Bayliner 3788 Low rpm

[yoeman]

Looking for some help to start trouble shooting
1997 Bayliner 3788
250 6bta
650 hour engines
Bottom is clean
New filters in the last 50 hours
After coolers serviced
I have no history on props but believe they are factory
The boat will not plan out and only pulls 2200 wot
14 knots top speed with 3/4 fuel not loaded
Black soot and smoke for about the first 5 minutes then it cleans up but still not getting rpm
Runs smooth and has clean airseps
Any thoughts on this would be a big help
It may be over proper or are the 3788 just under powered with the 250hp

 

[CPseudonym]

That boat should be close to a 20ish knot boat with 500 HP

Not qualified to speculate the cause

 

[yoeman]

I'm going to look further into why it's not performing
I would love it if it would plan out
Any ideas would be great
Thanks

 

[Capt. Jon]

While at the dock and in neutral can the engines reach their no load wot rpm on the data plate? If so is there information available with factory data on what props were supplied and then compare to what you have on board? At least a place to start.

 

[yoeman]

The boat is rated to 2600 rpm and it will pull that in neutral at the dock with no smoke
I can't imagine both engines have injector issues
But I was told some of the 6bta engines had defective injectors and we're recalled
This boat sat for 4 year with no use and I have no records on service
My last try was to pull the fuel filters and fill them with diesel engine cleaner then run the boat
No noticeable change
The black smoke seems to be more evident after we cruise for hours at 1600 rpm then advance to full power

Thanks

 

[Jetstream]

Black smoke would suggest either air supply issues or she is over propped. This is a good guide for low power trouble shooting Understanding Low Power Troubleshooting - Seaboard Marine
And it might be worth asking the question on Boatdiesel.com.

 

[123]

I would first check if the air inlet and or exhaust gas recirculation (EGR) valve are not blocked

 

[smitty477]

Hello Yoeman,


"The boat is rated to 2600 rpm and it will pull that in neutral at the dock with no smoke"
Your need to be able to reach more like 2750 in neutral as a brief high idle test.
-Are you sure your tachs are accurate before taking too many readings?
-Do you have EGT or boost readings?
-Can you confirm the turbo's operation and their output?
-Could there be blockages in the air side or on the exhaust side from 'sitting'?
- Do you have known functioning trim tabs?
- Can you move weight forward to see if that helps?


1997 was a prime year for Bayliner and others to overprop their boats as one way to achieve bragging rights in brochures and at boat shows. I think you will find a host folks with similar boats that may have ideas on this at the Bayliner site - baylinerownersclub(dot)org
Bayliner Owners Club - BOC Forum - Category Index
If you post in the motoryachts section I will be surprised if you do not eventually get feedback on that same boat with the same engines.
It would be very beneficial if you had the trans ratios on your boat handy (port and stb) as well as the details on your props (D X P X blades and materials).

Lacking any other detail but reading 1,000's of posts over at the Bayliners club over the years my best guess is that you are overloading the engines and the props are well over their desired pitch.

 

[River Cruiser]

Smitty477 has many years of experience on the proper care and preventative maintenance of boats.

 

[bilge53]

Have you contacted the previous owner? Has it ever run correctly for you? Need to determine if this is a 19 year old issue or recent.

 

[yoeman]

Good point

 

[Pau Hana]

Looking for some help to start trouble shooting
1997 Bayliner 3788
250 6bta
650 hour engines
Bottom is clean
New filters in the last 50 hours
After coolers serviced
I have no history on props but believe they are factory
The boat will not plan out and only pulls 2200 wot
14 knots top speed with 3/4 fuel not loaded
Black soot and smoke for about the first 5 minutes then it cleans up but still not getting rpm
Runs smooth and has clean airseps
Any thoughts on this would be a big help
It may be over proper or are the 3788 just under powered with the 250hp

We had the same setup on our 4087- 25 knots at WOT.

If your turbos are not spooling up, you'll have exactly the results you are experiencing.

 

[Ski in NC]

Bottom and props clean? Are you sure??

 

[yoeman]

Turbos

How can I confirm my turbos are operating No boost gauges.
It would seem unlikely both turbos are not working
No oil leaks or broken hoses filters look good
If I push the throttles full forward the rpm climb is very slow

 

[ksanders]

We had the same setup on our 4087- 25 knots at WOT.

If your turbos are not spooling up, you'll have exactly the results you are experiencing.

Pete's spot on this one.

What you are experiencing sounds like one of your turbo's is out.

Same thing happened to me on a 3488 with 315 hp engines. Was very concerning at the time.

Wont have a boat without boost and EGT gauges after that.

Down and dirty method is to pull your air cleaner and spin your turbo by hand. Should be free and easy.

 

[yoeman]

Pete's spot on this one.

What you are experiencing sounds like one of your turbo's is out.

Same thing happened to me on a 3488 with 315 hp engines. Was very concerning at the time.

Wont have a boat without boost and EGT gauges after that.

How hard is it to install boost gauges?

 

[ksanders]

How hard is it to install boost gauges?

simple. There is a air fitting on the intake manifold. Boost gauges are strictly mechanical. A little tube to the gauge is all it takes

 

[yoeman]

simple. There is a air fitting on the intake manifold. Boost gauges are strictly mechanical. A little tube to the gauge is all it takes

I will have see why the turbo isn't working
More info needed on how to see if the are running
Thanks

 

[smitty477]

Here are some benchmark numbers for the same boat and engines in a current active post on the BOC....


"2200 RPM is anywhere from 13.5 to 15 knots depending upon conditions"


Here is the entire post with more data for your type of boat and engines...


Bayliner Owners Club - BOC Forum - Topic: 3788 Cruise and Range Numbers (1/1)


Please notice that they say they need "full tabs" to get on plane and run at these speeds so if you cannot get the bow down you may be fighting the planning speed departure angle.
While it is possible that both turbo's are 'out' it is also possible that you are overpropped for your weight and weight placement. A quick way to try and prove that out is to move weight forward and also test your tabs for full movement (or any movement).
Back to turbo's - if they are spinning up to speed you will absolutely
hear a very distinct high "whine" when they are spooling over engine speeds of 2,000 rpm. You can if you like place one cheap pressure gage inline utilizing some icemaker line just to see what psi you are getting at the 2,000 rpm - find a cheap pressure gage that you can clearly read between 2 and 25 psi or so (higher is fine as long as you can read clearly down low) - I have seen them for ATV's and off roaders that read like 2-30 psi.
If you have the trans ratios and know your prop specs the folks with the exact same boats and engines will be able to help as many of them went through the exact same things over the years.

 

[bayview]

What did it do at sea trial???


If you can reach rated rpm in neutral and both engines reach the same rpm in gear when running then IMO you have a dirty bottom or over propped. Most likely over propped.
Don't mess with the exotic stuff like turbos and injectors until you can absolutely verify the current bottom and prop condition.


If you are new to salt water you may be surprised how fast stuff grows on props and bottoms. It doesn't take much to slow things down.

 

[smitty477]

"Black soot and smoke for about the first 5 minutes then it cleans up but still not getting rpm"


This 'clue' if it is accurate would leave me to believe that it is not necessarily the turbo's . If they were not spooling at all the black smoke would not get any better and in some case get much worse.
Hard to define these things from a distance as it is somewhat subjective about amounts of black smoke.

 

[smitty477]

"The boat will not plan out and only pulls 2200 wot"

If tachs are accurate and both engines are limited to 2,200 you either have two engines that are equally overloaded or two engines with similar problems.

 

[bayview]

exactly and the similar problems are usually boat related not engine related, often dirty bottom and over pitched props.

 

[smitty477]

"exactly and the similar problems are usually boat related not engine related, often dirty bottom and over pitched props."


Yes - agreed 100% , lacking more input here to be able to pin it down completely.

 

[stone beach]

you should double check bottom and prop condition, these must be clean for optimum performance.
if the boat is capable of the performance you are seeking, I have no knowledge on that score, and you are trying to get 2600 rpm at wot underway then you will need to start with around 3000 rpm at high idle (wot in neutral).
check rpm with a proper tach, not the dials on the panel, then set high idle by adjusting the stop screw on the speed control lever.
strongly advise fitting boost gauges, even if only temporary (if you dont want the panel work).
remove air filters and sea trial after all the above and record results.
if you get continuous black smoke, not just a few wisps but plenty of it, it could be turbos problem, full load boost pressure should be around 20 psi if I recall correctly for this engine.
if boost pressure is 20 or above it isnt the turbos and then either the boat is too heavy for the prop / transmission fitted...or the engines are worn out !!
you can have the latter confirmed by blow by testing.
btw, if you intend to run the boat at that speed apart from using a lot of fuel you will soon have worn out engines, if they arent already.

 

[smitty477]

"and you are trying to get 2600 rpm at wot underway then you will need to start with around 3000 rpm at high idle (wot in neutral)."


I am curious why you say this - governor 'droop' should be 60-70 rpm which will translate to 120-140 at the crankshaft.
Confirming rated rpm plus 200 should be fine - 2600+200=2800

 

[Ski in NC]

6B's with CAV pumps should be about 2900-3000 high idle if rated for 2600. Lots of droop on these.

 

[smitty477]

Thank you Ski - I have not seen that with my strobe tachs on these engines myself.
It is good to know that ...thanks