Calling All Yamaha HPDI Experts! 150 HPDI bogging down, but not filters!

[BTF112989]

Hello everybody,
I have a 2001 Yamaha 150 HPDI that 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.

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.

Thanks,
Ben

 

[jerome4506]

Re: Calling All Yamaha HPDI Experts! 150 HPDI bogging down, but not filters!

I have replaced the low presser fuel pumps on my 150 hpdi , I may have got to them early. My simptom was a slite slik of fuel on the water at sea. A way to test is to unbolt the pumps and pump full with bolb. One of mine leaked from the back and the other didn't . I was told that this can happen even on a good pump. Decided to put 2 new pumps in an now have now fuel leak so was low presser pumps.

 

[BTF112989]

Re: Calling All Yamaha HPDI Experts! 150 HPDI bogging down, but not filters!

I don't have any evidence of fuel leaking into the water, but I will run that test on my low pressure pumps. I may just change them out to see if that will fix the hard start issue.

The bogging down is just driving crazy because I've been chasing this problem all Summer.

Thanks,
Ben

 

[jerome4506]

Re: Calling All Yamaha HPDI Experts! 150 HPDI bogging down, but not filters!

let us know if you solve the problem. cheers.

 

[BTF112989]

Re: Calling All Yamaha HPDI Experts! 150 HPDI bogging down, but not filters!

Here's an update, but I am still having some problems.

I 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. So I ran the boat from Saturday until Tuesday, and I thought my issue was all cleared up. After I changed the LP pumps, it bogged down a few times right after the fuel pump change, but everything got better. The engine ran great the rest of Saturday until Tuesday with probably 5 hours of run time during those days. I took it for a little 45 minute cruise before I put it back on the trailer yesterday. During that cruise it bogged down 3 times. They weren't violent, but noticeable & enough to make me lose confidence in the engine again. So the problem seems to be coming back.

I did notice a few drops of gas leaking out of a fitting on the inlet into my high pressure pump. The leak is right at the fitting where the fuel line exiting the medium pressure fuel filter meets the fuel rail & the high pressure pump. It only leaked about 3 drops on a 45 minute cruise, so its not squirting out by any means. I need to check the o-ring in there when I go out next.


View attachment yamahahpdifuelleak.pdf

The fuel barely drips out of the top of part #12, which makes me believe the o-ring(part # 13) has broken.

What I'm not understanding is that it ran great for several days not missing a beat(even with the few drops of gas leaking), then just as I'm about to put it back on the trailer...it reverts back to its old ways.

I also have thought that it may be fouled plugs or a bad/clogged injector. I need to check into that.

I may just buy new plugs even though these only have 60 hours on them.

I saw somewhere that people are able to cycle the solenoid on their injectors with a 9v battery to make sure they are working. Anyone have any idea how to do this?

Does anyone else have any new ideas?

Thanks a bunch,
Ben

 

[Capt Ken]

Re: Calling All Yamaha HPDI Experts! 150 HPDI bogging down, but not filters!

What is your fuel pressure on the HP pump?

 

[yamatech43]

Re: Calling All Yamaha HPDI Experts! 150 HPDI bogging down, but not filters!

Really, get a fuel pressure gauge(cheap) and hook it up to the schrader valve, this will let the diagnostics move forward.