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.