Fuel pump air cylinder

jimmcld

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Does anyone know what the fuel pump air cylinder does on the NHC250? I've read how to adjust it, but I don't know what it does. Also, the adjustment procedure says to start the truck and wait until the air pressure builds up, then, open the throttle wide open and adjust the cylinder.......

Do you do this with the truck running and the throttle wide open???
 

doghead

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The air cylinder above the fuel pump, controls the auxiliary governor(used when the hydraulics are engaged for the wrecker system).

The truck needs to have air pressure built up then, you engage your pto/hydraulics(depends which model you have).

Once the hydraulics are being driven, there is an air valve that supplies the air cylinder. The air cylinder pushes the aux governor fuel stop to the desired max speed setting for hydraulics operation. My M819 is set at 1250 rpm.


Now, you pull your throttle cable out all the way and the system should hold your engine rpm, at about 1250.


This whole procedure should be in the TMs.
 
Last edited:

jimmcld

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The proceadure for adjusting it is in the TM's. However, it didn't say what it did. I understand a little better now. Instead of letting the truck go to full RPM, you bump it up against the air cylinder plunger to set at the deisred RPM when the remote throttle is wide open when working with the boom.

By the way, I have an M816.

Thanks for the reply,

Jim
 

chrsbb19

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Ok, soI have an M816 and all the sudden the darn valve goes max extend the instant the pressure is charged and stalls the motor. i pull max throttle and it barely idles, im not using the hydros or the pto. i didnt adjust it, touch it, or even look at it. I finally got to drive it and out of nowhere BAM! then im limping back, in first gear, 4mph max... Any suggestions?
 
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Csm Davis

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Ok, soI have an M816 and all the sudden the darn valve goes max extend the instant the pressure is charged and stalls the motor. i pull max throttle and it barely idles, im not using the hydros or the pto. i didnt adjust it, touch it, or even look at it. I finally got to drive it and out of nowhere BAM! then im limping back, in first gear, 4mph max... Any suggestions?
Make sure the rear pto next to the door is disengaged and locked in position then check the little valve that engages the air. Sounds like one of them moved or failed.
 

chrsbb19

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ok so it was the crane engagement handle by the rear winch. Disengaged the crane and now i have full throttle back, but now i cant use the crane. im going to adjust the valve and see what happens.
 
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