2006 HPDI 175 RPM issues

[BassinTN]

I have a 2006 HPDI 175 (VZ175TLR) with 78 hours on a 2005 Xpress X19. I bought it 3 years ago with 32 actual hours. The boat was owned by a 74 year old man and he never used it. 2 years ago @ 40 something hours I replaced the VST filter, high pressure filter, and electric fuel pump (aftermarket). I've hit 64.7MPH @ 5800RPMs and it typically runs 63 when it's running right. Throughout the day it will hit 5800 on one run, 4800 the next, 5200 the next, 4000 the next, and so on. Some times at WOT it will surge and never hit 5800. I only run non ethanol 87 octane with Star Tron fuel treatment and Ring Free. I've hooked up the laptop with YDS (bought on eBay) several times in the driveway on muffs and it always shows everything normal. I suspect a fuel delivery problem but that's just a guess. I'm thinking I need to run a cable to the console and run it WOT on the laptop and may try that this weekend. Is the YDS sold on eBay reliable? Are the aftermarket fuel pumps reliable? I keep hearing the small block HPDIs are great outboards, but this one has never really run right for very long. It's nearly impossible to get in to see a Yamaha tech at any dealer I've called locally. Any ideas would be greatly appreciated.

[skeeter21ohio]

What's plugs look like after running it? Could tell if got fuel delivery issue in certain cylinder

[BassinTN]

What's plugs look like after running it? Could tell if got fuel delivery issue in certain cylinder

That's a great idea and I haven't thought of it. I'll try to do that this weekend.

[1ranger487vs]

Does that engine have a 02 sensor

[skeeter21ohio]

Any updates?

[ChadG]

We had the same issue. Put a new o2 sensor in and problems are gone for now.

[BassinTN]

We had the same issue. Put a new o2 sensor in and problems are gone for now.

Thank you for the info!

[BassinTN]

Any updates?

Not yet. I was off Thursday and Friday but I got a tip on a hot crappie bite a mile from the ramp so I fished both days and barely ran the motor. Priorities!