2000 Cummins ISC 8.3L lift pump question

[Ncostello]

The ISC with the CAPS injection pump uses a lift or transfer pump much similar to the one on ISB engines in 98.5 to 2002 Dodge Ram trucks. It's a Carter basically and it's installed on a "head" block with inlets and outlets. I believe the return fuel runs through this block too.

This pump differs from the ISB in that it only runs for 30 seconds upon key-on, start up. After that the pump quits and the injection pump takes care of the fuel pulling duties. I think the unit I'm dealing with (on a fire truck) is on it's way out or has already checked out. It doesn't sound like it's under a load while running. It does move a little fuel because it worked for filling the new filter not long ago. But it took a lot longer than normal. The ISC fired up then died due to air in the system. That's never happened in 14 years on this truck's annual filter change. We usually run the pump for a minute (2 key on cycles) and all is good.

There was a TSB from Cummins to replace the top cover (in this case the pump to "head" block) gasket on this pump which I did. But it didn't really help that I can tell.

Cummins used to sell the replacement pump/motor. But now only sells the pump/motor with a new block assembly. This increases the price $300 and adds about 2 hours to the job.

If you take the typical Carter pump ISB owners use, remove the three stud screws on top, remove the top plate...and plug both the inlet and outlet you have what I have. These Carter pumps were left with the typical inlet/outlet holes undrilled. The inlet outlet function is handled by the "head" block the pump attaches to. Fuel comes in the top of the pump and exits the top of the pump.

Anyone know the PSI of this application? I may try a Dodge replacement pump (same connection even) and just remove the top plate. I'd have to buy some metric plug bolts and sealing washers to take the place of the banjo fittings. But other than that I bet it would work. The Dodge pumps run at 15psi but I have no idea on the CAPS ISC engines. I bet 15psi wouldn't hurt anything here if it doesn't hurt the VP44. And 15psi is better than my 0 psi now.

 

[Bob4x4]

You can buy a universal carter pump with either 7 or 15 psi from summit racing as well as other outlets. Be sure to get the hp version of either psi model for more flow. It will come with 3/8 not fittings -easier to plug

 

[mwilson]

We worked on another one earlier in the month, I think 5 psi min and 15 max. Service manual test procedures in the thread.

Thread here...

https://www.turbodieselregister.com/threads/250014-02-8-3-with-deceased-inj-pump?highlight=series

Mike.

 

[Ncostello]

Thank you for the information! I agree the 3/8" plug would be easier to deal with. I'll just make a pigtail harness with the correct Deutsch connector on one end and rings on the other. This will get me pumping correctly without all the hassle of removing the other hardware and paying the higher price, when only the pump/motor is the problem.

 

[Ncostello]

I bought a new Cummins lift pump assembly for the ISC 8.3L. As it turns out a typical Carter pump won't match up as the top side is machined a little differently as well besides the inlet/outlet differences.

The OEM lift pump setup is simple. Upon key-on the lift pump cycles on and runs for 30 seconds to push fuel to the filter and thus the injection pump. Even after engine start the electric pump continues to supply the injection pump with 15psi (or so) for the 30 second run time. After the 30 second time the Carter pump turns off and remains off. The CAPS injection pump has a gear pump that pulls it's own fuel. It takes over the fuel delivery duties on its own. The filter goes into a vacuum mode at that point as the Carter is off. There is a check valve in the lift pump assembly that allows fuel to be pulled around the now idle Carter lift pump.

The new lift pump assembly seemed to pump fuel upon installation. You could tell that after key-on (engine off) the pump bogged down and was really making some noise. I opened the schrader like valve on the injection pump and fuel was really coming out under pressure. I never started the engine. I cycled the lift pump again. This time it didn't want to pick up and pump fuel. It was free wheeling like it had lost prime and wouldn't pick it up. Then later it would pick up fuel and pump hard. No rhyme or reason as to when it would pump.

The suction fuel line is a solid single run. It's the heavy duty braided air brake line with steel flare fittings on the ends. There are no known leaks from the tank fitting to the lift pump. The fittings on both ends are tight and leak free. Yet this system seems like it will not hold a prime.

After the Carter pump turns off you can hear fuel "hissing" around inside the return lines for a second as the entire system pressures down from 15psi.

With the engine off, and the lift pump known to be under load pumping fuel, I removed the fuel return line going to the tank. Nothing. It's as if the lift pump is dead heading under load and fuel isn't going through the filter and injection pump then back to the tank (engine still off). This is how the Cummins manual says to prime the system. Cycle the pump several times.

But if nothing is ever returning to the tank during this time how could it be priming anything or purging air?

I started the truck and there were no issues. It started fine and ran fine under load for a couple hours. But as you shut if down, the whole system loses prime. I removed the pressure test ports on the lift pump assembly and there is no fuel down in there. If you remove the filter, the filter isn't even 3/4 full. Yet the truck runs and operates fine like this.

Shouldn't the fuel system, at least up to the injection pump inlet, always be full of fuel and held in prime all the time? If each time the truck is shut down and the system partially drains off I'm dealing with a bunch of air in the system every time it starts. Yet it seems to operate this way. This can't be right.

I'm about to rip the Carter assembly off and install a Cat pre-filter and hand primer pump setup. At least the system will be primed at all times and the injection can pull fuel on it's own 100% of the time.

Best I can tell the system is in good shape. The only wild card for me is the injection pump. I have little idea how it's supposed to be letting fuel through during priming, and if it's supposed to keep the system primed up with it's internal workings etc. It's like fuel can't get through during priming (no return to tank at all) and then when off it lets fuel prime (after it's been running) release.

 

[Ncostello]

"A lift pump is used for priming the pump at start up. The lift pump runs
for approximately 30 seconds after key-on. Once the engine is started,
the gear pump is able to maintain prime without any assistance from
the lift pump.

The gear pump supplies fuel to the pumping plungers through internal
drillings in the cam housing. The gear pump also supplies fuel to the
distributor for lubrication and injection line refill purposes. The gear
pump is regulated to approximately 180 psi at 2400 engine rpm. The
gear pump has an internal filter to catch any debris generated downstream
of the main, external fuel filter. The pump camshaft is driven off
the engine camshaft (just like the Bosch pump), therefore pump rpm is
one-half engine rpm."

The above is from a New Holland shop manual regarding the Cummins ISC fuel CAPS pump. From the sound of it, it sounds like every time the engine is started the electric pump helps the gear pump pick up a prime, then the gear pump keeps the prime. But what about start up? Is there enough fuel in the pump to start up even if the system loses prime? This is all strange to me.