01 yamaha 150 HPDI fuel issue

[Cdnpokerface]

I have a 27 foot Sportcraft with twin 01 Yamaha 150 hpdi's. Each engine has 202 hours and I've owned them for half of that. This past weekend while using the boat I was cruising and each engine was running at approx 4500 rpm. Suddenly my poet engine dropped about 1000 rpm and then surged 2-300 rpm before ultimately limiting itself around 1500 I turned engine off restarted and tried again it worked well for approx 3-4 mins and then started the same thing and the engine occasionally bucked. The following day I took the boat out with my fuel pressure gauge attached to the vst and while trying to load up the engine the pressure stayed consistent at 50 psi. After connecting yds up I noticed that there's a code 26 set at the 202 hour mark. I then ran an injector test and all six functioned. After speaking to a fellow member who said he had similar issue I swapped the injector driver assembly with no change. Today I went back to the boat with my laptop to try again this time while trying to load up the engine I noticed the fuel pressure field went red and the value dropped to 500 instead of being in the 725 range, this is when the bucking started and eventually a stall. The engine also is stalling out under idle conditions when driving out of the harbour. Ive read a lot about mystery filters but I'm unsure if the low fuel pressure readings I'm seeing are measured before or after those filters... Any thoughts or suggestions would be greatly appreciated... I'd love the chance to talk one on one with a Yamaha hpdi guru if anyone has a suggestion on that. There are not a lot of hpdi's in my neck of the woods so I'm sorta on my own.

I was referred by another forum to find rodbolt17... so hoping he has some input on this situation... I have also replace the MP filter and still no change and engine stalls a little more under idle conditions... I have mystery filters on the way just in case.

[boscoe99]

There is no mystery to the vast majority of folks that need to know about the presence of filters being in the high pressure pump(s). Not sure how the term "mystery filters" arose. I suppose that anything that is not known is a mystery to the unknowing.

The pressure transducer is downstream of the filters within the HP pump. A clogged filter will result in the loss of fuel pressure downstream from the filter. Same as with any other filter.

Swap pumps from one motor to the other to see if the problem moves with the pump as a test if you want. Or, simply install the new filters and see if there is an improvement in fuel pressure.

[rodbolt17]

I don't mess with them.
I send the pumps to Flagship marine in Punta Gorda FL.
they rebuild, clean and test them for leaks before shipping it back.
call them and talk to Jeff.
sounds like you have debris in the HP pump.
keep dogging it and you will get to post about detonated pistons due to lean running.

[Cdnpokerface]

thanks very much for the input guys.

[99yam40]

glad to see you found some answers from experienced people.
hope it leads you to a fix very soon

[rodbolt17]

the reason I don't mess with them is two fold.
one I have no way of testing the repair other than running it.
two is in todays litigious society a fuel leak at 725 PSI would most likely NOT be a good thing.
IF I do it and something catches fire I am on the hook.
IF YOU do it and it catches fire all I can say is I tole ya .

Flagship has the tools and trained folks to properly disassemble,clean/repair and TEST after the repairs.