QSM11 port motor will not go over 1280 rpm

D

Dewbert

New Member
Jan 1, 2024
10
Middle River, MD
Boat Info
480 sedan bridge 2002
Engines
Cummins QSM11
Just bought a 2002 for 80 sedan bridge with QSM 11’s in it. We ran about 70 miles and at that time we were running about 1600 RPMs due to some rough weather, and all of a sudden the port motor reduce itself to 1280. We reduce the power to an idle, took it out of gear, and the port motor ran the RPMs all the way up. Put it back in gear and the port and starboard motor rpms rose all the way up just like it should up to 1280 and then the port motor stoped there. The starboard motor continued higher but as i pushed the port throttle higher there is no response.
At the time the engine synks were on, but there was no difference whether the engine synk was on or off The port motor will still not go higher than 1280. (when we first tried to use the engine sink initially it didn’t work we had to turn it back off back on back off and back on again and then it started working). The boat is equipped with cruise and the cruise switch was in the off position.
we pulled into a marina changed all the fuel filters still had the issue so we had a diver. Check to make sure we didn’t have anything wrapped around the shaft or the prop. Nothing was there, but the driver did find that the sink on the shaft on the port side was loose and was down in the cutlass bearing and was wearing a ring around the sink. I don’t really think that’s the issue. Has anyone ever seen this before or know what it could be?
 
With regard to the zinc on the shaft that is loose; you should have it put back in its original position or take it off all together. By sliding down and laying on the front side of the cutlass bearing, you are inhibiting if not blocking water flow around the shaft through the cutlass bearing. That is the cooling medium. If not properly cooled, the cutlass bearing will quickly wear out resulting in excess play of the shaft.

I don't have anything to offer on your port engine rpm issue. Are there any alarms that have gone off on the engine electronics (smart craft, etc)?

Jaybeaux
 
Yes the diver put a new one on in the correct position.

no alarms no vibration nothing. i had a CAT mechanic on board when it happened he plugged in his laptop and no codes. He had the program insight to read codes. We didn’t have time to do much else as we were waiting for a diver.
also when at the 1280 rpm’s the load was the same on both motors
 
I had very similar symptoms on a QSB engine a couple of years ago; no alarms or codes either. Turned out the turbocharger wasn't able to engage. I wasn't there when it was fixed but I think the cause was one of the turbo air fittings coming loose.
 
The turbocharger may have seized or as @alnav says the rubber coupler may have ruptured. Take the air filter off and spin the compressor wheel with your finger. Pic of that coupler below. But the scan would have seen a mismatch in throttle setting and engine power/manifold pressure.
Since it hits an RPM "wall" then I wouldn't suspect a fuel issue. The Cruise setting would affect both engines. The only other thing is there is a governor in the injection pump that limits maximum RPM - that may have issues - like broken springs.

IMG_4579cropped.jpg
 
I have QSC’s but when we did sea trial the port side would not go over 1220. Cummins Tech had a laptop plugged in and saw no codes. Turns out these engines have Cummins cruise control. That was limiting the RPM on the port side. When we turned cruise off, both engines went to rated RPM. Also figured out that the stbd side cruise is disabled because the ECM was replaced and not programmed properly.
 
Richard Carlisle said:
I have QSC’s but when we did sea trial the port side would not go over 1220. Cummins Tech had a laptop plugged in and saw no codes. Turns out these engines have Cummins cruise control. That was limiting the RPM on the port side. When we turned cruise off, both engines went to rated RPM. Also figured out that the stbd side cruise is disabled because the ECM was replaced and not programmed properly.
Click to expand...
Thanks
 
ttmott said:
The turbocharger may have seized or as @alnav says the rubber coupler may have ruptured. Take the air filter off and spin the compressor wheel with your finger. Pic of that coupler below. But the scan would have seen a mismatch in throttle setting and engine power/manifold pressure.
Since it hits an RPM "wall" then I wouldn't suspect a fuel issue. The Cruise setting would affect both engines. The only other thing is there is a governor in the injection pump that limits maximum RPM - that may have issues - like broken springs.

View attachment 156212
Click to expand...
Thanks for the info
 
Lets start at the cheap and easy stuff first.

Lack of fuel flow would give this type of issue on any diesel engine. If this a new to you boat I would inspect/replace the fuel filters..Racors and secondary on engine if there are any.

If there is any water in the Racor separator or its full of gunk, you'll need to treat the fuel, and keep replacing filters until they run clear. There is a Diesel Fuel Management write up that most CSR diesel owners would recommend you implement and follow.

 
@Dewbert I would seriously look into the Cummings Cruise Control settings. Also pull the air cleaner and turn the turbo vanes by hand and and note if they spin freely or have binding of some sort, while there look at the output for tares in the hose. But I doubt it's a turbo if ~1200 RPM is all that can be reached. Turbos don't usually come into play until ~>1400 RPM unless it's blocked somehow.

If fuel were the issue I suspect the engine would show other signs, like stalling and/or heavy smoke.
 
If it’s a turbo it should rev higher under no load. If it still hits the exact same RPM unloaded as loaded, I would look more to electronics, like cruise control.
 
Unless there are ECM issues on one of the engines then the C-Cruise can't be the issue.
C-Cruise sets maximum RPM for BOTH engines. Press Cruise 1 or Cruise 2 and advance the throttles fully. The engines will not exceed the C-Cruise set point.
If Sync is on when engaging one of the Cruise modes then advancing only the port throttle is required.
To adjust one of the Cruise modes turn the mode on then press the RPM+/- switch to raise or lower the set point. Both engines will take the new set point as well as the Cruise mode remember that set point.

The crux of this, however, is the C-Cruise is unlikely to be the issue.
 
ttmott said:
The crux of this, however, is the C-Cruise is unlikely to be the issue.
Click to expand...
It’s the easiest thing to eliminate just by turning off cruise. On my boat, sync must be on in order for cruise to work. If an ECM has been replaced, there is a possibility that it was mis-programmed. The local cummins tech told me that cruise limits the RPM on one engine and sync matches the other engine to the one on cruise and all of that magic happens in the ECM’s.
 
Thanks, everyone for your input. We took all this knowledge drove three hours back to where we had left the boat, and since we had already changed all the fuel filters we checked for leaks, check the turbo checked the cruise everything checked out. We decided to take it out and see trial it and everything worked as it should we continued our trip South to bring her home and after about two hours of running it happened again. port motor wouldn’t go over 1300 RPMs. It was a quick diagnosis and fix it needed a new boost sensor.
Thank you everyone for your reply and input it really helped us eliminate other issues and diagnose the real problem.
 
Dewbert said:
Thanks, everyone for your input. We took all this knowledge drove three hours back to where we had left the boat, and since we had already changed all the fuel filters we checked for leaks, check the turbo checked the cruise everything checked out. We decided to take it out and see trial it and everything worked as it should we continued our trip South to bring her home and after about two hours of running it happened again. port motor wouldn’t go over 1300 RPMs. It was a quick diagnosis and fix it needed a new boost sensor.
Thank you everyone for your reply and input it really helped us eliminate other issues and diagnose the real problem.
Click to expand...
but, didn't that show up on the Diesel View as a fault? Does that boat have Smartcraft and Diesel View? 2002 was a transition year....
 
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