Cummins ISC lift pump replacement

[dale1]

sequest7. I'm having similar problems. would like to know the outcome? thank you, dale

[jacwjames]

dale1
You should sent a PM to the person.



Just click on the name in the post and a drop down menu will pop up with one option "Send PM", click on it an it will bring up a text box to send message.

[CountryB]

Originally Posted by cewarre

I spoke with Carl at Capital Volvo, 1-800-247-5673 and he said he still has 370 of the aftermarket gaskets in stock for the Cummins lift pumps and gets calls quite often. They are still $6.71 each and he is shipping me two via UPS. He said the aftermarket gaskets reference to Cummins part numbers 3964385 and 4935004.

Did you confirm that the part numbers for the gasket is correct? The numbers you listed don't match what others are posting (i.e. gasket is 4928511).

Also what engines, if any, (besides the ISC) use this same transfer pump?

[Rcook1956]

Convert to a FASS pump and never have a problem again. Look them up on internet but best to give them a call. I converted mine to a 165 gph pump in a few hours.

[cbr46]

Originally Posted by CountryB

Did you confirm that the part numbers for the gasket is correct? The numbers you listed don't match what others are posting (i.e. gasket is 4928511).

Also what engines, if any, (besides the ISC) use this same transfer pump?

On my 2003 ISC (2002 motor?) the gasket is 3944382, and doesn't look anything like the gasket in the above thumbnail.

- bob

[BMU-Scotty]

I think all RVs came with an earlier model engine. I.e., a 2003RV probably has a 2002 Cummins engine.

As for the Cummins OEM (Carter) Lift Pump and fuel delivery system, which sucks, literally Cummins does not like talking about their lift pump very much or how it works; or if there is even a check valve installed as shown in the diagram. It's all a big mystery; and getting technical support is hard... from anyone.

This is because today's technical support team(s) barely understands how a CAPS-1 or CAPS-2 (aka HPCR used in 2005-6 RV) fuel system works. However, you can't blame them since they stopped delivering these systems back in 2003/4 and none of these guys have ever replaced a CAPS pump and those techs who have probably forgot how these things work. ...For that you need to talk to a Farmer who is still running ISC motors made back then.

On the positive side, I will say the Cummins telephone technical support is very helpful, and far more likely to help you vs. the customer service you will get by taking your RV to a Cummins Stealer.

As to the gasket part number and type: From 2001-2004 each RV sold with a Cummins ISC/ISL OEM lift pump came with it's own gasket part number; and I think this is because, IMO, as these lift pump gaskets continued to fail due to USLD fuel changes; so Cummins kept making new gasket materials, which explains all the different part numbers, even though the OEM lift pump looks the same.

You see, the older gasket with a screen was supposed to be the fist line of defense against algae, and then the single 20u filter would do the rest.

But when the injection pump accumulator started to fail due to algae contamination, they started coming out with 2-filter systems (an upgrade) and some RV manufactures modified the fuel delivery system and shipped their coaches with a 20u-primary and a 10-u secondary filter.

Note: With a Cummins suction fuel delivery system you never want to install less than a 10-micron fuel filter. However, after you convert to a FASS or AirDog you can run 2 filters. I recommend the first filter being 20u or larger (not smaller) and the second filter can be as low a 3u. I also prefer FASS because I like their high rate of fuel flow back to the fuel tank, which means you a lot of fuel 100GPH will be filtered as you drive. And that will take care of most algae concerns over time. They call it "fuel polishing." Whatever.

Moving on: Winnebago was too cheap to install 2 filters so most of their RVs only came from the factory with 1-10u filter; leaving owners to upgrade to 2-filters, which was better after they started have performance problems, commonly due to algae. (This why you need to use a biocide when you store your RV for more than 3 months.)

Moving on: The CAPS gear-driven fuel pump (not to be confused with the 30-second lift pump, which is used to prime the engine for starting purposes only) is based on -15psi of suction. And when that lift pump gasket starts to leak/suck air, usually because those 3-lift pump bolts are loose, or the gasket material is disolved by modern day USLD fuel, what happens is that the suction is lost... and that's the root cause of all these CAPS injection pumps failing. I.e., the fuel provide the cooling and when you starve your CAPS injection pump of fuel, it heats up, and all sorts of bad things follow.

Example: You may think you lost a suppressor diode, but most likely the real problem is propagated by not enough fuel. And the root cause is this: Your OEM gear pump (-15PSI) is not able to overcome pressure decreases (climbing hills or having less than 1/4 tank of fuel to begin with); and on top of all this, your new ULSD fuel does not contain enough Sulphur in it, like it used to, to lubricantes the CAPS injection pump.

...Then the stator starts working overtime, and the suppressor diode can't block the transients shock which protect the ECM.

...Then you break down, get your RV towed, your trip is ruined, and the Cummins Stealer Shop wants big money to replace the ECM, or worse, both the ECM and the CAPS injection pump ($8,000+). It's a racket. And all because you didn't what you now know!

So what can you do? Answer: Install a FASS or Airdog, and which type may depend on which method is easiest and cheapest to install for your type of RV chassis. I.e., it all comes down to the best/easiest/cheapest way to run a new electric lift pump fuel return line.

Note: Bothe FASS and Airdog will turn your OEM (suction type) fuel delivery system in to a positive (+15PSI) delivery system.

Personally, I have no preference. FASS vs. Airdog, but the easiest installation will mostly depend on it you have easy access to route a new fuel pump return line to your tank. If so, I would go with FASS. If not, I would go with AirDog.

To recap: If you don't have a FASS or Airdog. And I would say, you should get one ASAP if you plan on driving your RV a lot, but cause your chance of experiencing a CAPS failure increases over time; and by time I mean 50K+ miles. I.e., if your rig is at 50K miles or more, and who's isn't these days, and you have not installed a FASS or Airdog, then you really should think about it.

====

Regarding the lift pump "manifold." This thing is cast pot metal. And the fuel line-in ports are separate from the CAPS fuel return that sends fuel back to the gas tank. So when you talk about the air entering the system you are only dealing with the gasket that goes between the fuel pump manifold and the OEM lift pump that runs for 30 seconds. And the fuel return ports inside the Lift Pump Manifold are totally separate and have nothing to do with that lift pump gasket leaking air or leaking fuel on the ground.

Remember: The general concern is that all fuel coming from the fuel tank is being sucked by the CAPS gear driven fuel pump; and that 30-second lift pump is turned off after the engine starts. However, fuel is still passing through the fuel-in ports of that lift pump manifold. So even though the 30-second lift pump is not a factor after the engine starts, that lift pump gasket can let air get sucked-in.

Therefore, if you are experiencing "issues" with your engine performance, or if on cold days your engine starts and then stops; or if your engine starts and then stops when you lave less than 1/4 of fuel... Step-1 is to tighten those 3 lift pump bolts and see if that fixes your problem.

Step-2, which I highly recommend, is to install a FASS or Airdog -- and preferably bypass the lift pump manifold fuel-in port as much as you can.

To accomplish this, some people plug those lift pump "manifold" ports, while other owners just remove the primary filter and put a FASS pump in it's place and run 3 filters.

IMO, there is no need to have 3 filters as show in the diagrams above. In fact, the more you can do to simplify your fuel delivery system the better. And this included bypassing your lift pump all together.

Once you provide "+" fuel pressure to your CAPS injection pump, by installing a FASS or Airdog electric lift pump, you know you will get sufficient fuel flow and marginal cooling.

That said, I also recommend you always supplement your diesel fuel tank with a diesel additive at each or every other fill up, because your CAPS injection pump needs as much lubrication as it can get -- that is if you expect it to last forever, which it will do, if you take care if your fuel. And if you don't install a FASS or Airdog, then you maybe driving on "borrowed time."

[dons2346]

"...Then the stator starts working overtime, and the suppressor diode can't block the transients shock which protect the ECM."

Scotty, you are the first to mention the diode, congratulations..


I actually had a diode go south on me and the Cummins stealer was talking lift pump and an array of other parts. Luckily I have a friend that is a certified Cummins guy and after giving him the codes, he said suppressor diode which was a $127 part. Much better than the big buck pumps,

[cbr46]

Originally Posted by BMU-Scotty

I think all RVs came with an earlier model engine. I.e., a 2003RV probably has a 2002 Cummins engine.

As for the Cummins OEM (Carter) Lift Pump and fuel delivery system, which sucks, . . . .

That is and EXCELLENT "prim-er"!

I didn't know about the suppressor diode. My main concern was sucking air into the fuel from a leaky lift pump. Now I'm curious how the suppressor diode works . . . .

In my case the gasket holes wouldn't even line up with the holes in the lift pump. Yes, probably a 2002 engine. Now that the leak was much worse I ended up bypassing the lift pump.

And yes, I installed a FASS pump for many of the above reasons.

- bob

[mydogmax]

So if you have a model newer then a 2004, your pump should be ok?


Where is the assist pump normally mounted?

[cbr46]

Originally Posted by mydogmax

So if you have a model newer then a 2004, your pump should be ok?

Where is the assist pump normally mounted?

After 2004 Cummins switched from the CAPS to HPCR fuel injection pumps with the same lift pump to prime it. Fuel is still sucked by a multi-thousand dollar pump from the main tank 20 feet away, not a great design. Maybe it's the fear of failure like the CAPS pump I don't know.

The "assist" pump (FASS or Air Dog) is mounted wherever the installer can or wants. Some like it near the source (fuel tank) so it's mostly pushing fuel, some like it in the easiest mounting location . . . . like the primary filter location (replacing that filter). The FASS has 2 filters mounted to it - a 140 um primary with a 2 um secondary filter. This makes the ISC 10 um secondary filter rather useless but most everyone leaves it in place.

HIGHLY RECOMMEND installing a fuel gauge with sensor at the secondary filter so the driver can see pressure falling as the FASS (or Air Dog) filter becomes clogged with particulate or water. The FASS filter does NOT have a water drain. Also HIGHLY RECOMMEND using a fuel treatment such as Biobor JF to add lubricity to the ULSD (Ultra Low Sulfur Diesel) fuel during fillups . . . and it kills algae that may develop if the coach has infrequent use. A few pennies spent on fuel can save thousands if the CAPS or HPCR pump fails (not to mention towing, overnight costs, transportation home & back, downtime, etc).

- bob

[macktruck345]

I’ve installed a Fass pump near my fuel tank. Now my transfer pump is leaking. I suspect because of the 16lbs of positive pressure. Can you tell me the best/easiest way to bypass the transfer pump? Could you reply to macktruck345@gmail.com please? Thank you so much!!

[mackwrench]

Originally Posted by macktruck345

I’ve installed a Fass pump near my fuel tank. Now my transfer pump is leaking. I suspect because of the 16lbs of positive pressure. Can you tell me the best/easiest way to bypass the transfer pump? Could you reply to macktruck345@gmail.com please? Thank you so much!!

Mack-
I installed the pump after the OEM lift pump. The lift pump ain't designed to be pressurized.

You should be able to make a line to run from fass pump to OEM secondary filter. The return will still use the lift pump manifold.

[jacwjames]

I bypassed the transfer pump by removing the two fuel lines and putting a union in https://www.ebay.com/itm/401701970586 , then just capped the transfer pump https://www.ebay.com/itm/163195337791 .

[cbr46]

Originally Posted by jacwjames

I bypassed the transfer pump by removing the two fuel lines and putting a union in https://www.ebay.com/itm/401701970586 , then just capped the transfer pump https://www.ebay.com/itm/163195337791 .

Same here. It was the easiest solution.

- bob