Replace Cummins PT fuel pump

Here is some info for anyone faced with this task. First of all, the purpose of the Cummins PT pump is to draw diesel from the fuel tank, and raise the pressure in proportion to throttle input, and send the higher pressure fuel to the injectors, where it is further pressurized for injection. If the pump is not working well, hard starting, low power and other issues can result.

In my case, the pump is equipped with an aneroid valve, which further adjusts fuel pressure based on turbocharger boost. If this valve is not working, the pump will never produce full pressure, and the engine will have low power.

I suspected my aneroid valve was bad, thanks to input from reb87 and others on this site. So I got busy and pulled the pump and sent it for rebuild. The task is simplified if you remove the fender, a simple 6 bolt task in my case (M915). To access the pump rear lower mounting bolt, I had to remove the power steering pump, a simple 2 bolt removal. The real trick to pulling the pump is the upper rear mounting bolt. This requires a 12 point, 7/16 swivel socket, such as a Proto 5274 (see pic). The rest of the task is very straightforward.

BTW, yes, the aneroid valve was bad, making my fire breathing Big Cam 400 perform like a wimpy 250. That problem is now behind me . . .

NDT said:

Here is some info for anyone faced with this task. First of all, the purpose of the Cummins PT pump is to draw diesel from the fuel tank, and raise the pressure in proportion to throttle input, and send the higher pressure fuel to the injectors, where it is further pressurized for injection. If the pump is not working well, hard starting, low power and other issues can result.

In my case, the pump is equipped with an aneroid valve, which further adjusts fuel pressure based on turbocharger boost. If this valve is not working, the pump will never produce full pressure, and the engine will have low power.

I suspected my aneroid valve was bad, thanks to input from reb87 and others on this site. So I got busy and pulled the pump and sent it for rebuild. The task is simplified if you remove the fender, a simple 6 bolt task in my case (M915). To access the pump rear lower mounting bolt, I had to remove the power steering pump, a simple 2 bolt removal. The real trick to pulling the pump is the upper rear mounting bolt. This requires a 12 point, 7/16 swivel socket, such as a Proto 5274 (see pic). The rest of the task is very straightforward.

BTW, yes, the aneroid valve was bad, making my fire breathing Big Cam 400 perform like a wimpy 250. That problem is now behind me . . .

Click to expand...

OOOOOhhhhhh Big Cam 400...
how do you like it??? there is a b/c 350 in the corner of my shop i have been thinking of in-framing and tossing it to my m813..

Just a note : in your third picture .....
Most tech's just remove the 12 volt solenoid and fuel shut off from the pump " couple of screws and two square o rings" to get to that bolt. It will not change any fuel settings and make you life so much better when trying to get that darn bolt in or out. just seal the holes off with tape to make sure dirt does not get in the pump when your installing it.

Thanks for the info!!!


Vinny

Did your tec raise the pressure?

Cummins PT Pump

I have a 1983 AM General M931 5 ton with the 250NHC Cummins! I am having injector pump problems. It is leaking. I have to use the hand primer to prime the pump each time I crank the truck. Plus I have low power from the truck. I have found a pump on ebay that MAY be correct but I'm not sure.
531-4567A279438???????
http://www.ebay.com/itm/301401975150?_trksid=p2060353.m1438.l2649&ssPageName=STRK:MEBIDX:IT
Thanks

I will bump this since I just had an issue with an aneroid valve on the BCIII i put in my 923. I had my pump rebuilt and they went thru it and said the aneroid valve checked out just fine. so they lapped it and put it back together with the rebuild.

Put the pump on the NTC400 and hooked all the lines back up. The 4 lines going to the pump. AFC vent, Aneroid Line, Fuel feed line and the return on the rear gear pump. When she caught fuel she ran wide open to the governor. I mean just deafing when you are sitting next to it. Shut it down. checked all the lines. Cracked the manual shut off valve and when she started she ran up to 1100rpms and i made sure the throttle was closed and shut the shut off valve again. Figured it had to be the pump so i put the small cam pump on and hooked it all up and everything was fine. engine ran good. Took the pump back to the shop and bench tested it and it came back fine with 240 RP. They did not have anything hooked to that aneroid line. They said it was the motor back feeding fuel but the only difference between it and the NHC250 pump was that aneroid line.

So i had them put the aneroid block off in the pump so that I only have the dual feed lines coming out the top and the return on the rear of the pump. Put the pump back on and it fired off as it should.

So an aneroid valve can cause a WOT run away situation, as well as the lack of power, since it was basically bypassing fuel right back into the pump just below the fuel solenoid and giving the engine all the fuel it wanted. i talked to will this morning and he was in agreement to block the thing off as well.

I'm confused. The engine won't run right with the pump that came on it if connected as designed? You have to deliberately leave something off in order to have proper fuel control? If so, something is not right. Either your shop screwed something up, or you have something not right.

74M35A2 said:

I'm confused. The engine won't run right with the pump that came on it if connected as designed? You have to deliberately leave something off in order to have proper fuel control? If so, something is not right. Either your shop screwed something up, or you have something not right.

Click to expand...

You don't need an aneroid valve anyway it is just emissions. It can get stuck closed like in NDT's case and limited his power or hang wide open. It is a slide plunger that responds to pressure. It was allowing fuel to bypass. My NHC250 had it blocked off from the get go when i had it rebuilt. Everything was hooked up accordingly as to how it goes on three trucks. So it might have been the internals of the aneroid even though it was bench testing fine without being hooked up it just wouldn't work on the truck right with actual pressure to it. pictures shown. The aneroid and return share a return line from the fuel return. On towards the back of the head there is another T that allows fuel to return to the tank on that same line.

compared to the pump after the block off and with how the NHC250s are setup.

The first pic with the arrow pointing at a line is NOT an anneroid, that is the hydraulic ASA line. IIRC, there is a check ball in there and the fitting is orificed. It is a noise emission device. All it is there for is to quell the "marble rattling" noise on acceleration on a rolling start, like if you were rounding a corner and accelerated. The anneroid would control the smoke, that valve controls the noise you engine makes. Yes, it was a Ca EPA deal. Guess Ca had snowflkes back in the 80's too!

Should I delete(cut lines)both anneroid valve and EPA sound thing and how do I do ? What's the pros n cons.thank u