[GWDolphin25]

Hi everyone!

I'll thank everyone in advance for posting answers and questions in these posts. I find them very helpful. I am not a certified Tech so forgive me if I use incorrect terms.

I have this HPDI with a freshly rebuilt powerhead. The injectors were ultrasound cleaned and tested. Spark plugs are new. The engine oil lines were primed correctly and everything is injecting as it should.

The engine fired up and idled beautifully for about 10 minutes so I shut it off. I then got the Yamaha Diagnostic Software and plugged the motor up to the computer to see the engine monitor and run diagnostics. When I did that, the system showed everything to be normal but now the engine missed badly and I found that the #2 and #3 Cylinders were not firing. The monitor would go to YES as it cranked and did the initial fire then it would go to NO, stay at NO and miss, eventually stalling. I checked and changed the coils and cables and checked all connections and spark plugs. Everything seemed normal.

I don't know where to go with this and any help would be great. Thanks!

[GWDolphin25]

I Googled and found out after this post that the HPDI 250 drops out the #2 & #3 at low or trolling rpms. Excuse my ignorance! I still think the engine is idling too rough for me.

This motor threw a rod after over 1600 hours. I guess this was one of the good ones...or one of the lucky ones. It's run over 1100 hours in the 3K-4K rpm range and about 350 at about trolling speeds. Just some info.

Thanks again.

[rodbolt]

your close,still no seegar.
at idle in nuetral the Z motors drop cylinders 2-3,in gear ALL 6 hit regaurdless of engine speed until the rev limiter gets you.
during cranking all 6 cylinders fire until the engine is running then the ecu looks at the shift switch position and determines is it in nuetral.
if ya really want to watch something silly,throttle it up in N and you will see 2 more cylinders drop off as engine speed approaches 1800 or so.
whats amazing is the amount of folks,both online and in the shop,talk about it will hit 4000 RPM in Nuetral on 2 cylinders.
however I can never see a reason to throttle up an EFI or DFI motor in nuetral.