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Old 11-11-2022, 08:14 PM   #1
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Lift pump toast?

This happened to my Cummins 8.3L ISC 350 engine. Please share what you think...

The first time it happened was about a month ago when I drove from Palm Springs to Menifee there was a moment of lost power on a local road I thought it was transmission fluid low, so upon arrival I parked and checked the fluid level the shift pad said OK. After sitting for 21 days, in the morning of exit I started up engine and felt it was idling unstable. Once I drove out of the park the engine choked but I was able to move to the side of the road.

Twisted open the water separater on the primary filter, I noticed some black granules in the fuel out, I knew it's microbes/algae. The diesel was last filled at Costco in Bakersfield in Sept ("biomass" as it labeled, I knew it could get me in trouble along with the temperature drops). Luckily I had filters in hands, so first I replaced them, and continued the trip towards a park in San Diego.

Next 80 miles was uneventful. But just about 10 miles to the park, the engine was stopped twice while waiting for green lights. Re-started it and made to the park.

Unable to get Biobor Jr locally but found Bio Kleen (made by PS Services), poured it into the tank, and filled with 2 gallons of fresh diesel afterwards. After 2 days' sitting I gave it a test yesterday, engine was up but ran for 5 minutes or so and stopped. It cranks but no start since.

This morning I went to Cummins and grabbed a set of new filters. Afternoon I removed the primary filter, but was surprised that the filter was only half full with fuel. I thought it should had been full to the neck. Now I am thinking if the lift pump failed.

Your thoughts? Appreciate any inputs.
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Old 11-11-2022, 08:54 PM   #2
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The Cummins CAPS lift pump is only powered for 30-45 seconds when the ignition is first turned to the run position. After that the main injector pump pulls fuel from the fuel tank, through the filters.
Now if the lift pump gasket leaks(bio-diesel is IMO the cause) which is common with older Cummins ISC and ISL engines, it will suck air into the fuel system. Then when the engine is stopped fuel will leak out, resulting in the main pump losing prime. Your description certainly sounds like this is what is happening.
The first action is to tighten the 3 bolts holding the lift pump to the 12V motor. If that doesn't stop the leak, the next step is to replace said gasket. There are 2 styles of this gasket.
I was on the road in 2020 when this happened to my engine. Cummins shop replaced my lift pump @ $5,000 final bill.


When you turn on the key to run, wait that 30-45 seconds before starting the engine so the lift pump can fill the fuel system and the main pump does not lose its prime.
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Old 11-11-2022, 10:26 PM   #3
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Thanks Ray. Yes the lift pump was leaking fuel on my last trip, I tightened the three bolts and no longer leaking. I did notice that the pump low pitch noise used to be much louder when it was running, now it is merely audible.

Sorry Ray you paid big bucks to replace the pump . It happens especially when no other options available at the time of needing it the most. I asked the local Cummins about the pump while I was there today. They had the pump in stock for $523 apiece.

I'll tighten the bolts a little more and see if the engine starts up. Worst case scenario I will replace the pump...
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Old 11-11-2022, 10:37 PM   #4
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Steve,, did you keep the old filters? It would be interesting to cut them open to see the contents. Granules, to me sounds like fuel line coming apart. Did you feel them to see if they were hard or could you squeeze them flat?


Do you see any leaks around the lift pump? Just read you post. You can buy just the gasket if you think it is leaking and if you decide to change the pump, I think you can beat that price. Cummins is real proud of their parts.
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Old 11-11-2022, 10:49 PM   #5
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Steven, I believe the latest primer pump from Cummins for your ISC/CAPS has a much higher pressure that the original, so it may be worth the $$$.
I thought I had the spec pdf but appear to have lost it in a data transfer from a failed hard drive.

I didn't lose this though.
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Old 11-12-2022, 07:38 AM   #6
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If you look in Quickserve you will find the procedure for testing the lift pump pressure. The lift pump on the 2003 ISC CAPS I owned had a plug on the top of the lift pump that could be removed and you can put a gauge on it. It has another plug to measure vacuum. Cummins calls them M10 Storm fittings but they are just 10mm X 1.0 threads which can be adapted to 1/8" NPT using this Equus kit found at any auto parts https://www.iequus.com/9848.html

Block Mounted Lift Pump
A malfunctioning electric fuel lift pump can cause slow engine starts or may result in an engine failing to start. The fuel lift pump can be cleaned and repaired to a limited extent. The lift pump will operate for 30 to 60 seconds
when the key is switched ON. The lift pump will also operate while the engine is cranking. The lift pump is contained in an assembly that includes fuel supply and drain manifolds. These manifolds provide for OEM connection of fuel supply and return hoses. The fuel supply manifold also contains M10 STORM fittings which allow for pressure and vacuum measurement of the fuel supply at the electric lift pump. A bypass check valve in the fuel supply manifold ensures that the system is primed by the lift pump. This check valve opens under vacuum created by the fuel injection pump once the engine is started. High vacuum measured between the electric lift pump and the fuel filter may indicate that this check valve has become plugged.
The output of the fuel lift pump can be checked through the following test:
Measure the output pressure using a pressure gauge at the lift pump outlet port.
The lift pump check valve restriction can be determined using the following test:
Install a 0 to 762 mm Hg [0 to 30 in Hg] vacuum gauge at the inlet and outlet M10 STORM ports on the electric lift pump head
Operate the engine at rated power condition
Record the inlet restriction at the inlet and outlet of the lift pump.
Refer to Procedure 006-020.
Maximum Fuel Lift Pump Inlet Restriction: 102 mm-hg 4 in-hg

From another thread: We went through two lift pumps before we figured out the lift pump hoses were breaking down. These are the hoses between the rear bulk head near the rear axle and the lift pump. Maybe 8 to 12 feet.
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Old 11-12-2022, 08:16 AM   #7
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Quote:
Originally Posted by CountryFit View Post
Thanks Ray. Yes the lift pump was leaking fuel on my last trip, I tightened the three bolts and no longer leaking. I did notice that the pump low pitch noise used to be much louder when it was running, now it is merely audible.

Sorry Ray you paid big bucks to replace the pump . It happens especially when no other options available at the time of needing it the most. I asked the local Cummins about the pump while I was there today. They had the pump in stock for $523 apiece.

I'll tighten the bolts a little more and see if the engine starts up. Worst case scenario I will replace the pump...

The price you quote here is for the Lift Pump, the price Ray quoted was for the CAPS injection pump.


Your lift pump had probably been leaking for a while before you actually saw it. Since it only runs for ~30 seconds to prime the CAPS pump it would take a while to see unless you actively look for it. After the engine starts then the CAPS pump takes over and it pulling fuel through the lift pump AND if it had been leaking it was pulling air. This is what eventually kills the CAPS pump and the +$5K bill that Ray mentioned.

Now if you caught your leak early and got it stopped the CAPS pump may be OK. But you have to confirm that your lift pump is actually working and priming the system.

I'd suggest loosening the primary filter and turning you key on and see if it pushes fuel out the top of the filter. You may have to cycle the key ~5 times to get it to do this. If you see fuel tighten the primary filter and then do the same with the secondary. If you see fuel tighten that filter, cycle the key 5 more times and then try to start.

If it starts and run you MAY be OK if the lift pump had not been leaking long. If it doesn't start and run I'd start looking at the CAPS pump.





I knew of the potential for my lift pump leaking and kept a close eye on it, checking often. In late 2020 after doing a service on my rig I drove and filled it up and then decided to clean my jacks. Crawled under the rig and YIKES!!!! I saw fuel dripping onto the lower exhaust (never hitting the ground). So after thinking about it I decided to abandon the lift pump and install a FASS transfer pump in early 2021. This pump runs continually and shows ~15psi at my secondary filter, this is the pressure the CAPS pump is seeing while rolling down the road. I've put ~12K miles on since.
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Old 11-12-2022, 09:50 AM   #8
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Big thanks to you all!! Your info is invalueable to me, and right to my thirsty brain!
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Old 11-12-2022, 09:54 AM   #9
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Steve,, did you keep the old filters?
Don, at the time I forgot about cutting them off to check the contents so they went to the dumpster.

I bought a gasket for it 5 years ago, from a Volvo dealer in LA, and replaced it. It did pretty good for so many years but I did see fuel on the ground at the check in gate from my rig. I think it keeps losing the tightness because of the aluminum housing that the threads are easy to be slipped. I'll check the fuel lines I hadn't thought about.
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Old 11-12-2022, 09:59 AM   #10
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Steven, I believe the latest primer pump from Cummins for your ISC/CAPS has a much higher pressure that the original, so it may be worth the $$$.
I thought I had the spec pdf but appear to have lost it in a data transfer from a failed hard drive.

I didn't lose this though.
Good to know the updated version has a higher pressure. Actually I did ask the Cummins counter guy about the differences between the old vs new, he told me he didn't know. . Yep the arrows you made on the photo are spot on.
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Old 11-12-2022, 10:03 AM   #11
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Good to know the updated version has a higher pressure. Actually I did ask the Cummins counter guy about the differences between the old vs new, he told me he didn't know. . Yep the arrows you made on the photo are spot on.
Steven; if memory serves ... and it sometimes does; the picture was one you posted a number of years ago before you replaced the gasket.
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Old 11-12-2022, 10:04 AM   #12
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Quote:
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If you look in Quickserve you will find the procedure for testing the lift pump pressure...
The test procedure sounds a good way to go. The fundamental always helps dive into deep. Appreciate the info!
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Old 11-12-2022, 10:13 AM   #13
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Originally Posted by jacwjames View Post
I'd suggest loosening the primary filter and turning you key on and see if it pushes fuel out the top of the filter. You may have to cycle the key ~5 times to get it to do this. If you see fuel tighten the primary filter and then do the same with the secondary. If you see fuel tighten that filter, cycle the key 5 more times and then try to start.

If it starts and run you MAY be OK if the lift pump had not been leaking long. If it doesn't start and run I'd start looking at the CAPS pump.
Jim, you are hitting the nail on the head. I am going to tighten up the bolts and test the fuel delivery to the filters. Hopefully the issue is on lift pump, not on CAPS pump.

I have heard of a lot good things about FASS pump. Certainly worth looking at it down the road.
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Old 11-12-2022, 10:15 AM   #14
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Steven; if memory serves ... and it sometimes does; the picture was one you posted a number of years ago before you replaced the gasket.
Ha, you found it but I forgot it... My memory is fading, not yours!
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