Low power on a Carver diesel 355 ACMY

I would think that when you have RPM decay you would see it on Vacuum or Fuel pressure gauge if it's fuel.

I'd focus on boost and pyro next to get some numbers.

As for the erratic decay and separate fuel source, do you have room to strap down a 5 gallon tank somewhere, between motors? Put some Ts with shutoff valves right before the injection pumps and plump it into this tank. If the problem shows up, back down to idle, open valve to draw from test tank and close fuel tank valves on both motors. Just make sure your return isn't closed as it'll go back into your tank that the selector valve is switched to... Decay goes away, problem isolated. After all the time and money you've invested this would be peanuts. Maybe prove out boost and egt first. That's a good investment anyway to monitor motors.

You will find it, just a matter of time!

I'm thinking the props have a lot to do with this. If both engines act the same way it's hard to believe that you can eliminate them from the equation right off the bat. The rpm decay sounds like a fuel issue to me as well.

Tim, good luck and keep us posted! It's on'y a machine, at some point the answer will show up.

Hugo

Sounds that way, I agree but as far off as he is on making WOT rpm under load he'd have to take out many inches of pitch out of the prop - that just doesn't sound right. I had to take 1" out of my 444 with full fluids and gear but any more then 1" or 2" just doesn't sound right. Carver wouldn't prop a boat such that it needs 3" - 5" of pitch taken out to make rpm.

In theory the prop on each motor should affect that motor only but it does need to be pretty balanced across both motors. You EGT and Boost gauges will most likely tell you the whole story.

I had a bent blade on one prop once and couldn't feel anything, you would never know it. What I did notice though is my EGTs were about 75 degrees higher on stbd then port. When I pulled the props the stbd ended up having 1/2" pitch more then the port. More pitch, more load. higher EGTs...

The nice thing about the boost and EGT gauges as you will see when you're past all this is that you will get some base numbers of where your values are for your cruise and WOT. One day when something all of a sudden changes it narrows the troubleshooting process. Like if one day your port turbo is producing 10psi less boost, you will know exactly where to start digging. Without it, it becomes a shot in the dark. All mechanical diesels should have these gauges, it should be just as important as an oil pressure or temperature gauge.

Also, try removing the fuel fill cap while you are losing rpm's, it could be that you have a blocked fuel vent hose and after running for a little it's creating a vaccuum in the fuel tank and the fuel pumps aren't able to pull enough fuel.

That is correct. If you are making proper fuel pressure at the motor, then you don't have a supply issue on anything between the tanks and the motor.

Try a WOT with 1 engine in gear at a time and see what each one turns up to. Do not do this for a long period of time, only a minute or two each engine. If one turns a much lower rpm, then that is the motor I'd be looking at. I've also noticed that Cummins engines are not very torquey and if they're over-pitched they effect performance a lot more than CAT's or others that make a lot of torque.

Also try running the boat with the air filters removed and the engine room hatch open, you might also have an air restriction and the motors are not getting enough air to turn up rpm's due to either dirty/restrictive air filters or too small air intakes to the engine room.

That is also something I didn't think of. Carver had to add extra vents on the old 42 aft cabins when they put diesels in them. Correct me if I'm wrong too but on a diesel boat should the bilge blowers both be pulling air out of the bilge or should one be bringing air in and one pushing it out?

I've seen it both ways, depending on the size of the hull vent openings. Europeans like to use 1 in and 1 out, mostly from what I've seen. Americans like to blow out and allow air to naturally flow in from the intake vents. But I've seen it either way from both types of manufacturers.

Gasoline vessels, the blowes can only blow out in case the blower is making sparks.

We have a Carver 444 with Cummins 370's and have been having some of the same issues as Tim - low power/not achieving full WOT rpm. I've posted here about it earlier. We have 4 blowers in the engine room all blowing in.

Definitely know about the gas boats but I've seen it so many different ways on diesel boats.