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Yamaha 250 VMAX HPDI surges at midrange only
Hello Gents, Completely scratching my mechanics head as well as well as mine so any help would be appreciated. This 2006 2 stroke engine throws no faults when connected to Yamaha diagnostics. The problem is that the motor surges at the midrange RPM's between 3400-3900 RPM's only. She runs fine and throttles up to & cruises perfect up to 3300 RPM's with no problem. She struggles and surges at 3400 thru 4000 RPM's and does not want any part of this RPM range but opens up and runs like a scalded cat above 4100 RPM's all the way 'till max RPM's of 5600 RPM's and 60 mph+..., no problem. This surging problem started very slowly at first, in fact it was barely noticeable and would only pop up occasionally and very faintly after several hours of running at that midrange RPM. Then about 10hrs ago it started getting progressively worse & worse over time. The one indicator of what may be the problem is that at cylinder #2, she oil fouls that plug after a brief 15 min run ( brand new sparkplug) but all of the other 5 plugs are clean. She starts up fine and idles fine. All filters and screens replaced incl. the main Yamaha 10 micron, regular spin on clear water sensor filter, VST (in unit) filter, & mid level cannister filter. The high pressure pump is reading 980+ at all RPM's, VST Schrader (American) valve at about 45lbs during all RPM's. I changed out the #2,#4,#6, injector driver, no change. I ran a scope in cylinder 2 and it looks great, I ran a scope and the reeds look fine with no distortion. I changed injector #2 and it ran a bit better but still surging. Changed the mid level VST fuel pump and ran the same outcome. Emptied the fuel tank and re-filled with REC 90 ( always ran REC 90) and same surging. Switched out the neutral shift switch.., same. I checked the spark at #2 and sure enough, good spark. Full tune-up incl. plugs etc., same problem. Compression at 120/122 on all cylinders. Changed the battery ( even though HPDI does not suffer the OPTIMAX battery voltage sensitivity), same problem. What is really frustrating is that it's only at that mid range that we get the surging so a lot of the typical diagnostics don't apply here. I am tempted, to completely change out the spin-on clear water/filter assembly since I've read so much that O-ring on the spin housing tends to warp but the fact that this is ONLY a mid RPM issue which would indicate that this (vacuum leak) is not the problem. Bad coil, usually not applicable at midrange only but who knows. I'm wondering if maybe I have a corrosion issue on the header plate but that doesn't make sense. This motor has less than 700 hrs and runs strong it’s only that mid range surge that is a making me mental. Thanks in advance for any help.
Last edited by JTquint; 10-24-2021 at 02:17 PM.
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This may sound crazy but have you tried a different prop. Could the hub be slipping in the prop.
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It’s an OFX4 solid hub. thx.
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Switch the #2 coil with another cylinder and see if the problem moves to that one.
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I would have all your injectors serviced and see if that helps.
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Changed out coil 2 &. Better but not gone. Going to try to swap out the bank and see.
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Check the fuel prime bulb. When mine does that stuttering at mid range, if I go and squeeze the fuel bulb, problem is resolved for nearly the rest of the day.
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Id try running it on a separate fuel supply.
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I had similar problem with my 01 ox66 225; Not sure if HPDI has O2 sensors, but that was part of the cause with mine. The other thing that totally fixed issue was I had some dirt in the Poppet valve. Easy to remove and clean, but a pain to put back in. There were threads on this forum going back about ten years where a lot of guys were having the same issue. Hope this helps.
Old Skeeter
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“​There were threads on this forum going back about ten years where a lot of guys were having the same issue. Hope this helps.​’
Thx. No O2 sensors on this motor & problem poppit valves manifest as temperature issues. I’m going to go back in the BBC to see if I can find some of these “surging” threads. Also, has anyone ever replaced a faulty ECM on their HPDI? Seems that everything I’ve read on these engines says that the ECM’s are bullit proof but I’ve run out of possibilities. Thanks again.
Last edited by JTquint; 11-30-2021 at 07:37 AM.
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Have you tried replacing your injector relay in the fuse block? Mine went bad and at first it would only surge at those rpm ranges, then it became hard to start. The relay is fairly inexpensive and easy to replace.
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Thx Bobbyf. I replaced the injector driver for cylinders 2,4, & 6 - port bank-. Did you get an error code from the software which indicated that the injector relay was bad? I have no problems starting up at all, the engines fires right up & only fouls cylinder 2 plug.
Last edited by JTquint; 12-02-2021 at 06:37 AM.
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I think we are talking about different items. The one I replaced was the relay (fuse), you just need to cross match the numbers and amperage on the side of the relay you have installed now. It's located on the starboard side just below the flywheel in a covered fuse block. I didn't replace any of the drivers and never got an error code that I know of, as I didn't hook it up. But once I replaced the relay I no longer had any problems with surging or hard to start. Hope this helps.
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