M939 Quick Fuel Filter and Pump Re-Prime After Changing Cartridge Element

[74M35A2]

So how does one refill the large cartridge fuel filter container after changing its filter, reassembling it dry, and therefore losing the prime charge on the mechanical lift pump? After nearly killing my batteries, and going through a full can of starting fluid, I realized just cranking and short run bursts was not going to do it. I disconnected the fuel line connection at the lift pump (A2, Cummins 6CTA8.3 engine). Then, applied a vacuum pump with liquid trap (small glass jar) on this suction line. 15 seconds later, and ah-ha! Diesel is present all the way to the lift pump now, and the engine fired right up. I was going to blow compressed air into the fuel tank, but after seeing 4 connection ports, and figuring 2 were vents, I did not feel like closing all of these off, and went another path. I did not have any clean diesel fuel handy in a pour type can to refill the canister. Hope this helps, and apologies if it was already posted.

 

[Floridianson]

Yea my friends have a Medical background and they have two vacuum pumps like that. I'm thinking since they don't use or need them anymore Merry Christmas too Me.

 

[mcmullag]

There is a 'pump' on the side of the drivers side engine block area near the secondary filter.
There is a 10mm bleed screw on the injection pump near the front of it between the pump and the engine block.
Crack open the bleed screw with a 10mm wrench and use your thumb on the 'pump' thing. would be best if you have two people to do this.

 

[74M35A2]

Thanks

I didn't know about the bleed screw, thanks. I need to do more reading. I was depressing the hand plunger on the side of the engine block, but it felt like no resistance at all beside the return spring within it, and with nowhere for the outlet of that pump to relieve at (bleed screw as you mentioned), it wasn't doing anything. Plus, that is a large canister to fill with a small hand pump. In the field, absolutely, this should work with some time. Thanks for the tip.

The vacuum pump worked in 15-20 seconds, though not everybody has access to one. I have this vacuum pump for HVAC work, and also to change the oil in my boat (sucked up through dipstick).

 

[paulrance]

Where is the big fuel filter at? I found the one that's on back driver side of block, plus the inline one. Is there a main big fuel filter? Wish my truck was close id go look.

 

[74M35A2]

I'm not sure which one you are referring to about "the inline one". On my 1991 M925A2 (Cummins 6CTA8.3 engine), there is a large frame mounted filter/separator located just behind the front driver side tire. This unit is no smaller than a 10+ cup coffee pot. It is mounted on the outside of the frame rail. This is a cartridge type canister filer element. Then, there is a much smaller engine mounted spin on filter/separator on the driver side, rear upper portion of the engine. This filter is smaller than an automotive oil filter.

I am unsure of any other MV filter configuration. Even the Cummins NHC-250 engine M939 series trucks may be different.

 

[todds112]

This thread just saved me. I drained a little fuel out of filter per PMCS. Truck ran for a while then died and wouldn't re-start. I figured it was air in the system and went to the TM. They say to prime the system, but both version I have only showed the older style pump with the "T" handle and a bleed valve right on the pump. I looked everywhere on my 8.3 and didn't see anything that looked like a bleed valve. I found this thread and was able to locate the bleed screw on the IP. After opening it and pumping the primer about 20 times, fuel came out with no air. Truck started right up! Thank-you, thank-you!

 

[MtnSnow]

Todd and others with the 8.3 there is also a bleed screw just up and behind the engine mounted fuel filter towards the firewall. I mention this one as sometimes it can be a pain to use the one on the IP..

 

[M35A2-AZ]

The bleed screw on the 8.3 is on the back side of the pump. It takes a 10mm wrench.
Just stand on the tire on look over on the back side of the injection pump and you will see it.

 

[Andrmorr]

So how does one refill the large cartridge fuel filter container after changing its filter, reassembling it dry, and therefore losing the prime charge on the mechanical lift pump?

You can get a 24v inline fuel pump made by FACET (high quality pump used on military generators) for about $50 on E_ay. It is self priming, small(about the size of a baseball) only 5psi and can be plumbed in a parallel line to your fuel line with a check valve at each end. If/when you need to prime your fuel lines, turn on the pump, it primes itself then PUSHES fuel thru your lines to your engine...this will also prevent the common problem of pinholes in fuel lines causing a NO START situation by leaking air and preventing fuel from being pulled into engine (can also use pump to create positive pressure in lines and find leaks)... Trucks with 2 tanks can also use this type pump to transfer fuel from one tank to the other and bypass the problematic tank selector switch. AND, if you're real creative you could add a quick attach point at the pump that would let you use a hose and the pump to transfer fuel from your truck tank to your tractor or an "Out of fuel" buddy's truck...

Search 24v facet pump...

Voltage: 24v
Part & Cross Reference Numbers: Facet 40164N, 40164E, Case L60822, Caterpillar 9S7784, National Military 2910012105733
Features: Compatible - with Leaded or Unleaded Gasoline, Diesel Fuel, Blended Fuels, Pure Alcohol & Fuel Additives. Reliable - No Electrical Contacts, Bearings, Rubber Diaphragms or Valves to Wear Out or Fatigue. Easy to Install & Service. Eliminates Vapor Lock - for Constant, Smooth Fuel Delivery on Hot Days & High Altitudes. Pressure Relief - Eliminates Flooding & Assures Satisfactory Restarting on the Hottest Days. Corrosion Resistant - the All Steel Case Is Plated to Provide Over 100 Hours of Salt Spray Resistance. Self-Priming - to 12 Inches of Fuel Lift.

Filter Specifications: N/A
Fitting Type: 1/8-27 Internally Threaded
GPH: 32
Min Dry Lift: 12in / 30.48cm
Max Shutoff Pressure: 6 PSI
Min Shutoff Pressure: 4.5 PSI
Negative Leads: 0.25" Ring Terminal
Includes Positive Shutoff Valve?: No
Includes Check Valve?: No
Includes Quiet Valve?: No
Packaging: Box
Application: All Carburetor-Equipped Cars, Vans & Light Trucks, Stationary Engines, Gen-Sets, Fuel Priming & Transfer Applications
Weight: 1.07 lbs / 0.49 kg

 

[highfavor1004]

Thanks for this thread. I have been researching all morning. My Buddy asked me to help him change his fuel filter in his M923 8.3 cummings today. I was try to educate my self before helping him. There was not a hole lot of information out there on the military 8.3 version. I am used to working on M35 and have not fooled around with the 900s. I know that the deuce has three fuel filters. The water separator, and the two Primary. How many does the 8.3 have in the M923? I have found a few picture but nothing on a military version of the motor. I am sorry for asking such an elementary question, just have never messed with 8.3 before and want to help my buddy as much as possible. I have been trying to find the correct TM for the Fuel system on 8.3, but it keeps coming up as a 250 cummings. Thank you.

 

[trooper632]

My 923a2 just started where it wont stay running, after about 90 seconds. I loosen the 10mm bleed screw and prime it until straight fuel comes out tighten screw and it fires back up just to die again after about 60-90 seconds. Have gone thru this procedure about 15 times, tired of looking at the **** thing. Even filled up large filter canister. Really don't want to replace all the fuel lines, was hoping it just wasn't primed all the way, Guess its gonna sit another 2 months.

 

[therooster2001]

Thanks for this thread. I have been researching all morning. My Buddy asked me to help him change his fuel filter in his M923 8.3 cummings today.

You found the right help in this thread. Check the picture above in post 8, the orange filter is one of the fuel filters on all of them, the next one will either be a small inline filter right below the lift pump (follow the line) or the big mounted one right by the fender (it's huge), that's the water separator. Technically so is the orange one. My truck did not have the big separator, and I missed the little filter originally. Easy. Check the 5-ton part spreadsheet in the main 5-ton forum for the different filters / NAPA parts numbers.

 

[MtnSnow]

My 923a2 just started where it wont stay running, after about 90 seconds. I loosen the 10mm bleed screw and prime it until straight fuel comes out tighten screw and it fires back up just to die again after about 60-90 seconds. Have gone thru this procedure about 15 times, tired of looking at the **** thing. Even filled up large filter canister. Really don't want to replace all the fuel lines, was hoping it just wasn't primed all the way, Guess its gonna sit another 2 months.

With you saying it keeps quitting on you I would say you have a bad fuel line from the tank to lift pump. Depending on how your 8.3 motor is configured the hose from the tank to the IP maybe a 1 or 2 pieces of rubber along with some hard line (copper) which actually introduces several more joints that can leak air. You can replace all of the line from the tank to the lift pump with rubber lines for under 30 dollars.

 

[Jayco36REQS]

Ok, so how the heck do you remove the PT Pump Fuel Filter bolt? On my pump it's a big slotted bolt (not a hex bolt). I've tried scraping away the factory paint around the edges, a big screw driver, and a wrench on the screwdriver... Won't budge!


Help!!!

 

[Jayco36REQS]

Got it... made my own tool out of a piece of an old file and welded a handle on it... quick tap of a hammer and it loosened up without slipping..

 

[georgie c]

thanks for the info I just ran my M923 A2 dry. the lyin fuel gage says a quarter tank . I loosened the bleeder behind the ip and worked the pumpie thingie furiously closed the bleed and it started rite up

 

[simp5782]

thanks for the info I just ran my M923 A2 dry. the lyin fuel gage says a quarter tank . I loosened the bleeder behind the ip and worked the pumpie thingie furiously closed the bleed and it started rite up

Never trust any MV fuel gauge. Always look into the tank. They are known to be dedicated liars. After you have your MV a while will know when you need diesel.

 

[georgie c]

I had just driven her home from eastern supply in Philly pa. through pre-memorial day traffic . pulled around behind my house and she ran out of fuel. great timing for once

 

[Grond]

Todd and others with the 8.3 there is also a bleed screw just up and behind the engine mounted fuel filter towards the firewall. I mention this one as sometimes it can be a pain to use the one on the IP..
View attachment 557513

its the primer assembly there Oem or after market? it looks different then the one in mine and it is in poor condition and in need of replacing part number? 8.3 M934