NHC-250 Dies at extended idle.

[rhurey]

My NHC-250 will drive great, but sometimes after idling for ~10-15 minutes it'll die. Especially frustrating when it's idling so I can run a crane off the PTO. No issues driving.

About 1/2 the time it'll fire right back up if I try, sometimes I can crank away with no luck. But wait ~5 minutes and it'll fire no problems.

Changed the fuel filter, no difference.

Any ideas?

 

[simp5782]

My NHC-250 will drive great, but sometimes after idling for ~10-15 minutes it'll die. Especially frustrating when it's idling so I can run a crane off the PTO. No issues driving.

About 1/2 the time it'll fire right back up if I try, sometimes I can crank away with no luck. But wait ~5 minutes and it'll fire no problems.

Changed the fuel filter, no difference.

Any ideas?

Hook a test light up and lay it so it is laying on the fuel shut off solenoid wire. When the truck dies see if the pcb is dropping the power to it causing it to die. If not then replace the fuel shut off solenoid. You can also pour cold water on the pump when it is only spinning over and wont start and see if the pump is overheating. Should start up after the water is applied if thats it.

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[doghead]

Replace your rubber fuel lines

 

[JDToumanian]

Related to Doghead's rubber fuel line suggestion is the tank switching valve and/or primer pump... Either one may be allowing little bubbles of air to enter the fuel lines which can stall the engine. The valve can be rebuilt by replacing the o-rings inside, there's a thread on it here somewhere.

Jon

 

[Floridianson]

I would test the solenoid buy screwing in the thumb screw and see if the problem went away. Mine went bad and would not start.

 

[jcappeljr]

Sucking air someweres..

 

[162tcat]

It's an air leak problem. Replace fuel lines if you haven't, rebuild or abandon the primer pump and make sure you replaced the small o ring at the bolt on the filter. My filter housing never sealed up right so I replaced with a spin on and have never had an issue since.


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[WillWagner]

Sucking air will cause a slow shut down, the rpm will surge and the idle gets real low, then it dies. If it is idling normally and dies like you shut the key off, it is either being told to turn off, like maybe the PCB or a loose connection in the ignition circuit, the FSOV on the pump is not rapid re start type so if it looses b+ at all, the engine will die and not re start w/o the starter, or a failed FSOV, same thing, it will die and only re start by craking it. When it dies, remove the wire from the FSOV and check the resistance from the stud to a ground, IIRC, 24v coils should be in the 24 to 50 ohm range. any more or less, the coil is failed.

My guess is a FSOV.

Here are the specs....

1 to 5 ohms for 6-VDC solenoids
6 to 15 ohms for 12-VDC solenoids
24 to 50 ohms for 24-VDC solenoids
42 to 80 ohms for 32-VDC solenoids
46 to 87 ohms for 36-VDC solenoids
92 to 145 ohms for 48-VDC solenoids
315 to 375 ohms for 74-VDC solenoids
645 to 735 ohms for 115-VAC solenoid

 

[rhurey]

Here's a video of it dying: https://1drv.ms/v/s!AnhaA1TwRcf6lac7cgM0BQ-_Ga2gWw

My first thought was the fuel filter, but it wasn't that. Thought air, but I'd have expected trouble starting after sitting instead of inability to start after it dies, but works great after sitting.

Overheating shutdown solenoid fits the symptoms. And explains why it felt like the MTTF went down as the day went on. (And my patience for waiting between starts also dropped.)

 

[simp5782]

As quick as it turns off its the fuel solenoid. You can try pouring cold water on it and see if itll come back on right after you do. It is the best test. Used to have to do that on old DB2 IDI pumps.

 

[WillWagner]

Shuts off like no go juice. When it shuts down, turn the manual knob in and see if it starts. If so, time for a FSOV.

 

[Floridianson]

Got to love the 250 with the thumb manual screw but keep some lube spay on it so it works easy when needed. Any trouble with the fuel solenoid or the PCB then break out what a good mechanic has in his truck. Remote starter button and learn what wire is the starter solenoid trip and you can get them started. Yea heard people say I can do it with a screw driver but you could run the risk of doing damage to the threads on the solenoid or starter and make trouble for the next guy that has to remove the starter. Don't cheap out buy the remote button.

 

[rhurey]

Solenoid for sure.

Was moving firewood for the neighbor and got the first bag lifted and it shutdown. Turned in the override screw and it fired on the first crank. Kept running till I had it back home and undid the screw. Died instantly.

Thanks folks. Of course, I just fixed a leak in the emergency shutoff by replacing it and adding the dual fuel line. Should have tracked this down while I had that all off. Oh well.