RPM Fluctuation

Sea Trial - Fail! Issue was not resolved by changing the filters one time. As I reflect on what occured, I had a glassy day last weekend and the boat ran well. Yesterday, it ran fine out to the bay, but then started acting up in the 2 footers. It dropped 200 RPM every minute or so, and sometimes dropped all the way down to 1400 RPM. Dramatic in a bad way.

Once we hit the Choptank, it behaved again with no issues. Could the boat motion be stirring up crud in my tank? I will be changing the racor again but am giving up hope of quick resolution.

Sea Ray's next step is to get Cummins out and hook the computer up to the engine and see what gives. So that sounds like missing a day of work. What a PITA. Will be testing the extended warrantee! Hopefully it is really there.

Other ideas on the table were a bad injector - nothing I can do on that one. Any other ideas?
 
This is a light grey RACOR element I removed- I assume this is not "soiled" - but I have no basis for comparison. Any confirmation appreciated. Thanks!
DSC_0055.jpg
 
vanburen said:
Other ideas on the table were a bad injector - nothing I can do on that one. Any other ideas?
Click to expand...

Sounds like a bad/loose ground with the electronic engines. You can check to see if you have any loose connections around the ECU or Throttles.
 
Filter looks ok, but to be sure shake it about 1/2 submerged in a cup of diesel and look for black "soot" to come off. Typically, a dirty Racor, dirty to the extent that enough fuel to run the engine cannot pass, is quite obvious and looks like it has been spray painted black.
 
Frank - will keep that in mind. It didn't look "bad", and changing it didn't help. Glad to hear that bad is dramatic.

Boatingfool - Will take a look at the connections. Thanks.
 
Ed,
When the Cummins tech pulled the racor elements out of my boat at sea trial they were solid black and had strings of algae trailing off the elements as they came out. Remarkably, the engines both turned WOT during sea trial with all that crap in the filters. After I shocked the tanks with biocide, installed new 30 micron filters, and ran the boat about 40 hours, I began to get RPM fluctuation in the port engine. It never dropped to 1400 from cruise RPM of 2150, but it would drop 200 RPM or so. The engine was starving for fuel. Clean filters corrected the problem. The element in the photo above looks pretty good. You may try posting over at boatdiesel.com to see what the Cummins guys there have to share.

regards
Skip
 
Any updates, did they find the problem? Hope you've got it figured out and your back to boating in tip-top shape!
 
No updates other than Cummins is coming to the boat on friday for a test run. Who wants to bet the boat will perform flawlessly while they are there?
 
ED.... BAD INJECTOR..... im sorry.... Ur going tru the same cr@p i did.... They changed the filters .. BEFORE trouble shooting ... boat ran great... next day it was a dog... there going to hook up the computer . Have no trouble codes.... tell u ur crazy. There going to drop each injector out manually tru there computer.. race the motor at the dock.... big dog and pony show . Boat will pass all the tests. They have to run the boat. U have to run the boat for them. Just hope the injector malunfuctions while they are there. They wont replace them all... SUCKS .....When they finally replaced mine the injector was DEAD stuck closed after a year of B/s... They also replaced the harness. Sorry.. id bet the bank now ...

Rob
 
Rob,
Thanks. CPS is ON THE BOAT as we speak. Initial diagnosis - before he checked anything - is that it is "surge" caused by the fuel pump rack. "We have seen this before". He said the engine, being a hybrid mechanical / electrical brute, sometimes gets confused if the rack gets out of cal. We will see. But he said it confidently!

Next steps are to check lots of things and then run the boat. More to follow. It's a nice day here and no clients are around!
 
Heck Ed, Why did i think u had QSC's in the boat ?? Crap then most of what i said doesnt apply..... ahh atleast i got to vent.... sorry for the misinfo...


Rob
 
Well, I have about 20 hrs of Boost Pressure Sensor faults which correlates pretty well with the symptoms. And that fault would cause the issue, so we will replace and see.
 
Skip-
It was Zach. Seemed very nice and capable. I had had 158 counts of a boost pressure sensor failure - fairly convincing. We swapped the sensors P/S to see if the problem moved - it didn't move but didn't reappear on a 2 hr seatrial. Am going to stock a replacement sensor and if it reappears on Port, will replace and that should solve the problem. Also updated the ECM software on both engines. Any thoughts on the CPS folks?
 
They are not cheap, but Zach has done the valve lash adjustment on my boat, was on my sea trial, and is really a good tech in my opinion. Also just a good guy. At sea trial was very patient in explaining to me everything he was doing, how the C series worked, etc. All good.
Rick from the Onan side is good for gen set work as well.

Skip
 
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