NHC 250 Fuel Priming Pump

[brock]

Hello All,

Recently purchased a '85 M936A1 Wrecker with a NHC 250.

It had not run in over 2 years. I went through and replaced the fuel filter and oil filter and drained/replaced oil and fuel.

The fuel primer pump works but only barely. Seems like the internal seals aren't sealing as well as they could. I got the truck started but I think I may be sucking air through the primer pump. Is there a rebuild kit for this unit? Also, the emergency fuel shut off valve that sits at the top of the pump in the high pressure line is leaking like a sieve. Any ideal on how to rebuild or replace?

Another question, what would cause a severly lazy throttle response? I push the pedal to the floor and its a good 1-2 seconds before there is any increase in throttle. Im hoping this is attributed to air being in the system.

Any and all info is greatly appreciated.

Thank you

 

[M35A2-AZ]

The Primer pump only has two or three o-rings in it that can be replaced.
It does sound like the motor is sucking air.
You need to check your fuel lines, fuel filter seal, etc.

 

[Csm Davis]

Hello All,

Recently purchased a '85 M936A1 Wrecker with a NHC 250.

It had not run in over 2 years. I went through and replaced the fuel filter and oil filter and drained/replaced oil and fuel.

The fuel primer pump works but only barely. Seems like the internal seals aren't sealing as well as they could. I got the truck started but I think I may be sucking air through the primer pump. Is there a rebuild kit for this unit? Also, the emergency fuel shut off valve that sits at the top of the pump in the high pressure line is leaking like a sieve. Any ideal on how to rebuild or replace?

Another question, what would cause a severly lazy throttle response? I push the pedal to the floor and its a good 1-2 seconds before there is any increase in throttle. Im hoping this is attributed to air being in the system.

Any and all info is greatly appreciated.

Thank you

The primer pump just has an O-ring to replace but sometimes you can just tighten it a little bit and or put a little silicone grease on the shaft to get it to seal off better. Also check the plastic line going to the primer pump they are often cracked. And yes air will make it slow on the accelerator. I would advise you to replace all of the plastic and rubber lines in the fuel system.

 

[brock]

My hope is to remove the primer pump and pick up new o-rings at a NAPA then reinstall.

I found two of the fuel supply lines under the dash that connect to the fuel tank selector to be leaking severly. Going to have two new lines made.

Any ideas where to get a replacement emergency shut off valve? Anyone have a good used one?

 

[tractors0130]

Hello All,

Recently purchased a '85 M936A1 Wrecker with a NHC 250.

It had not run in over 2 years. I went through and replaced the fuel filter and oil filter and drained/replaced oil and fuel.

The fuel primer pump works but only barely. Seems like the internal seals aren't sealing as well as they could. I got the truck started but I think I may be sucking air through the primer pump. Is there a rebuild kit for this unit? Also, the emergency fuel shut off valve that sits at the top of the pump in the high pressure line is leaking like a sieve. Any ideal on how to rebuild or replace?

Another question, what would cause a severly lazy throttle response? I push the pedal to the floor and its a good 1-2 seconds before there is any increase in throttle. Im hoping this is attributed to air being in the system.

Any and all info is greatly appreciated.

Thank you

There are 2 O-rings that measure 3/8 x 1/2 x 1/16 wide towards the end of the primer plunger after you remove it.
I had just replaced mine that were sucking air along with the supply hose from the fuel filter to the IP that was also leaking.
The truck would surge up and down while it was at an idle, after these were changed the idle smoothed right out and was no longer surging.

 

[brock]

That's great to hear. Mine is doing the same thing. Surging at idle.

Where did you source your O-rings from?

 

[WillWagner]

Look in the 5t up manual section. There is a parts manual there that you can get the correct O-rings and shut off from Cummins.

 

[brock]

Look in the 5t up manual section. There is a parts manual there that you can get the correct O-rings and shut off from Cummins.

Will do, Thanks! @WillWagner

 

[Monkeyboyarmy]

My hope is to remove the primer pump and pick up new o-rings at a NAPA then reinstall.

****Remove the pump completely so that you can remove the 2 slotted plugs that hold the check valves and springs in place. Clean and re-install. I am pretty sure that when you lock the handle it closes the port with a needle and seat so there is no leakage.

I found two of the fuel supply lines under the dash that connect to the fuel tank selector to be leaking severly. Going to have two new lines made.

****There are no fuel lines under the dash. The selector on the dash is only for the guages. The selector that is to the left of the drivers seat is troublesome at times. More often is the rubber lines deteriorated.
Any ideas where to get a replacement emergency shut off valve? Anyone have a good used one?

****There is an o-ring between the pump and fuel shut-off valve. Any idea where it's leaking?

 

[tractors0130]

That's great to hear. Mine is doing the same thing. Surging at idle.

Where did you source your O-rings from?

You can go to any auto or truck parts store and buy the o-rings as long as they are compatible with diesel.

 

[DeeMan6996]

Petcocks.

When I purchased mine and got it trucked back from Saint Louis to my place I went through and changed the fuel filter, oil, and oil filter. I filled the fuel filter bowl up with fresh diesel and primed it. The ol small cam Cummins fired right up after one crank, and took the oil pressure a couple of seconds to reach operating psi. I decided to let it sit and idle for a while.

It ran for 4-5 minutes then died. I removed the fuel filter bowl and saw that all the diesel had been sucked out of it with no fuel going into the bowl from the tank. I filled it with fresh diesel again and then I put an air blow gun in the tank and had a buddy standing by the fuel filter bowl and said that the petcock in front of the fuel filter was hissing badly. So we put a bolt (Don't remember what size) in the hole and never had a problem with air in the fuel lines again. But then I had to do an overhaul so...

All in all just check the petcocks and make sure none of them are sucking air. My primer pump was still working as should so I couldn't tell you how to rebuild that but just my

Good luck!

 

[brock]

****There is an o-ring between the pump and fuel shut-off valve. Any idea where it's leaking?

Fuel is leaking from the shaft. I removed the arm and could see a steady stream.

 

[brock]

When I purchased mine and got it trucked back from Saint Louis to my place I went through and changed the fuel filter, oil, and oil filter. I filled the fuel filter bowl up with fresh diesel and primed it. The ol small cam Cummins fired right up after one crank, and took the oil pressure a couple of seconds to reach operating psi. I decided to let it sit and idle for a while.

It ran for 4-5 minutes then died. I removed the fuel filter bowl and saw that all the diesel had been sucked out of it with no fuel going into the bowl from the tank. I filled it with fresh diesel again and then I put an air blow gun in the tank and had a buddy standing by the fuel filter bowl and said that the petcock in front of the fuel filter was hissing badly. So we put a bolt (Don't remember what size) in the hole and never had a problem with air in the fuel lines again. But then I had to do an overhaul so...

All in all just check the petcocks and make sure none of them are sucking air. My primer pump was still working as should so I couldn't tell you how to rebuild that but just my

Good luck!

Thanks! That's a good idea.

 

[Floridianson]

I got tired of pumping the 250 primer/ filter canister and bought a electric diesel pump. Up graded the rubber hose and bought a hydraulic fitting that pushes into the ribber line and the fuel line from canister screws on to it.. I undo the fuel line at the elbow of the PT and hook it to the pump. Fire up pump and ten seconds later full canister and line.

 

[ksev62]

Search for P/N MS29513-012 on Amazon. Those will work just fine!