Twin 200hp HPDI RPM Issues

[astrobud311]

I have twin 2004 200 HP HPDI's with about 400 hours on each motor. I have the digital yamaha gauges, when I bought the boat about a month ago there was a significant RPM split between the two motors. Port was WOT at 4300, and the stbd would only get about 3400, however the boat does not pull to the stbd side like the port is working more than the stbd. Both engines sound like they are reving the same. When I went out on saturday I happened to take a pretty big swell and shortly after I relized that the RPM's were matching on both motors and I was going about 4-5 knots faster than I was going at the same throttle position. Well later on in the day while running back in we hit a nice storm and took a couple big ones, after that the stbd rpm's had dropped back down to the 3400 mark and that motor seemed a little slugish to me, like I just wasn't getting the power from it that it normally has. Does anyone have any ideas what might cause this issue, I'mthinking there might be a loose connection to something but I have no idea where to even start looking.

[Tucker]

Sounds like a loose ground to me.

[astrobud311]

Really? I would think that if it was a loose ground I wouldn't be getting a reading at all if the ground was bad. What ground would you say might be loose?

[Tucker]

I'd start with the battery and work my way to the motor. My motors have about 8-ground connections on each motor. You gotta loose something.

[astrobud311]

Oh I agree something is loose, just don't think it's a ground, and considering I felt like the engine lost some performance I'm thinking it's gonna be alot more complicated. UHH I just fixed an oil issue too.

[astrobud311]

Is there anyway that something might be losing connection and dropping a cylinder??

[astrobud311]

Anyone??? I went out and checked out the motor the other day, I notice that the fuel filter assy Fuel/water sep (I'm guessing) on the side of the motor was almost empty???? It had about a half inch of fluid, I pulled the bowl and it was fuel not water. I looked at the other engine and relized that the spring inside the filter bowl was not there on the motor I was having issues with. Well I messed my hand up pretty good trying to get that filter bowl back into the housing, 2 stitches, and a cut tendon on my right hand due to a lovely metal tab sticking out from the head. Could someone please help me out before the offshore fishing season is over!!

[jb123]

if the GOOD motor only gets 4300 @ WOT i wouldnt run either of them, you need to be up @ 5500
if you plan on doing the maint, get a good manual
most likely a fuel supply issue

[astrobud311]

I'm pretty sure the low rpm's on the known good motor are because of the pitch of the prop. It's an older grady and weighs around 5 tons fully loaded, it's pitched at 19 I'm thinking maybe 17 would be the right props for this rig but I want to figure out this rpm split before I go exparimenting with props.

[Tucker]

There's tons of info here about how sensitive these HPDI's are to fuel quality. The props on my 200's are 19-pitch. Now with more of the story coming out, my money's on fuel issue.

[astrobud311]

I guess it could be a fuel issue. I just replaced the racor filters, and the fuel in the boat is fresh. Don't know what the fuel situation was with the guy who had the boat before me but I always use stabil and haven't noticed any water in any of the filters.

[astrobud311]

Anyone know what the purpose of the spring is inside the fuel filter mounted on the side of the motor, my stbd motor seems to be missing that spring and I'm wondering if that might be the problem?