Yamaha HPDI crazy troubleshooting story

How can you have compression, spark, fuel all at the correct time but no power? I explain in this video. You will be surprised by the reason.

[@stevemagnuson7051]

Wow, what a story! I own an ‘05 HPDI 250 which I purchased with a bad piston. Rebuilt with pistons supplied by Hydro-Tec. I am also an A&P mechanic so I maintain meticulously. I could feel your frustration before you found the piston issue. “Good find” as we say in aviation maintenance!

[@billreynolds3539]

Thanks for sharing this Very thorough diagnosis. It helps me understand the relationship of all the systems.

[@jolssonusa]

Many thanks for sharing this unbelievable story. I am impressed by how you went through everything step by step to finally arrive at the craziness of installing the wrong piston - jeez who would think of that!!!. I have made a couple of rebuilds of Optimax and I love it. I am not trained but I guess pretty mechanically inclined. Your story tells me to take nothing for granted on older motors. Many thanks

[@dnovelle1]

Amazing story!! You were very lucky you the engine wasn't damaged.

[@ct1762]

i would've almost instantly thought of twisted sleeves or an intake blockage. if its getting plenty of fuel no use going further there. same with spark. thats crazy those morons where so sloppy. every rebuild i do i mark each piston with a red sharpie and an arrow as the markings on the pistons are hard to see. glad you got it sorted what a pain!

[@outdoorlyf]

Very informative. Thank you

[@Carlos_1983]

Great job! I think you will out a ton of hours on that motor with your knowledge. They are great motors if you understand them!

[@willhibbard3137]

Thanks for sharing and taking time to find the one problem. Mystery engines can be challenging. Just when an experienced marine tech thinks they have seen everything the next lesson is on the way. I call these bush engines... Bottom line is when an engine wont perform correctly it's generally one simple malfunctioning item complicated by a plethora of misdiagnosed remedies performed by novices who attempted to cross over to perform marine service specialist operations. Generally speaking these guys are under the influence of some form of self medication in light of they are wanting to relax by spending time on water. They generally create many more malfunctions to where the boat is parked in the bushes because of wrong or incorrectly installed parts.

[@ChrisJones-nt1sy]

I have the same motor except its a 300. Fresh rebuild last year, destroyed a stanless prop last weekend at 5700rpm and got a wicked vibration and slight knock that comes in at 3k and stops at 3300. Still runs top notch but not sure if it's a piston or lower unit issue. Dropping off at HydroTech tomorrow. Lake of the Ozarks boat.

[@ihtfishing4726]

Good place to have it checked out. 👍

[@Anthony-du3he]

Wow

[@chucknubern8549]

Had a 05 act up this weekend. Plugs a day old , running it in a tourn about 55 mph when i felt what I can only describe as a slip then a loss of power. Now idles a lil rough and won’t get on plane. What should I check in what order to diagnose? Any help is appreciated

[@ihtfishing4726]

It sounds like it could possibly be the neutral switch that makes the engine only fire on 4 cylinders when in neutral at idle. I would probably start by connecting a water source and run it while monitoring for a change in engine sound between neutral and in gear. Mine idles rougher when in neutral for sure. Also, I would pull the plugs back out and see how they are burning and run a compression check at the same time. Go back to basics, do I have compression, fuel and spark everywhere first.