Lost 200 RPM on Starboard 200 HPDI

[jrgcpa01]

Out of the blue my Starboard motor dropped 200 RPM pretty much all the way from idle to WOT. It will hold RPMs and I can synch with the port motor by giving it more throttle.

The motor has 350 hours and seems to run good, idles fine, and does not exhibit the symptoms of dirty mystery filters in the high pressure pump.

It just runs 200 RPM less than the port motor and it will not reach the 5200 RPMs that it used to. The port motor still hits 5200 at WOT.

I changed plugs and it ran great for about a mile or two, then it dropped down 200 RPMs below the port motor.

I notice that it smokes some at start up, while the port motor remains smokeless.

I am thinking low pressure fuel pump problems.

Any ideas are greatly appreciated.

Thanks

[boats.net]

Check throttle cable adjustments to see if both engines are going to full throttle.

[jrgcpa01]

Thanks for the reply.

My gut tells me that it is not the throttle cable, primarily because of the smoking at startup and also the intermittent nature of the rpm drop when it first occurred.

I did not mention in my first post that when I first noticed the rpm drop, it would vary some. At times the motor would reach full and equal RPMs with the port motor and then drop back to being 200 RPMs less than the port motor. Eventually, it seems to have settled into always running at less RPMs than the port-side motor.

I have ordered new fuel pumps and will install them. Even if the problem is not being caused by damaged pumps, at 300+hours, it is probably time to replace them anyway.

Any other thoughts or ideas are appreciated.

[jrgcpa01]

Replaced the two fuel filters and put in new set of plugs. (Noticed that two of the plugs were noticeably oilier and grimier than the other 4)

The motor seemed to run fine for about five minutes and I anchored up for a while.

Let boat sit for about 30 minutes and the problem returned, but now I seem to be losing 300-400 RPM's on the starboard motor versus the port motor. Max RPMs are now 4800 or so...was 5200.

I do not get the classic bogging down when giving it throttle, that typically happens when the filters in the high pressure pump are clogged or dirty.

I have never messed with the fuel injectors, but am now wondering what else could be going wrong. I guess I will clean all of the other filters again (VST, medium and high pressure). If the problem remains, I guess its time to pay the shop an expensive visit.

[rodbolt17]

find a dealership that employs at least 1 master tech.
HPDI has some unique issues.
you can use the yamaha marine dealer locator function to find a dealership in your area with a master tech.

[jrgcpa01]

Thanks Rodbolt,

Sadly, located on the coast south of Tallahassee Florida, there is not a Master Tech within 100 miles (closest in Dothan, Ala).

I learned many years ago how the local repair guys operate and have been forced to self-repair in almost all cases. Fortunately the only real problem I have had with these motors have been the basket filters in the high pressure pumps. Once I figured that out, and added 2 micron water separator filters to go along with the 10 micron filters, I have operated for 3 or 4 years with no problems.

This one has me stumped. I thought sure that it was the fuel pumps, given the fact that I get smoke at start up with this motor but not the other one.

Thanks again.

[99yam40]

Computer should show if HP pump is putting out proper pressure before and after RPM drop, and monitoring low fuel pressure at same time should show if those pumps or other filters have a problem.

I have read before that Rodbolt is not a fan of those 2 micron pre filters

Maybe a good Idea to have injectors sent of and cleaned/tested

[jrgcpa01]

Go ahead and call me an idiot, but I just can not force myself to patronize the local Yamaha repair shop that does not employ a Master tech as recommended by Rodbolt.

Based upon past dealings with them, I know I am faced with a minimum $800 repair bill so I decided to take that $800 and buy me some new toys and see if I can't mess things up really good!

Earlier today I went online and ordered the following:

Version 1.33 of the Yamaha YDS diagnostic software
A Fuel Pressure tester
A Compression Tester
A Leak-Down Tester
A spark tester
A remote starter
A fancy electronic multi-meter

I already have a bunch of the high pressure pump basket filters and have just replaced the low pressure fuel pumps and spark plugs, and I am about to order the $80 medium pressure Canister filter with the special hose clamps and the $25 VST replacement O-ring.

Even with all of the above I still have over $300 left to spend...what am I missing?

Hey, at least I'll have some fancy tools to loan to my neighbors!!

[99yam40]

I just hope the meter will read the peak voltages like Yamaha says

[jrgcpa01]

Turned out to be two injectors that would stick open after getting hot causing no.4 and 6 cylinders to flood. Pulled injectors and sent them off to Flagship for cleaning. Runs great now.

[jrgcpa01]

find a dealership that employs at least 1 master tech.
HPDI has some unique issues.
you can use the yamaha marine dealer locator function to find a dealership in your area with a master tech.

Just curious. What would those "unique" issues be?