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Old 10-20-2017, 03:22 PM   #1
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Default Engines start, but won't stay running.

Cummins 330 diesels ... will crank and run as long as they key is held in the start position, but engines stop as soon as key is released. Thoughts?

Thanks in advance.
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Old 10-20-2017, 03:49 PM   #2
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Bad ignition switch?
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Old 10-20-2017, 03:51 PM   #3
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This is a typical Diesel safety mode. The diesel will cut power to the fuel pump if one of the many sensors is tripped or fails. In this case it is occurring on BOTH engines? That would be unusual. It's commonly just a bad sensor.

Do you have a service manual? There is usually a troubleshooting flow chart.

You can start by putting 12v power directly to the fuel pump, make sure it's running, discharging water and oil pressure is good.

Otherwise, you would need to short out each sensor individually. Once shorted, the signal goes to the next sensor inline. The problem is tied to the sensor that is shorted when the engine starts. Try replacing that sensor first. If the sensor replacement doesn't fix the issue, then it is a real problem related with what that sensor is monitoring. (i.e. short the oil pressure sensor and the engine runs. replace the oil pressure sensor. If the problem persists, you have an oil pressure issue. If the problem is resolved, you had a bad sensor).
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Old 10-20-2017, 04:23 PM   #4
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Both engines, same issue. Batteries were off charger for about five days post IRMA ... but have been back on charge since then. The fact they crank seems to lead me to thinking the batteries are ok (separate battery for each engine/starting).
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Old 10-21-2017, 02:55 PM   #5
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Thanks for all the inputs ... trouble shooting begins as soon as I can carve sometime for the boat. Will let you know what I find.
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Old 10-23-2017, 02:35 PM   #6
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Do you have separate Racor's for each engine? Or do both engines pull through the same filter? A bad sensor on one engine will not impact the other. The problem has to be upstream. I wonder if you've someone introduced air into the fuel system. Are the fuel cocks closed? fuel return cocks closed? Did you replace fuel filters recently?
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Old 11-17-2017, 11:37 PM   #7
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Update ... fixed and back up and running.

Folks pointed out that while the starter motors would roll the engines, they really wouldn't start. Recommendations were to focus on 'safety' interlocks, things that are overridden when the starter motor is cranking, but which 'safe' the engine (won't allow them to start) when they tries to run by themselves. Oil pressure, and temperature sensors were some of the recommendations.

Turns out a safety interlock was the culprit, my FireBoy system. During Irma it appears water got under my covered helm/dash and 'filled' the FireBoy's box connector box. As you can see in the picture, it was basically on 'slow simmer'.

Replaced the box at the helm and ran new wires to the unit in the engine room and everything's fine now.
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Old 11-18-2017, 04:34 AM   #8
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Interesting failure, glad you figured it out.

Is the box supposed to be waterproof?
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Old Yesterday, 02:17 PM   #9
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Thanks for the follow-up!! I'm glad you found it.

It looks like it got fried around "Aux Inputs"? (Tough to read) Did the water cause a short?
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Old Yesterday, 07:30 PM   #10
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Quote:
Originally Posted by mmwjr View Post
...Is the box supposed to be waterproof?
I'd say water resistant, but certainly not water tight. Designed to be mounted 'at the helm' so you'd think it would be tighter.

Quote:
Originally Posted by shrew View Post
... It looks like it got fried around "Aux Inputs"? (Tough to read) Did the water cause a short?
Correct, that terminal pair connect the bilge blower switch to the bilge blower (don't want to have the blower on if there's a fire down there). My guess is that every time I switched on the blowers, before trying to turn the engines, I was partially shorting at that connection.
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