Any Yamaha HPDI experts out there? still bogging down

[BTF112989]

hey everybody!
My 2001 Yamaha 150 HPDI bogs down while at speed or while getting up on plane. It drops down about 300-400 rpms for about a quarter of a second, then goes back to normal operation. It does this sporadically. I recently replaced EVERY filter in the entire engine. I replaced my external water fuel separating filter with a 10 micron Racor filter, changed out the water fuel separating filter in the engine, changed out the VST screen filter on the bottom of the fuel pump, changed out the medium pressure fuel filter, and replaced both micro basket filters inside the high pressure fuel pump. My battery cables are 2 gauge cables that are 18 feet long, so I don't think there is a voltage drop. They are also only 8 months old & my batteries are only 8 months old. The connections are all clean & tight.

Does anyone have any other ideas of things to check for that could be causing this?

Sometimes it takes about 2 or 3 cranks to start the engine, so I was thinking that it could be the lower pressure fuel pump diaphragms. The fuel bulb is hard sometimes and not hard other times.  The engine has 350 hours on it & was put into service in 2006.

I put the engine on a new boat this past December, and it ran great all the way up to 5500 rpms. Now on the same boat, it will only hit around 4600 rpms.

I'm not sure if my last 2 comments are related to the problem or not, but I thought I would add them anyway.

Could the low pressure pumps be causing my low WOT rpms & the sporadic bogging down?

I posted this question on THT & iboats, but I trust everybody on this board a whole lot more.

Thanks,
Ben

[Blue Agave]

Have you changed the anti-syphon valve on the pickup on the tank?

[Aswaff400]

sometimes there is a screen on the pic up in the tank, could be clogged, we had that problem on our sea ray with both motors...

[BTF112989]

No to both questions.  Do I just disconnect the pickup on the tank & lift it out to find the anti-syphon valve & screen on the end?  I would hope that these aren't the problem as the entire tank was replaced in 2008.  

Maybe I need to try running the engine on a remote gas tank.

Thanks!

-Ben

[flounderpounder225]

Ben
I have crawled around my 250 HPDI quite a bit, I would definitely try the remote tank option as eliminating the installed fuel cell as a problem.  After that has been tried, if she is still failing, there is the possibility of the micro basket filters that are installed in the injectors, (mine have been removed) and then there is the fuel pressure issue which you eluded to, and.. the only way to truly check that is with a laptop with the Yami Program, I don't think there are shrader valves to hook to, plus the HP side is beyond most gauges you will find.  Do the remote, and lets see what happens..

[gran398]

Ben, jdupree had a similar issue with his 200. You may want to search his posts from awhile back regarding this. He did some sleuthing on THT, received good advice, and fixed it immediately.

[jdupree]

Zero in on your LP pumps.  Unscrew each one from the block and while holding it with your fingers behind it pump the bulb.  See if you can feel gas back there.  If so, that might be your problem.  When did you last replace the LP pumps?

[saltfly]

I have to write this down in my book. I have a 150 HPDI that only has about 60 hours on it. So I may run into this problem down the road. I’ve found keeping notes on problems and repairs for them, in my repair manual helps.

[BTF112989]

Thanks for all of the replies!  I am driving to the lake this afternoon & I will try everything recommended.  I think I will run the test jdupree told me about on the LP pumps first, then run the engine on a remote tank.

I found a post on THT by Andy from SIM Yamaha that seemed to describe my problem exactly.  Here is what he said about the low pressure fuel pumps:

"All Yamaha 2-strokes have low pressure fuel pump(s). Your engine (Pasta) has two of them adjacent to the engine mounted oil tank. Follow the fuel hose coming out of the engine mounted fuel filter.Those LP pumps suckthe fuel from the boats tank and deliver the fuel to the VST. That is the location for the med pressure fuel pump. From there the fuel is pumped under 50psi to the HPDI belt driven pumps on top of the engine. On your Z300 there is two HPDI pumps. These pumps squeeze the fuel to 1000 psi plus or minus and send it off to the injectors.

The achilles heal on these LP pumps are the internal diaphrams. With the ever changing fuel types, it is common forthe diaphrams tofail and leave the pump not being able to pump an adequate amount of fuel. When they do fail, fuel tends to leak right into the powerhead thru the vac pulse port on the back of the pumps. You can check the diaphrams by testing them with a vac tester, or the easier way is to remove the pumps with the fuel hoses attached. Then pump the primer bulb hard. A good pump will hold that pressure. A bad pump will leak fuel out the pulse port. .............and its pretty obvious when it does.

If the LPfuel pump is bad, a common symptom is under load surging, hard cold starting and excessive smoke on cold start. A HPDI engine might blow a bit of blue smoke for a second or two on cold start. Anything longer then that, you should start to look into why.

2-stroke Yamaha owners should replace those pumps on a 2-3 year preventative schedule. They are not expensive and are easy to replace.

Andy"

My engine blows excessive amounts of blue smoke for 12-15 seconds on a cold start up, has the under load surging, and hard starting.

Jdupree,
I will perform that test tonight & see if the low pressure pumps are my problem.  I'm betting thats what it is.  My pumps have never been replaced, so I'm sure that I'm well overdue.  My engine has 354 hours on it right now & has been in service for 6 years.

Saltfly,
That is a great thing to do because these engines seem to require the very very clean fuel & can be frustrating before you learn all of their weakspots.  I'm still learning!  Preventative maintenance is the key with these engines. Make sure you have an external water fuel separating filter to save you from changing the filters in the engine as much as I have.  The medium pressure fuel filter at $75 a pop isn't a fun one to replace frequently.

-Ben

[flounderpounder225]

JD,
So same LP Pumps on the HPDIs as The OX-66's?

[jdupree]

JD,
So same LP Pumps on the HPDIs as The OX-66's?

Not quite sure Marc   One thing I have learned from reading up on Yamaha's and from personal experience is that these LP pumps need attention every 2 to 3 years.

I was having his same symptoms when my LP pumps went bad. Both of them were leaking from behind.  Motor was "stumbling" at low rpms and did not idle very well.  Even if they are a little different, I would think they would display close to the same symptoms.

I have been wrong before, but I would bet heavy on the LP pumps.

[BTF112989]

I just called my dealer to see if they had any low pressure pumps in stock.  He said that he was pretty sure the ones for my 150 hpdi fit any V6 Yamaha.  It says at the top of the page on SIM's website that the part number is for a 2006 250hp hpdi also, so I'm pretty sure they fit all of the V6's.  

I'll go pick two up tomorrow morning & throw them on to see if that fixes my problem.

Thanks,
Ben

[jdupree]

Still perform that test when you can.  Hate to see you by LP pumps if you don't need them.  If the diaphrams are bad when you pump your bulb you will feel the gas leaking behind the pump.  Just loosten it or remove it in order to get your fingers behind it.

[BTF112989]

I just changed out both low pressure fuel pumps on my yamaha. One diaphragm was cracked in 3 places. The other was cracked in 4 places. I now have a smoother idle, a lot less smoke on startup, and gained 200 rpms on wot. However, I still have a sporadic 200-300 rpm bog down for about a quarter of a second, then everything is normal again. I'm running it around today to see if the problem persists. I'm going to try a remote gas tank tomorrow. Any other suggestions until then?

Thanks,
Ben

[dburr]

  Motor was "stumbling" at low rpms and did not idle very well.  Even if they are a little different, I would think they would display close to the same symptoms.

I have been wrong before, but I would bet heavy on the LP pumps.

John could you please define"stumble" ?

My OX66 150 starts after an few day sit with a 1-2-3 crank then idles fine.  On the idle off the dock there is a little smoke.. Then she runs fine at speed, when I slow down to idle sight seeing or trolling for any real length of time, she may sneeze (sounds just like a little old lady church sneeze) a bit of exhaust, and die but will start right back up, or sneeze and keep idling..  No real consistancy at this point.  WOT is 4900, but the wheel has a ding on one blade.  PO said the boat would do 43 at WOT, full fuel with 3 big guys.  With just me and a half tank I see 37 (which I was attributing to the ding)..

This sound like sick LP pumps?

Thanks!