450C 6CTA Loss of Power Troubleshooting

[Alex F]

My PORT engine (Cummins 450C 6CTA) is experiencing loss of power. It reaches only 2300-2350RPMs, while STBD side gets to 2600RPMs.

Here´s some data and symptoms:

1. The engine seems to work as expected until 2300RPMs. Starts fine, idles fine and no hiccups all the way to 2300.

2. While getting on plane I observed NO SMOKE at all.

3. During my preliminary test runs, I´ve noticed that the engine is also experiencing elevated TEPMs. It didn´t take too long for the temp to rise close to 200*. Once I saw the temp go so high I throttled back.

I´d like to think that high temps and loss of power at WOT are two separate issues. But, I also guess that if there´s a fuel starvation and the engine is working too hard, could lead to elevated temps.

4. While on plane at 2300RPMs, the Oil pressure, on the PORT engine, registered at about 80PSI, which seemed on the high side, as my STBD side was at about 60PSI. This is on analog gauges at the dash. I didn´t verify the numbers on the engine gauges.

5. The boat is always loaded and during my last run had 3/4 of fuel and full water. Environment – hot summer day, air temp in 90s and water temp in 90s.

6. Preliminary observation showed no issues with raw water flow. I´ll investigate it in great detail, but for now no difference between STBD side.

7. Aftercoolers were fully serviced less than 2 years ago.

8. It´s not “the boat”. Even though I had some growth on the running gear and my bottom wasn´t in perfect condition during the test. I lost couple knots, but there should be no reason for the PORT side perform any different than the STBD side. It was always the same before.

9. There´s no issue with running gear. I can freely spin the prop with my hands and there´s nothing wrapped on the shaft. Some growth on the running gear was the same as on the STBD side and should not prevent the engine going above 2350RPMs.

I was hoping to get some guidance in regards to pressure gauges and pressure ratings.

Can someone suggest on the following items:

1. What gauge fits my engine to test fuel pressure coming from the lift pump (low pressure side)?

2. What gauge fits to test high pressure pump side.

3. Where can I find the fuel flow ratings for the lift pump to see if the flow I have meats the specs?

4. Where can I find the fuel flow ratings for the high pressure injection pump to see if the flow I have meats the specs?

5 Could you please point me to where (connection port location) to connect those gauges (lift pump and HP pump)?

Any help is greatly appreciated.

Topic

[Tony Athens]

Penny Wise Pound Foolish

Maybe you should read thus 1st

What a Marine Diesel Turbo should look like when Inspected

[blairlavelle]

Tony Athens wrote:

Pictures, pictures and more pictures..

Water/rust/corrosion in the turbos? And you are going to install a new one with out correcting the “WHY” this happened ? You are kidding, right?

No, we’re going to install a spare used one to get the boat working.
This is a charter boat, and our country’s borders are currently closed, so our business is struggling. We cannot afford a new replacement right now.
Once we are in a position to remedy this properly, we will redesign the exhausts, and fit a new turbo.

I hate doing things this way, but needs must.

[Tony Athens]

Pictures, pictures and more pictures..

Water/rust/corrosion in the turbos? And you are going to install a new one with out correcting the “WHY” this happened ? You are kidding, right?

[blairlavelle]

Hi Tony, thanks for your reply.

I have now removed and stripped the turbo in question.
It was supplied with the automotive exhaust housing fitted, but the previous member of staff removed this, and fitted the core into the existing marine exhaust housing, despite the large build up of corrosion inside it. This corrosion was built up to the point it was fouling the exhaust wheel, and, once bolted in place, stopped the turbo from turning.

I am in the process of fixing this, but will be looking to source a replacement turbo in the near future.

Long term, I suspect the wet exhaust may need some attention, as it is a design that rises out of the turbo, and the corrosion inside the turbo suggests water is running back down into it.

[Tony Athens]

“Blairlavelle”

Let me understand this please..

Chinese turbos from a Dodge ram, , some kind of “adaptation” , and you are asking for help to sort out “exactly what” ?? We need way more that that to even attempt some type on answer to help.. Do you know how to post good pictures what what has been installed on your engines?

[Tony Athens]

Alex,

You ARE NOT following my logic at all… You are in denial.. If your vessel is traveling at a less speed than in the past as the same engine RPM, the issue is not the engine–It’s the boat…..

But you are welcome to spend time and money going about your issue your way…. Your hired techs & parts houses will appreciate it.

Tony

[Francis Valerio]

If you can not find anything that is wrong, I tend to agree with Tony to look at the bottom. Maybe you picked up some old netting or rope and it is wrapped around the shaft or prop to some degree. It does not take much to affect the performance.

Be more hyper-sensitive to vibration, can you feel possibly a dinged prop. The prop may “look” good to the naked eye if it got whacked and is way off though. Just a few thoughts…

[blairlavelle]

blairlavelle wrote:

I’m having a similar issue.

I have a pair of 380’s in a 55′ Bayliner.

Both engines pull well and smoothly up to 1500rpm, where the starboard simply stops revving under load. No smoke at all, temp starts to creep up, and no amount of throttle will raise revs.

These motors are a little underpowered for this big old boat, so without both operating well she will not get onto the plane, and sits at 10kts, with black smoke pouring out the port motor as it cannot accelerate the boat any further on it’s own.

One mechanic thinks the injection pump needs rebuilding, another says it turbo (it’s new, and there’s no smoke, so not that!), another says cooling system.

Interested to see if we have a similar problem, and any advice on a fix would be greatly appreciated!

So, to update: firstly, I made a couple errors. These motors are 370hp 6BTAs!
Secondly, we found the problem. a year ago, the previous manager replaced the turbos on both engines with $300 chinese units for a Dodge Ram. To make them fit, he bolted them into the marine exhaust housing, not realising the exhaust wheel of the port turbo was fouling. So it has been producing zero boost, and the stalled impeller wheel has been acting as a restrictor. This means the anueroid has had a constant vacuum to it, meaning no extra fuel at 1200-1500rpm.

We hadn’t even considered the turbo as it was new, and a failing turbo will usually lead to excess smoke. I’ve never actually seen a seized turbo before!

[blairlavelle]

Similar issue with pair 380 6CTA

I’m having a similar issue.
I have a pair of 380’s in a 55′ Bayliner.

Both engines pull well and smoothly up to 1500rpm, where the starboard simply stops revving under load. No smoke at all, temp starts to creep up, and no amount of throttle will raise revs.

These motors are a little underpowered for this big old boat, so without both operating well she will not get onto the plane, and sits at 10kts, with black smoke pouring out the port motor as it cannot accelerate the boat any further on it’s own.

One mechanic thinks the injection pump needs rebuilding, another says it turbo (it’s new, and there’s no smoke, so not that!), another says cooling system.

Interested to see if we have a similar problem, and any advice on a fix would be greatly appreciated!

[Alex F]

I follow your logic, Tony. But my bottom was in decent condition and even though the running gear was due for cleaning, I’ve ran in this shape before and had no issue.

I’m having a concern that it could be some sort of a fuel restriction (either supply to the engine or on the engine side) for the following reason. Since both side had the same amount of growth generating extra drag, why would STBD perform as expected and get to 2600+RPMs. I dove under the boat, shortly after the test run and didn’t see any difference between the running gear growth. I spun each prop freely by hand. There was also nothing on any prop/shaft that could lead to extra drag on the PORT side.

I understand that in order to get closer to the valid conclusion, I need to check few things and produce more detailed data. I’ll report back as soon as I have something.

Quick question, which pressure tester would you recommend I use and where do I connect it in order to validate fuel flow to the HP pump? Maybe you have a link to an article, with pictures, you posted some time ago?

[Tony Athens]

Need to compare 2300 now vs. 2300 before ……..On the surface it does not sound like an engine issue–It’s sounds like you need to pull the boat and have the engine bottom & running gear cleaned properly……….The excess or added drag is putting your “hand to plane” boat over the edge as to getting it up on top on a clean plane

[Alex F]

My boat is not efficient in the 2200-2300 range, so I avoid it. My normal cruise on plane is at 2350-2400RPMs.

As per my older record, very light wind behind me and .25kts current, 1/4 of fuel, 20-21kts @2300RPMs.

I don’t have exact numbers from my last run on 2200. If my memory serves me right I was at around 15-16kts at 2300, but I’ll have to do another run to verify that.

Since my bottom/running gear was close to the time of being serviced, I was expecting to loose couple knots.

[Tony Athens]

2200 RPM or 2300 RPM = what vessel speed before ?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

2200 RPM or 2300 RPM at your last run = what vessel speed ?

[Alex F]

Tony Athens wrote:

Exactly when did this Lower RPM occur? Last run or?

What the history of the past RPM vs. vessel speed?

Hi Tony,

Thanks for your reply.

I’ve owned the boat for the past 10 years. It never had an issue operating to the specs (both engines). Shortly after the purchase, I tuned the props to be in 2650-2680 range, so I can keep my engines happy.

Yes, the issue was observed during the last run. In the past couple months, due to covid, we did only short trips to a local anchorage and those were done running at low speed (my usual trawling speed is 8.5-9kts @1300 RPMs).

Even though I do WOT test on rare occasion, I usually advance throttles gradually to about 2500RPMs to get out of the hole and then settle her at around 2350-2400RPMs for normal cruise speed. Since my boat is super loaded with lots of stuff, heavy tender on a hydraulic lift and I usually have good load of fuel and water, I’m cruising in the range of 19-20kts. With freshly painted bottom and light fuel load she tops out 27kts at 2650RPMs.

During my last test run, when I observed the issue, my bottom was not ideal (a bit of slime, but not too much and few barnacles sprinkled around), and running gear had some growth. I have a diver doing routine bottom cleaning, so this was about 2-3 weeks after the bottom was serviced last. I wasn’t expecting to break any speed records, but just wanted to put her under normal load, exercise the turbos and clean blow by. If my memory serves me right, with PORT side just over 2300 and STBD at 2400RPMs she could only do in the range of 16.5-17kts. When I saw the PORT side struggling to go past 2300 I decided to do a WOT test on both sides. But, as soon as I saw the temp climbing up on the PORT side, I throttled back to avoid harming the engine.

Summary of the last test run:
PORT side:
1. Max RPMs observed was around 2350. Advancing the throttle forward (there was more room to go) didn’t increase RPMs.
2. Water temp was rising to unacceptable level. When it got close to 200 degrees, I pulled the throttles back.
3. Oil pressure registered at around 80PSI at 2300RPMs.

STBD side:
1. Don’t recall exactly how much above, but it definitely hit 2600RPMs.
2. Water temp remained in normal range 180-185 degrees.
3. Oil pressure was at 60PSI, which is where it always was at 2400RPMs.

I do all my regular maintenance, so I highly doubt that there’s a fuel restriction at the filters level. The fuel side (all filters) were changed in spring. I do it annually and as per my observation, the racors were in pretty good shape.

Plan of Action:
I’ll be treating loss of RPMs and high water temp as two separate issues.

On water side
1. I’ll double check the intake flow. I have screens on the bottom covering the scoop strainers, so I’ll double check that there’s no restriction in the flow and will compare it to the STBD side.
2. I plan on doing a quick test to see at what point the temp starts rising. I’ll run it at different ranges 1500, 2000 and finally 2300RPMs.
3. I doubt it’s an issue on the impeller side, b/c I replace mine annually and it’s just approaching the time to replace them. They always look like new when I take the old ones out. But, if all checks out before the impeller pump, I’ll replace the impeller as the next logical step.
4. Finally, if no improvement, I plan on descaling the system by running barnacle buster through it.

On Loss of Power side
1. I’ll do no load WOT test and expect to see 2920-3020RPMS.
2. I’ll check the throttle linkage to make sure it’s not something simple as loosened or stretched cable or something else preventing for lever to move the rack to WOT position.
3. I’ll replace the racor and the secondary filter on the PORT side, just to get this simple stuff checked off, but I’m not expecting it to solve the fuel restriction problem (assuming that’s what this is).
4. Using an air compressor, I’ll blow the fuel feed line from the racor to the tank. I’m thinking that if there’s any sludge it’ll clear any potential blockage in the hose or the tank tube.
5. If all above doesn’t solve it, I’ll have to shift my focus on the engine components. At this point I was thinking to use fuel pressure gauges to check if the fuel flow is to the specs. I was hoping to get some help on what fuel tester I need to get and where to connect it.

Please let me know your thoughts.

[Tony Athens]

Exactly when did this Lower RPM occur? Last run or?

What the history of the past RPM vs. vessel speed?

[Author]

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