Northern Lights genset problem

[Terry B]

Recently purchased a boat with a 10 year old genset. Had oil/filters/impeller changed before delivery.
Starts and runs fine with or without load for 5 or 6 minutes, then shuts down.
Good raw water flow, plenty of oil and water, and nothing seems hot.
Will restart, but stops again as soon as the "preheat & shutdown bypass" switch is released.
If I wait 5 or 10 minutes before restarting, it will run a couple of minutes.
My mechanic said that all of the temperature/pressure sensors have to connect to ground to prevent shutdown, and he said they were.
1. Anyone have any ideas? I can provide model # and other info.
2. Is this the best forum to ask this type of question?
Thanks - Terry B

[Alan Wheeler]

There are many possibles. I suggest you may have a faulty sensor that is then causing the safety to shut the engine down. I assume there is an electric soliniod that does this?? The bypass switch is doing just that. It is bypassing the sensors. You need to test each sensor by attaching a probe and seeing which activates. Then you need to check why. Is it the sensor or is there an engine issue. The sensors I would imagine being the issue will be Oil pressure or water temp.
The easiest way of checking is to fit a gauge to both oil and water and see what is actually happening.
Another simple test is to ensure you have good clean and correct viscosity oil and clean filter. It maybe that the oil is too thin when hot reducing pressure to much.

[AnchorageGuy]

Most times, but not always we see this issue the problem is in the circuit board. If you can get your hands on one just to test that would help. Next step would be the sensors. One other thing to look at is if you are connected to a fireboy system. The unit should give you some kind of code at shut down. If it has an LCD which I doubt, you will get a code, but more likely there will be a serials of lights flashing either on the circuit board or on the start up switch depending on the set up. That code will indicate what is happening.

[Terry B]

Thanks for you speedy inputs! There are no codes on this model.
The mechanic I hired confirmed new filters, oil looked clean with OK viscosity, and infrared temp of hot water side 75 deg at shutdown. He also suggested the circuit board, so I will get an electrical guy to take a look.
Troubleshooting would be fun if the thing were on a stand in the garage, not buried in a hole in the water!
Cheers - Terry B

[AnchorageGuy]

Terry, Be careful of having an electrical guy "troubleshoot" since most don't know a lot about circuit boards. Make sure they understand the problem and have experience diagnosing the board. You need a genset tech and not just a mechanic. What they ALL do here is simply swap out the board, they all carry test boards, and if all works then replace it. Just don't want to see you throw money away.

[hellosailor]

"My mechanic said that all of the temperature/pressure sensors have to connect to ground to prevent shutdown, and he said they were."
Is he intimately familiar with that genset?

Typically (not universally, but most of the time) temperature and pressure sensors are simply variable resistors, with the majority of them having a resistance range from 40-240 ohms in the "operating" range. And again typically, most of the drop to 40 ohms in the "overheat" or "low pressure" condition. A true zero ohm reading to ground would be unusual--unless the sensor had shorted out internally.

I would suggest getting the correct technical information for your genset, either from the maker or whoever makes the senders, and checking them with an ohm meter to make CERTAIN of how this one is supposed to run--and how it is running.

I'd agree that something which the "bypass" switch normally bypasses, is defective. A very likely situation would be that the bypass switch DISconnects the oil pressure sender, allowing the genset to start up with zero oil pressure. If that sender was faulty...as soon as you released the bypass switch the genset would cut out.

Most likely it is something that simple, and if it is just a sender (sensor) then you need to confirm whether those sensors should ever be generating a ground, or what their correct operation is. Once you've done that--you may be able to test and confirm the problem by something really simple, like unplugging the lead to the sensor, or ground the lead to the sensor. (But don't just ground things unless you know that's going to be safe.)

One thing I've learned, is that you never can be sure a safety mechanism (like a sensor) is working properly. Or, that any given maker used "typical" parts. Some of them seem to go out of their way to use totally atypical ones.

[GordMay]

Some generators use a fuel solenoid valve to cut off the fuel supply and shut down the engine if a key is turned off or low oil pressure occurs.

Whenever a diesel stops running, it's often due to a fuel supply problem.

Starting does not require as much fuel as running at full RPM. Often a magnetic fuel solenoid that does not open completely will result in fuel starvation.

I would also check to ensure that the fuel tank vent hose is unobstructed - any restriction here and a vacumm is created in the tank.

North American Oil Pressure Senders are either 33.5 Ohm (80 psi) to 240 Ohm (0 psi), or 88 Ohm (400 psi) to 1 Ohm (0 psi).
European Senders are 180 Ohm (80 psi) to 10 Ohm (0 psi).

See my Gallery (page 7):

Testing Engine Gauges
http://www.cruisersforum.com/gallery...r&imageuser=79

Testing Engine Gauges (2)
http://www.cruisersforum.com/gallery...r&imageuser=79

Engine Gauge Wiring Diagram
http://www.cruisersforum.com/gallery...r&imageuser=79

[never monday]

NL likes to use relays