Latest addition: M931A1 (question about NHC 250)

[zguinness]

Made the trip last week with my father-in-law to pick up 2 more trucks. I drove the M931 home and only had one minor hiccup. About 1/4 of the way into the trip, the driver's side wiper blade fell off (of course it was raining).

I really like the way the 931 drives compared to the 923. Much more giddy-up on takeoff.

I have a question for some of you with more experience with the NHC 250 engine. I was using the hand throttle... would pull it out one click and RPM would slowly increase, pull it out another click and RPM would slowly increase, pull it out another click and RPM would jump up very quickly.

Also, when I parked it in front of the shop I put her in neutral and engaged the parking brake. Suddenly my RPMs shot up. I quickly dropped her back into 1-5 and it kinda "jumped" forward a bit. Then I put her back in neutral and the RPMs stayed at idle.

It's almost like there's a tendency for the engine to "overspeed" at certain points.



Oh... I did find the wiper blade:

 

[doghead]

The idle will run up, when you use the hand throttle. That's the way the NHC250 is.

You could have an air leak in a fuel line.

 

[zguinness]

This thing shot up when I used the hand throttle. The first click wasn't much, second click not much, third click it started climbing quickly and didn't look like it was going to level out so I slammed the throttle back in and left it alone.

It happened with the hand throttle, happened when I put it in neutral to park, happened one or two other times randomly... RPMs would just shoot up.

I tried searching around a bit and found something about air in the fuel lines. I'll look into that when I get a chance.

 

[EMD567]

Air leak.........Check the fuel selector switch, or the flexible line from the filter to the IP.

 

[zguinness]

Air leak.........Check the fuel selector switch, or the flexible line from the filter to the IP.

Will check. Thanks for the advice!

 

[doghead]

If your saying that your just trying to use the hand throttle to idle it up a bit(above idle to 1400 rpm, then yes it is normal to see the motor rev up on it's own .

All of mine do this. It's not an air leak, imho.

 

[Rifleman]

When i fire up my truck in the driveway with the Cummins 250 and am warming it up i use the hand throttle too. Mine will do the same thing your talking about, first click no change in RPM's, next click a little change in RPM's, next click a little more change in RPM's now turning around 750 to 850 RPM's, next click it will jump all the way up to 1500 to 1700 RPM's. So it would seem that this is normal with these trucks while using the hand throttle.

 

[Castle Bravo]

The two trucks I had with NHC250s also did what is described here. The hand throttle control is almost useless for unattended high idling.