300 hpdi mystery

[COJones]

Ok Guys,
This takes the cake. I have a twin 300 HPDI rig with my port motor doing the lost rpm suffle. That is, I plane out with both motors syc'ed up to lets say 3200 rpms, in 15 to 20 secs after everything stabilizes my port motor will drop, 200 rpms and about 1 to 2 minutes later it slowly comes back to syc. With that said, I have monitored both medium pressure and HP during this event (ie medium press 50 psi, HP 986 psi). Additionally, all variables monitored using YDS (ie TPS, Spark, Fuel PW, temps, etc..) remain constant except for of coarse the fuel PW; it goes up ever so slightly with the rpm drop (that is expected given the load appears to be increasing for no reason). This has been happening for about 2 yrs and now and I have finally decided to fix it but I'm at a lost. One more detail, the motor will not achive max rpm, hence the concern.

Somethings I've done: swapped entire VST assembly with good motor (no change), swapped HP pump with good motor (no change), swapped entire coil and spark plug wire assem with good motor (no change)....any ideas anyone? Oh, and good motor remains running good. Compression is good and even, no codes. Any help appreciated. I even swapped fuel line just incase and still no change.

[BastiaanMBok]

200 rpms?? did you interchance ecu? or maybe the port side engine oilinjectionpump richer then the starboard side? or portside (counterrotating left hand ) has bit more lag on it because of extra gears).
is your boat well balanced,like not leaning bit to one side?
could be any little thing.
cheers
BMB

[COJones]

I have not swapped the ecu. When this occurs, the motor drops out of sync so you can hear it. The strange part is that this rpm drop (it could be more than 200 at times) happens slowly roughly 15 secs after the boat is on plane and sync up. It's like everything is perfect and all of a sudden you realize the engines are losing sync.

[Sequoiha]

do you have the yamaha fuel management sensors installed on the boat, I had a similar issue with a 31 cape horn with twin Z300's, after extensive diagnostics, even with the Yamaha DSR for most of it, we found the top of the sensor was sucking air, it wasnt much, but it was enough to cause an issue, just a thought. also have you replaced the high pressure filter just above the VST.

[COJones]

Yes, I do have the fuel management system but I swapped fuel lines (with the good engine) after all the filters and flow sensors. The good engine continues to run good and the bad no change. I do appreciative the thought and that kinda of experience is what I'm looking for. If I don't find anything else, I might just go after the injectors.

Yes, the filter after the vst was replaced and when I swapped the vst with the good engine I swapped it at that filter so a known good assembly was the swap.

[rodbolt17]

will either engine turn at 5500?
did they ever turn 5500?
overpropping will cause that issue.
fuel rail pressure should be closer to 1100 PSI.
possible the pump filter is clogging.
can you post a printout at the failure RPM and load?

[COJones]

Thank you Rodbolt!
Before this started happening the boat would consitently product 57 mph @ 5700 rpms on both engines. The fuel pressure readings are consitent between both engines. I have been posting information on all 3 forums ie Hulltruth ( 2004 300 HPDI Mystery - The Hull Truth - Boating and Fishing Forum ), Iboats, and this forum. Attached is an example of what I'm seeing. Any next steps or experience would be very welcomed.

[99yam40]

Sounds like this has been happening for quite some time now(couple of years).

When was the last time these motors ran at 5700?
Sounds like they will not do it anymore from what I have read, but you have not said what the WOT RPMs are now.

Where did you get the replacement lower unit from?
And are you positive the gear ratio is correct?

[COJones]

WOT was 5700 fully trimmed and I believe that is still the case if both engines ran the same. I have not attempted WOT because I'm afraid of blowing the port engine. From very limited WOT runs that i have made the starboard engine pulls over the port by around 400 rpms e.g.port 5000, Stb 5400.

The replacement LU was purchased new from a local Yamaha dealer, same part number as.what I took out.

Thanks for your thoughts, everything stimulates new ideas.

[99yam40]

can you show a print out with all of parameters instead of the chart showing just a few?

The gear ratio was just a thought as Rodbolt17 said over propped can cause something like this, and you said this started about the time you replaced lower unit

Rodbolt did say HP was a little low

[COJones]

Attached is one of the runs with all pids. I changed the file extention to upload but it is a CSV same as text. Thank you for looking at this. I think I might go after the injector basket filters. Any ideas appreciated.

[99yam40]

all of those numbers make my eyes hurt

I do not claim to know anything about these read outs, but did notice a small fluctuation in fuel pressure and pulse width along with RPM

Hopefully Rodbolt17 will chime in again with his thoughts

[rodbolt17]

double check your intake air and MAP readings.
also carefully check the lift pumps for leakage.

[COJones]

I can do that, I actually ran about 3 to 4 times sampling data; wish it would sample alittle faster. The lift pumps where replaced about a month ago and the ones I took out where not leaking.

Are there basket filters in the injectors? If so I might go after that very soon.

[COJones]

Since the only things I'm not able to verify with out replacement are the injectors (given the open loop control); even though the symptoms aren't indicative of an injector issue. Can I hear some success storys on cleaning and or replacing injectors? Has anyone had good results with professional ultrasonic cleaning services? If weather permits, I'm pulling those guys out tonight. Any feedback would be welcomed.