was able to replace it and all the parts that go along with that without a hiccup. This is much more frustrating, and I'm at a loss. Thanks so much for the help, Clayton.
    Last edited by TwinStick; 06-05-2019 at 09:33 AM.

  2. Member
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    #2
    I would check the compression in each cylinder just to make sure it’s good first. Head gaskets in that motor can start to leak and cause issues. Could be a leaky gasket. My guess is you have a fuel issue. Buy a fuel pressure gauge. They aren’t expensive. It should be a steady 35 psi from the hp pump. Could be the fuel regulator, but I’ve never had to mess with that on mine, so can’t comment on how to test. Check the manual for how to test it, or maybe someone else knows.

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    #3
    Mine did that i have same year motor. Check VST tank if pressure to high should be 35psi. My pressure was 75 psi. I ordered new pressure regulator. Problem solved.
    Russell Winneberger
    2002 Stratos 20 XL
    ColorVision Painting

  4. Member
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    #4
    I plan on checking compression for completeness sake, but I don't think that's the issue.

    One thing I did note yesterday is interesting tps readings at wot.

    I checked it at the house without #1 linkage attached. I got 0.49 with butterflies closed. I got 4.9 at wot. On the lake I went to wot and you voltage I think went to 3.9. That seems low to me. I was still getting about 58-5900 rpms.

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    #5
    If the TPS shows smooth change in the voltage reading as you move it it should be ok.

  6. SEE YA!!!!!!!! DLAB's Avatar
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    #6
    http://www.bbcboards.net/showthread....hlight=Gremlin

    check my thread out from years ago. That one little screen was my issue. And while they normally don’t go bad, I do have a known good ECU I could send to you to try, and buy if it fixes your issue. I’ve sent it to a few others in the past to troubleshoot, however it never was an ECU issue...

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    #7
    I read your thread a little while back and it prompted me to pull my vst back apart. That screen is not there. I'm not sure if there was trouble before and it was removed or if it never came in it. I put it back together without adding that screen in.

    Thanks for the offer in the ecu. If it comes down to looking like that is it I'll definitely give you a shout

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    #8
    Does it ever cut out when on plane?

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    #9
    Sometimes it will. If it misses bad enough out of the hole it will. Most of the time it just misses coming out of the hole and loses rpm up top

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    #10
    I pulled my injectors out today to have them cleaner. I also pulled my pickup and anti-syphon valve. Both look really good, buit I'm going to go ahead and replace the anti-syphon valve. But, I was looking down in my tank and I noticed this stuff. Had to go fishing for a while, but finally got it out. Hopefully there's nothing else in there. If I didn't have between 1/2-2/3 of a tank I think I'd go ahead and pull it. I'm not sure if this is causing my issue, but regardless it's not staying in my tank.


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    #11
    Did you pull the tube in the block at the O2 sensor and clean it? If it is caked in carbon, it is easy to miss it. If that is plugged, whatever you do with the O2 sensor won't make a difference. The other outside chance is the fuel pump relay. When that goes, you will get random cut-outs and hard to restarts. The fuel pump relay problems will appear random. Hard to tell, but since you didn't mention cleaning the tube, that could be it.

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    #12
    Sorry, should've mentioned it. I did clean it. Not that I really think this will help, but I'm having the injectors cleaned tomorrow.

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    #13
    I have a question about fuel pump voltage, when I measured fuel pump voltage I had about 9.5 volts at idle. As the motor increases in RPM, so does the voltage. When I go to full throttle voltage goes to 12.5. It is a progressive sweep from 9.5 to 12.5 though. Does this seem normal? I kind of thought it would have 12.5 volts all the time. Again, thanks for all the help.
    Last edited by TwinStick; 06-03-2019 at 11:11 AM.

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    #14
    Quote Originally Posted by JoeFriday View Post
    Did you pull the tube in the block at the O2 sensor and clean it? If it is caked in carbon, it is easy to miss it. If that is plugged, whatever you do with the O2 sensor won't make a difference. The other outside chance is the fuel pump relay. When that goes, you will get random cut-outs and hard to restarts. The fuel pump relay problems will appear random. Hard to tell, but since you didn't mention cleaning the tube, that could be it.
    If it was spic and span once done, you should be good there. Usually when you have drop offs at WOT, it's something with the O2 sensor. Since you said that it is cutting out on plane, there is an outside chance that it's the fuel pump relay. Once that gets off, it throws random weird stuff that seems like you'll never be able to figure it out.

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    #15
    Edited original post, 02 flame test volts in spec, though it had 5ohms which is the same as the one it replaced. The manual does call for 100ohms, but I only ever see people talk about checking voltage. I will hook up a fuel pressure grade this weekend, but at idle I put my tire gauge on it and it registered about 36.

    I went back through the vst. I did find the regulator screen. It was in the vst side not the regulator side. I cleaned it, but it wasn't too bad.

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    #16
    I'd try running it on an aux tank. Was pressure steady even while missing?

  17. SEE YA!!!!!!!! DLAB's Avatar
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    #17
    Have you done a compression check yet?, Bore Scope? I lost power on my first OX66 years ago and couldn’t figure it out. Turns out one of the cylinders had a hairline crack that would open when it warmed up.....

    lots of gremlins that could happen, but check the compression after the engine is warmed up for a change and see if you see a dramatic drop in one

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    #18
    Well, I've got to suck it up and tell y'all what I figured out yesterday. I really can't believe it and have been kicking myself. I've spent so much time researching, testing ohming, nothing.

    Went out to the lake yesterday, had my dad driving. Fuel pressure was steady at about 35. Everything checked out. Then my dad started to lug it, and it started missing. Fuel pressure was constant. It kept doing it, so I determined it couldn't be a fuel issue.

    I decided to just go ahead and throw another set of plugs in right then and there on the water. It never missed again. I'm going to put another set of wires in it just because, but I can't believe I didn't do this first. Major lesson learned for me. I really appreciate everyone's time and help with this.

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    #19
    Don't feel bad I did the exact same thing last year and after i couldn't find it I took it to my mechanic and he, chased ghost to the tune of a few 1000 $. Spark plugs ended up being my issue as well, They looked good but 1 ended up being the issue.