Gunked up injector pump on NHC 250

[LCA078]

My M923 with NHC 250 has been sitting a while from a crank-no start issue and I've confirmed I have no fuel coming out of the fuel shut off valve when cranking. Here's what I've done so far:
-Verified adequate fuel flow to pump by pressuring fuel tank with 10psi so I don't think it's a fuel supply issue.
-Disconnected injector line out of top of the pump and verified no fuel when cranking.
-Removed manual fuel cut-off valve and verified no fuel coming out of fuel cut-off solenoid.
-Verified 24v to solenoid when start switch moved to Run.
-Removed solenoid valve and verified correct operation by blowing through it while Soldier B turned start switch to Run. I didn't hear a "click" like I thought I should when powered but it seemed to work fine with the old mouth-blow test.
-Paused here for a scientific discovery that when you're sitting on the left front tire, holding onto the engine with your left hand so you can get your head inside the engine bay to put your lips on a fuel cutoff solenoid that's removed from the IP but still connected to electrical system for the blow test and you give Soldier B the signal to move the start switch to Run, you are actually completing a 24v electrical circuit with your lips.
-Gave time for Soldier B to stop laughing hysterically when they figured out my shocking discovery.
-Verified no fuel coming up through IP port where solenoid mounts when cranking.
-All the time there was a very slight seepage of fuel coming out which I assume was from the pressurized inlet. But cranking didn't change the flow rate on this seep so I'm assuming something inside the pump is stuck closed.
-At this time, I ran out of daylight and called it quits.

The other thing I need to mention is this fuel system was/is filthy. When I bought the truck a number of years ago, the fuel smelled like varnish even though it started and ran fine. It was an auction truck so I have no idea what was run through it. When I changed out the fuel filter, the canister inside walls were caked in some brown tacky goo that easily washed off with a can of parts cleaner but it really made me wonder what was throughout the fuel lines, tank, IP, etc. Anyway, I started having a die-on-deceleration problem that turned into a hard start problem so it sat for a bit until now. I changed out the rubber lines but now it's a complete crank-no start with no smoke. When I pulled the manual and electric fuel cutoff valves off, I noticed a thin film of that brown goo again so I'm assuming the IP is just gunked up with same stuff. That goo washed off easily with Chemtool B12 but it really bothered me to see it in there.

So lots of rambling to know how I got here but here's the point of this thread: What's the best way to clean my IP? I plan to connect a garden sprayer to the inlet and pressurize with 1 gallon of diesel mixed with a heavy dose of injector cleaner, B12 and Seafoam witches brew and let it seep up through the IP and out of the top solenoid that's plumbed into a catch pail so none of it goes into my injector lines. Maybe this will help clean out something but is there anything else I can do? Move the accelerator lever back and forth and crank the engine for a bit? I don't know of any other movements I can do to help free up inside parts. Are there any ports I can use to better push the witches brew through to help free up the inner guts?

 

[WillWagner]

First thing is to remove the inlet fitting at the rear of the pump and use a mirror to look inside the hole. Have "soldier B" crank the engine and you watch the gear pump teeth turn. If they do turn, the gear pump is not broken.

On top of the pump is a large plug with a slot in it. There is a filter under that plug. It's purpose is to stop any metal that might occur when/if there is a malfunction inside the pump from getting into the injectors, however, if the fuel system is gunked up, that screen filter can plug. It can be cleaned if it is just goo in the system, but, if there is metal in it, it is next to impossible to clean due to a magnet being inside the filter. The flow through the filter is reverse from any other filter, it flows inside out instead of outside in.

If the pump is gooed up, you might be able to drain the pump anf then fill it with mineral spirits. There are two plugs, maybe 3, I am kinda forgetting these things, on the bottom of the pump body. You can remove the plugs, no parts will fall out, take the fuel shut off off so the pump vents, and drain the body. Re install the plugs and fill the body via the FSOV port or the screen filter hole, that is easier and does a better job at getting things down in all the little passages.

Let things sit for a day or so, drain it, put it back together and see what happens.

No bleeding necessary, the PT pump will suck a head of fuel 30 feet vertically. Just crank it, it will take a bit but if the pump is not messed up inside, it will lite.

I read you pressurized or put air in the tank, fuel did get to the pump inlet, correct?

 

[LCA078]

Hi Will-

Thanks for jumping in. I followed your advice in this thread, post #3 about divide and conquer the system. https://www.steelsoldiers.com/threads/cummins-pt-pump-diagnostics.196616/ When I pressurize the tank I have pretty good fuel flow out of the IP inlet supply line from the frame mounted filter which is what led me here. I still have a few tweaks to do to the supply side but there is more than enough fuel for IP to work.

I understand everything you're saying and will try those when I can get back to the truck (it's a couple hours away at my dad's shop).

I do have a couple clarifying questions:
-I tried to remove the large plug on top of the IP but it didn't budge. I read a trick on SS about sticking a washer in the slot and using pliers instead of a screwdriver but all I did was bend the washer. Any tricks to getting the plug out without butchering the top of it?
-For plugs at the bottom, I think I know which ones you're referring to as they look like little pipe plugs with allen head tops, right? Are those plugged lines from when they drilled out the internal passage lines or do they drain the body? I guess what I'm asking is I don't know what's in the space where the fly-weights rotate? Are those lubed by engine oil or is it a dry area that drains any fuel seeps into the crankcase or such? I can't imagine the fly-weights spin in full bath of diesel but I could be wrong.
-I'll check the gear pump is moving when I crank but I can't imagine it would be broken. But hey, who knows what may have got sucked in to jam a gear pump.

BTW- for others who read this thread and don't know much about these pumps, I watched two videos to visualize how these pumps work:

A really good and concise animation of the pump internals.

A long video that shows the pump being taking apart, rebuilt with new parts, and then tested. Not the best video for troubleshooting but it shows the parts and how they work together.

 

[WillWagner]

The plugs are there so that fuel can be drained as to not make a giant mess when servicing and I think a troubleshooting port, although I have never used it. IIRC when the pump is on the stand, there is a fixture installed into one of them, and to use accessories like a high idle governor. One or two of them are just into the body, one is a pressure port. Back in the day, guys that hauled asphalt would plumb a line from the pressure port to a sprayer to coat the dump box so the product would slide out and not cake the box up.

The fly weights are running in fuel, there is no engine oil inside the pump, fuel is it's only lube source.

I do not remember how the NHC pump inlet is configured. If the inlet fitting is straight, easy enough, just unscrew the fitting. If the fitting is a 90 degree, the damper will need removing. If that is the case, the two allan head capscrews closest to the inlet fitting need removing, just these two long ones.

As for the filter cap, they can be a B sometimes. Sometimes a pair of water pump pliers works, sometimes a punch is needed. Try and stay away from the bottom side when using a punch, the cap sealing surface can deform. If that happens a file can be used to take the bump out. The pump body is aluminum, the cap is steel. If there has been H2o in the fuel the cap will rust and the aluminum blooms making it difficult to remove.

Matt, Diesel Creek. I love that channel!

 

[LCA078]

Thanks, Will. I'll be sure to take care when working the filter cap. I didn't know the PT body was aluminum- I'll be careful snugging up anything that touches it. The inlet is an elbow so good info on removing the damper to be able to look at the gear pump. And yeah, Diesel Creek is a great show!

 

[LCA078]

I pulled the dampener and intake fitting off and had Soldier B crank. Looks like the gear pump is not turning, right?

Cummins PT fuel pump on M923 with NHC 250

Looks like gear pump isn't moving when cranking

youtube.com

 

[WillWagner]

If that is you video, no it is not.

One of two things. Drive in the front has come apart, the drive flange is aluminum and keyed plus held in place with a 5/16 fine thread bolt. Or the gear pump shaft has sheared.

No matter, pump needs to come apart.

 

[LCA078]

I was afraid of that. Okay- I'll do the research on R&R of the fuel pump as I think it requires a special half moon wrench. It may be a bit before I can remove the pump as I'm out all next month but it doesn't look too bad as a project. Just need to figure out what to do with the pump once it's off the truck. Thanks for guidance so far... MTF

 

[LCA078]

I looked at Wes's video on removing the PT pump and decided I could take a swing at pulling off it quickly. Within an hour (including watching Wes's video) it was boxed and in back of my truck as I head back home. Thanks, Wes.

And yes, the front looks good- spins freely but the gear pump on the back doesn't. Didn't play with it too much as the House CDR was texting me when I would be coming home to help out with her duties...instead of me playing motor pool. MTF

 

[LCA078]

With the pump off and I'm researching rebuild options, what other things do I need to consider?

-Bumping up the HP would be nice as this is my "parade" M923 that's about to be singled out with 16.00s. I'm assuming a bump will help with bigger tires but have no idea what's a good bump without worrying about pyros, etc. What is a good bump up for this IP?

-Do I need to pull the injectors and send with the pump or just assume they're okay. I'm pretty certain contaminated fuel botched my IP so wondering if the injectors are affected.

Thoughts?

Edit: I understand there is no magic fix to add HP to the NHC 250 but I thought there was a few tweaks when rebuilding an IP to eek out a 10=20% increase... even it it can't be felt when driving. No need for turbos, dropping in a big cam, etc.- just simple stuff for a simple truck. I know ditching 16.00's and going back to the 11.00's will make a world of difference off the line but I want a softer (and cooler looking) ride with the 16.00s. Plus I need the 11.00s for another project.