Low power on a Carver diesel 355 ACMY

I’ve been trying to troubleshoot a low power problem with my ’98 Carver 355 ACMY powered by twin Cummins diesels. I’m not able to get rated WOT rpm which is suppose to be 2950 rpm and I've done just about everything with the engines to rectify this. I’m now focusing on the props.

I would like to hear from anyone who has a diesel powered 355/356 and find out what your WOT rpm is and what props you have. As a reference my props are 23X 26 and were reduced from 23 X 27 after I purchased the boat.

Tim

Thanks guys. The engines are Cummins 330 6B TA M3's which I believe is the only diesel engine carver put in these boats.

To answer Marmots questions:

Is rpm confirmed by independent tachometer? At survey 2 years ago the tach's were +- 50 rpm. I was getting 2700 rpm at that time.

IS bottom clean? On a regular basis. Last was mid December

Are air filters clean? I replaced the airsep CCV system with Seaboard Marine's envirovent system which included new air filters. That was also 2 years ago. I haven't cleaned them in the 250 hrs they've been on the boat, but after the install I was getting 2700 rpm.

Is air getting to engine room? I'm not sure how to measure air flow to the engine room but when the blowers are on they suck all the air conditioning out of the boat. The blowers are on when the engines are on.

Are engines smoking under load? Not much, but do produce white smoke when first started and does disparate but not completely disappear at rpm.

What rpm can you obtain? 2700 on both engines. Almost exactly and exactly the same on both engines leading me to believe the low power is external to the engines. ie props

Another dozen or so questions await ...

Other information:
A fuel pressure gauge on the port pump confirms good fuel pressure to the engine. 30-35 psi at 2000 rpm.

Both after coolers have been properly serviced and have 3 hours on them.
They were previously serviced when I bought the boat.

Both exhaust sides of the turbos have been checked, no corrosion noted.

Thanks guys. Actually I've had two problems with power and at first I thought they were related. The first problem was a decay in power problem that I thought was caused by "bad" fuel when I bought the boat. However since purchase, I've run several tanks of fuel through the engines and the tanks have been cleaned twice. Vacuum gauges seem to confirm the contaminated fuel issue but the filters were always clean. I changed them anyway until Tony Athens on boatdiesel.com after seeing pictures of the filters told me to quit wasting my money on filters, they were not the problem. But I still had high vacuum readings. I installed a diagnostic fuel pressure gauge on the port engine and have been monitoring it for the last couple of hours. So far I've had good fuel pressure which would eliminate a fuel contamination issue causing a lack of fuel to the engines. Fuel vents are all OK, they've been checked. I have not had a rpm decay issue since I installed the fuel pressure gauge, but will be monitoring this closely, along with the vacuum gauge.

Last summer on my way over to the Bahamas the starboard engine started to decay from my normal cruise rpm of 2300. I shut down the engine, changed the racor filter and switched tanks from the aux tank to the right main tank. The engine started right up and I went back to 2300 rpm. 20 minutes later the same thing happen to the port engine however this time I did not change the filter but changed the feed from the aux to the left main tank. The engine powered right back up to 2300 rpm. However this same decay issue has happened when I was feeding from the main tanks and happened later on this same trip. This was all last summer. We were out a couple of weeks ago feeding from the aux tank that was about half full and had no decay issues at all. The decay issue is very frustrating because as you can see it is inconsistent.

The second problem is the engines not reaching rated WOT rpm. I've gotten 2700 rpm the last few hours or so at WOT. I've done all the checks Tony Athens has recommended on his web site and nothing seems to be at fault.
I get 3200 rpm WOT in neutral.
I've never noticed any black smoke, just gray that disapates but never goes completely away after the engine warms up.
It's possible I'm over loaded but won't really know until I hear from someone else who has data on this particular Carver. The prop calculator on boatdiesel.com recommends 23x26 props and that is what I have at a displacement of 24000 lbs. We were out the other day with 200 gallons of fuel and 45 gallons of water. An inflatable dinghy on the swim platform and unusual for us, only a couple of cans of beer along with the normal assortment of stuff. Boat powers up easily to 2700 rpm then no more. Plenty of fuel pressure and right now about 3" of vacuum.

How would I determine that?

Ok I'll look into that. It's just seems this issue is external to the engines because both the engines are behaving the exact same way.
Bottom is clean, running gear is clean. The only other thing left is prop pitch.

Good question. From what I can remember at survey with the 27" props I got 2700 rpm the same as I'm getting now with the 26" pitch props.

Since I believe I'm dealing with two separate unrelated issues
1. Low power
2. Inconsistent rpm decay

I think I will leave the fuel pressure gauge attached to the engine (it's currently attached to an out plug on the secondary fuel filter head) and monitor it when I get rpm decay. If I get decay and the pressure is low, I know fuel is not getting to the engine in sufficient pressure or volume. Incidently, last weekend I got from 25 to 35 psi fuel pressure at rpm's from 1000 to 2500. Much higher than Tony said was the minimum. But again as I mentioned the rpm decay is an inconsistent problem. It will be monitored.

Perhaps installing an EGT gauge will give me a heads up if the engines are overloaded.