Engine Question

[LakeMichiganDave]

We have a GB with twin Cummins Cat 8.3engines. Ran 150 hours this spring on various rivers. Engines ran exceptionally. Boat sat for a few weeks with no engine start. Took our boat out yesterday and could only get up to 1200 rpm’s We like to get up to 1700 rpm’s in order to engage the turbos. We had the engine synth function engaged so 1200 rpm’s was max both engines All filters were changed in the spring. Any insights, things to check/ change? Raycore filters? Other? Thanks

 

[KnotYet]

The obvious stuff would be fuel related: bottom and props clean, fuel filters and vents.
Check tank vents or test run with the fillers open.

 

[LakeMichiganDave]

The obvious stuff would be fuel related: bottom and props clean, fuel filters and vents.
Check tank vents or test run with the fillers open.

Thanks!

 

[Comodave]

Try disengaging the synchronizer. See what happens then.

 

[DavidM]

Try disengaging the synchronizer. See what happens then.

I also doubt it is engine related. 1,200 rpm is half of rated max rpm and is very, very unlikely to be caused by fuel problems, dirty prop, etc.

David

 

[Circumnavigator]

I agree that the fact that both engines are reacting the same calls out the synchronizer as the most obvious problem.


On the unlikely, but possible side of things, you might look to see if something weird has happened to the throttle linkage that is keeping the throttles from fully opening. Also, check with a handheld tach that the tachs are honest -- (I did say "unlikely" didn't I?)



If that doesn't fix it,if you have a pressure/vacuum gauge on the downstream side of the primary fuel filters, look to see that the vacuum is within limits, maybe 4 inches or so. If you don't have a PV gauge, you should, but try shutting one engine down and seeing if the other will rev up. If it does, then I would look harder at fuel issues.


Jim

 

[Comodave]

KISS principal. Check the easy things first and the easiest thing to try is to turn off the synchronizer. If that doesn’t change the problem then start digging into the fuel supply and other things.

 

[SeaLion]

Be sure the levers are in neutral. Give a jiggle to be sure before attempting to start. Guess how I know… ;-)

 

[Comodave]

Be sure the levers are in neutral. Give a jiggle to be sure before attempting to start. Guess how I know… ;-)

The engines started just wouldn’t go over 1,200 RPM according to the OP.

 

[LakeMichiganDave]

The engines started just wouldn’t go over 1,200 RPM according to the OP.

That’s absolutely correct. Engines started, we boated for 2 hours, engines ran great, just not more rpm’s as we pushed the throttle forward

 

[Comodave]

Have you tried turning off the synchronizer? It may be that the sync has a problem or the master engine has a problem. Easy thing to try. Strange that both engines would suddenly have the same problem…

 

[twistedtree]

Also with sync off, trying running up each engine in neutral. You can run them up to full RPM - no harm. Will both go up to full RPM? Just one?

 

[LakeMichiganDave]

Have you tried turning off the synchronizer? It may be that the sync has a problem or the master engine has a problem. Easy thing to try. Strange that both engines would suddenly have the same problem…

I will try this next trip to the boat! I had a large group with me so I just want to ensure we got back to the harbor so I didn’t try anything during the trip

 

[Comodave]

Ok, let us know what happens. Always like to close the loop or keep troubleshooting if necessary.

 

[LakeMichiganDave]

Also with sync off, trying running up each engine in neutral. You can run them up to full RPM - no harm. Will both go up to full RPM? Just one?

I will try this test with engines in neutral and synch off and pushing up the throttles one at a time to check rpm levels. Thanks everyone. Appreciate all the feedback. Open for all ideas to solve this

 

[LakeMichiganDave]

Ok, let us know what happens. Always like to close the loop or keep troubleshooting if necessary.

All this discussion has been beneficial, in thinking about all the comments, it dawned on me that we have a low rpm switch, it might just be this toggle switch got pushed. Anther item to check next trip to the boat. Thanks again

 

[Comodave]

Could be. Always check the simple things before you rip into a problem. You might inject another problem…

 

[PM]

First off, Don't panic, it's a minor problem. Finding it may be a pain but I suspect fuel supply issues.

pete

 

[LakeMichiganDave]

All this discussion has been beneficial, in thinking about all the comments, it dawned on me that we have a low rpm switch, it might just be this toggle switch got pushed. Anther item to check next trip to the boat. Thanks again

Ran the engines this weekend at the dock. RPM’s reached 2000 on both engines with and with the synch engaged in neutral
It was to windy to take her out to test while actually cruising, first test yielded good results

 

[DavidM]

Not so good, actually. That engine should reach about 3,000 rpm in neutral with the throttle wide open. 2,000 rpm is way too low. Also what is a low rpm switch? Never heard of that.

David

 

[BroadCove]

Re: the low RPM switch. On my GB Eastbay 47, idle for the twin Cummins QSM11s is 700 RPM. There is a "low RPM" switch that reduces idle to 550 RPM. It's useful around docks and in no wake zones. (Although I prefer not to use it in no wake zones and instead just run on one engine at normal idle. Both engines at normal idle and slack current is about 7 kts, so too fast.)