breaker labeled "Engine Unswitched" keeps popping

[suss1173]

Yesterday I was moving a 390 with Cummins 5.9's and encountered an odd issue. Every time I throttled up to get on plain the port motor would die. When I tried to restart the motor, the engine would turn over, but it would not fire up. After some investigating I realized the breaker labeled "Engine Unswitched" in the engine room was tripped.

After resetting the breaker the engine would start right up again. However as I increased the RPM the motor would shut down again. I reset the breaker a bunch of times and it would re-start, but pushing beyond 1,250 to 1,260 was all it could take, anything beyond that RPM and the breaker would pop. I asked the owner if this has happened b/f and he said yes and that the breaker was recently replaced as well as one of the fuel pumps.

The boat is not my boat, I was moving it for someone. However, I have been thinking about a 390 and wondering what would could cause this issue.

 

[hughespat57]

Would need a little more info to better understand
Year,
Exact engine setup
QSB5.9? 6BTA?
Inline pump, rotary Bosch, common rail?

the breaker should be 15A
Simplest thing since it can be reproduced on demand is a clamp on ammeter and see if it is true over current or just a weak breaker.
If it is a real over current situation check the current draw on the pump, compare to the other engine.
Narrow down what is over current

My boat isn't diesel
But my 2001 Dodge has the 5.9 24 valve w Bosch vp44 pump
The oem electric lift pumps were marginal at best and would starve the vp44 for fuel ruining the injection pump

The marine inline injection pump is very robust
The common rail is also pretty solid system

 

[suss1173]

Would need a little more info to better understand
Year,
Exact engine setup
QSB5.9? 6BTA?
Inline pump, rotary Bosch, common rail?

the breaker should be 15A
Simplest thing since it can be reproduced on demand is a clamp on ammeter and see if it is true over current or just a weak breaker.
If it is a real over current situation check the current draw on the pump, compare to the other engine.
Narrow down what is over current

My boat isn't diesel
But my 2001 Dodge has the 5.9 24 valve w Bosch vp44 pump
The oem electric lift pumps were marginal at best and would starve the vp44 for fuel ruining the injection pump

The marine inline injection pump is very robust
The common rail is also pretty solid system

Thanks for the info. The boat is either an 05 or 06, so I believe they are the QSB motors.

 

[hughespat57]

Ok
The boat schematics only show the 15A feeds the engine harness
So I am looking for the correct Cummins engine wiring, hard to be sure...

 

[hughespat57]

To your primary question should you be concerned buying similar? No, this does not appear to be a common problem from what I am seeing.
The engine controls are pretty straight forward. This should be the breaker feeding the ignition switch and thereby the fuel solenoid and ECM. The Smartcraft has separate breaker so not related.
On this vessel I would suspect first that someone added something off that breaker not OEM
A multimeter and a decent mechanic should be able to track down loads

 

[hughespat57]

Fyi
I am retired USCG Machinery Tech
Retired ASE Certified Master Truck Tech
As i started these engines are solid
Some of the add on components like Dodge choice of the vp44 pump were bad
But the Common Rail has been pretty solid design

 

[suss1173]

To your primary question should you be concerned buying similar? No, this does not appear to be a common problem from what I am seeing.
The engine controls are pretty straight forward. This should be the breaker feeding the ignition switch and thereby the fuel solenoid and ECM. The Smartcraft has separate breaker so not related.
On this vessel I would suspect first that someone added something off that breaker not OEM
A multimeter and a decent mechanic should be able to track down loads

Ty

 

[dvx216]

Don't know anything about diesels but at an ideal the breaker doesn't trip so what kicks in when you raise the throttle 2250 RPM . Being that this is only a 15 amp breaker sounds like it would be something to do with sensors or gauges. Correct me if I'm wrong but besides the tach what builds voltage as you increase RPM. Need to at least find out what's on this circuit before you figure out where the problem might be. I know for a fact it has nothing to do with spark plugs.