Leaking Lift Pump

Topic: Leaking Lift Pump (Read 808 times) previous topic - next topic

Leaking Lift Pump

December 05, 2021, 08:07:04 am

Ladies and gentlemen,

We are currently in Texarkana headed for an Appointment at MOT tomorrow morning.

When we started out yesterday morning at Lake of the Ozarks SP, I noticed a small leak (fuel dripping from the bottom of the lift pump). There was a 6 inch spot on the ground and the crossbar was also wet. Engine started and was running fine. Did not notice the leak until after I started the coach, so don't know if it is leaking when not running (we were there for 3 days). I decided to see if the coach could be driven. Perhaps I could make it to MOT or at least drive to a service center and avoid a tow or road side service.

Coach drove fine at low RPM. I stopped on the way out of the park to dump and fill the fresh water tank. I left the engine running and the leak was minimal. Maybe a drop or two every minute. The spot on the ground was about 3" when I left each of the two locations after 5-10 minutes at each place.

Decided to press on for Nac. Coach drove with no issues. Stopped several times to look for any additional problems. Let the engine run for 30 minutes while we had lunch. No sign of a leak. Crossbar dry. Same with a fuel stop mid-afternoon.

Last night when we stopped in campground, once again no sign of leak. Could be slow enough that the wind driving down the road keeps things dry.

My plan is to check carefully this morning and proceed on to MOT. 160 miles to go.

So questions:

1. Is the electronic lift pump mechanically driven or electrically driven? Just curious how it works.

2. I plan to ask MOT to look at the problem but I'm not sure they are really able to address engine issues. If not, any recommendations on a place in Nac for service? I also plan to spend a day at FOT getting parts and doing some other small repairs (eg. cabinet struts and a new fuel sender). They may be an option if I can get into the service department schedule.

3. Any other considerations or suggestions for me?

Thanks,

Rich

Re: Leaking Lift Pump

Reply #1 – December 05, 2021, 08:23:42 am

Rich,

I don't know which fuel injection system you have, so this may not apply. I recall Don and others have had various problems (including leaks) with the electronic lift pump on the electronic 8.3. The links below may or may not apply to your coach:

99' U270 Fuel Leak

Cummins ISC CAPS intermittent stop engine light (long!)

Re: Leaking Lift Pump

Reply #2 – December 05, 2021, 08:44:31 am

Chuck,

Thanks! It looks like from one of Don's early comments, the lift pump is just used for the first 30-60 seconds on startup to feed the CAPS pump. So if I can get it to start this morning, I should be good to go. That may explain why the leak stopped after I started traveling.

Rich

Re: Leaking Lift Pump

Reply #3 – December 05, 2021, 08:46:27 am

Quote from: Rich Bowman – December 05, 2021, 08:44:31 am

Chuck,

Thanks! It looks like from one of Don's early comments, the lift pump is just used for the first 30-60 seconds on startup to feed the CAPS pump. So if I can get it to start this morning, I should be good to go. That may explain why the leak stopped after I started traveling.
Rich

Not necessarily. The main issue is that it can suck air into the system. That significantly increases likelihood of failure of the CAPS pump.

Re: Leaking Lift Pump

Reply #4 – December 05, 2021, 08:52:26 am

Just in case the problem requires some type of mechanical intervention, here's another recent thread that provides some numbers $$$ on parts and labor to replace both the lift pump and the injection pump.

Injector leak? ISC350 (Read down from Reply #25 on)

Re: Leaking Lift Pump

Reply #5 – December 05, 2021, 08:55:14 am

Brett,

Is it true that the lift pump only runs on startup?

Rich

Re: Leaking Lift Pump

Reply #6 – December 05, 2021, 09:51:52 am

Quote from: Rich Bowman – December 05, 2021, 08:55:14 am

Is it true that the lift pump only runs on startup?

Not Brett, but I believe the video below answers your question. "Lift Pump" starts at 1:30 mark.

https://www.youtube.com/watch?v=xp-YuZ5uQYY

Re: Leaking Lift Pump

Reply #7 – December 05, 2021, 09:54:27 am

Quote from: Rich Bowman – December 05, 2021, 08:55:14 am

Brett,

Is it true that the lift pump only runs on startup?

Rich

Yes. Go stand by the right rear of the coach. Have someone else turn the ignition on (not to start). You will hear the electric lift pump cycle on and then off.

Re: Leaking Lift Pump

Reply #8 – December 05, 2021, 12:49:46 pm

Thanks, that's how I saw it work this morning. The leak stopped as soon as I got the engine started. Made it too MOT.

Any suggestions for service in Nac if they can't address the problem.

Rich

Re: Leaking Lift Pump

Reply #9 – December 05, 2021, 12:53:51 pm

Quote from: Rich Bowman – December 05, 2021, 12:49:46 pm

Any suggestions for service in Nac if they can't address the problem.

https://nacogdochesmotorhomes.com

Re: Leaking Lift Pump

Reply #10 – December 05, 2021, 01:30:41 pm

Rich, leaks there are generally due to low Sulphur fuel as it affects the gasket between parts. I replaced the one on the old coach just to be safe. Yes it only runs for just under 30 secs. Good way around it and a big helper in saving the caps pump is to install a Fass fuel pump to push the fuel to caps so releases a lot of sucking work for that pump, and saves a lot of money by not having to replace caps pump etc.
Johnh

Re: Leaking Lift Pump

Reply #11 – December 05, 2021, 02:07:29 pm

Yes, the leak of diesel OUT will stop.

But, that will still allow AIR to leak in as it is on the suction side of the CAPS pump.

There is an improved Cummins replacement. And, I would stick with Cummins, not any "made to replace" pump, since a failure can cost you a lot of $$ for a CAPS pump.

Re: Leaking Lift Pump

Reply #12 – December 06, 2021, 08:33:25 pm

UPDATE - MOT was able to tighten the mounting bolts and the leak stopped. Now good to go.

Almost the cheapest part of the visit ;-). Only the replacement valve stem extender was cheaper.

Rich

Re: Leaking Lift Pump

Reply #13 – December 07, 2021, 08:32:55 am

Rich,

Keep a close eye on it. That is a very well known failure point and if let go (i.e. air leaking into fuel system with engine running) it can take out the very expensive CAPS pump on your engine.

Were it me, I would replace the pump and gasket at your earliest convenience with the updated/improved Cummins pump (NOT a cheap knockoff).

Re: Leaking Lift Pump

Reply #14 – December 07, 2021, 08:35:39 am

It leaks because the modern diesel, missing certain lubricants, causes the gasket between the drive section and fluid transfer section of the pump, to shrink over time. The pump itself is a centrifugal sliding vane type, very similar to many Hydraulic transfer pumps which are usually very robust pumps. As it only runs 30-40 seconds during a start cycle, to prime the capps pump and void the system of any air, the little electrical drive section should last a life time. The gasket is the weak link. If the gasket fails, its not the Diesel coming out that is the problem, But as Brett states its the air getting sucked in that is what can cause damage to the Capps pump itself. If that happens your looking at $4-9k in repair costs.

Mine started leaking no too long after we acquired the RV. I very lightly snugged the 3 bolts, but also noticed that one really did not want to do so as it felt as if it might be stripped. All the same the light tight I did at that time did stop the leaking.....so I thought.

When I questioned MOT about the system during pre inspection, and the possibility of the lift pump leaking, they declared that they have NEVER ever heard of a capps pump failure and to not worry about it. Like to suggest that the Cummins engines in our FT's were built to some higher standard. They did mention that they had tightened the 3 ,1/4 - 28 (7/16" hex head) bolts on several units over the years and this usually fixed the problem. (these bolts are located on the top of the fluid transfer section, pointing downward into the pump body) All that tightening the bolts on a wore out gasket accomplishes is to buy some time against the inevitable. Not to include that eventually you WILL strip a bolt.

Allthough we own very top quality built RV's, we have the same CUmmins engine that ALL In the years of the Caps systems have. (8.3 L 98-03)

Ive worked on the rig in my off time since acquiring in May mainly to replace any and all things that were 20 years old and could possible fail on the road, hoses,belts, coolant,fluid changes etc... , Short road trips occasionally but nothing more than maybe 30 miles.

A few weeks back we decided we were going to do our maiden shake down cruise, when pre-trip I noticed that our pump was once again leaking. This time I decided to pull it and quickly found that yes indeed one of the bolts was stripped. In the process I also replaced the very firm 20 year old lift pump gasket. I keep all sorts of gasket materials on hand and had a sheet of the proper thickness Buna-n/Nitrile rubber, coated with a very tiny bit of #2 permatex. Of course I had to drill and helicoil the bad thread that possibly MOT had stripped. But at least for now mine has been properly repaired for anotherr 20 years. For those that dont want to make their own gaskets, here is a reliable source for one. But you can buy a sheet of Buna-n/Nitrile rubber to make a few dozen for the same price.

Cummins 4928511 Primer Pump Gasket | eBay

You have to know your engine VIN as it appears Cummins had 2 differenet gaskets for that lift pump. This link would have worked for my VIN. The sellers page explains this.

I myself, due to the issues with many of these system out there, have opted to upgrade my system to a constant flow FASS Titanium series fuel system. This system removes ALL air pre-caps and feeds the caps constant instead of the Caps having to constantly long distance suck. But at the same time leave the OE lift pump in place as an emergency backup. I just need to get my tank empty as I also want to do my fuel lines at the same time. We plan to use our RV in the coming years to travel the entire 49 landlocked as well as parts of canada. I would prefer to have a more robust system than the OE design. But that is just me. Your unit is near the same vintage as ours, I would strongly consider a gasket replacement at a minimum if your able to do so. If not, maybe a New CUMMINS (not aftermarket pump) A damaged Caps pump is not a breakdown that the DIY can easily handle on a roadside without lots of time and of course a compatible pump that most would never carry due to the cost.

Re: Leaking Lift Pump

Reply #15 – December 07, 2021, 09:14:26 am

Better check the bolt thread size again. I never heard of 1/4-24 thread size. Only 1/4-20 UNRC (coarse thread) and 1/4-28 UNRF (fine thread).
Maybe 5/16-24 UNRF ? (fine thread)?? Federal Specification FF-S-86d
A quick way to tell if 1/4 or 5/16 thread is to measure the hex head bolt size. 1/4 thread will have a 3/8" hex while a 5/16 thread will have a 1/2" hex.
(nominal thread size x 3/2. In other words 1(numerator) x 3=3 while 4(denominator) x2=8. Thus 1/4 x 3/2 =3/8 hex.)

Re: Leaking Lift Pump

Reply #16 – December 07, 2021, 09:17:25 am

My bad a typo, 1/4-28 is correct.....1/4" fine

Re: Leaking Lift Pump

Reply #17 – December 07, 2021, 09:26:59 am

Not bad. Been there--Rocket (our 19-1/2 year old cat) thinks he can type so I get blamed for mistakes. (and I am sticking to that for the reason for my mistakes)
You would think he would have learned to type and spell by now!

Re: Leaking Lift Pump

Reply #18 – December 07, 2021, 09:33:00 am

1/4 inch has 7/16 head if not a specialty bolt.

Re: Leaking Lift Pump

Reply #19 – December 07, 2021, 09:37:14 am

Oops!! See? I told you Rocket can't spell or type!

Re: Leaking Lift Pump

Reply #20 – December 07, 2021, 12:45:48 pm

Baaad kitty....

Re: Leaking Lift Pump

Reply #21 – December 07, 2021, 06:33:19 pm

Mike,

Thanks for the great writeup. I'll plan to pull and check the pump when I get home and then install with a new gasket.

Rich

Re: Leaking Lift Pump

Reply #22 – December 08, 2021, 08:17:44 am

Rich,
You are more than welcome,I also did not know about this design when I was searching for an early 2000 vintage RV, but quickly found out about it. As I diy all of my own equipment, I learned as much as I could about the design, its weaknesses as well as ways to improve if possible.I even spoke to a few old Cummins guys I knew, whom all talked about the system in the same respect. CAPS fuel injection was not exactly a very proud moment for Cummings back in that day, evident by the fact they did not stay with it very long. But at the same time, not a reason I would walk away or avoid an 8.3 of that vintage. The 8.3, not fully electronic controlled engine has a strong reputation for being a long haul bullet proof engine and still somewhat easy for the DIY to work on. Every piece of equipment in this world designed by man has a weak link somewhere. For these its this goofy lift pump gasket.

What fascinates me is how MOT, whom really seems to care for its customers and the overall condition of our coaches, seems to be very non informed on the subject. When I asked about it, they replied I must have gotten 3rd world misinformation they know nothing about such an issue. These engines were used in countless vehicles around the world, not just RV's. And there have been countless incidents of failures, and well documented cases and write ups on the subject. Even Cummins TSB's published so I was told. (Limited write ups/info in the RV forums world). To state that they knew to tighten the bolts as a temporary fix, clearly shows they know about it. To me, if they know to tighten the bolts, they should also inform the customers of the History of the issue as well as a suggested fix (replace gasket or pump or upgrade) Not just slap a band aid on it and let the customer head on down the road to a possible very bad situation.

FYI.....it not a terrible hard Job, lift your bed and look for the top of the lift pump, located near the front end of the engine passenger side.
Obtain your Gasket or Gasket material before you start.

Disconnect the electrical connector from the pump, thats usually quite fun as it probably never been removed and full of gunk on the locking slide.
The bolts are probably hid under a bunch of wire tied cables/hoses etc. I found it easier to deal with after I cut a bunch of wire tires. Get you a large tote that will also fit under your engine as while you work on this thing you are going to lose about 1-3 gallons of diesel fuel. Raise the coach on safety stands will give you more room for the tote. The 3, 1/4 bolts are in a triangular pattern probably crusted up black in crud. Loosen but not remove them so that the fuel within will start to come out into your tote below.

You will need two large box end wrenches seems I recall a 1" and a 7/8" was what I used, but now that I think more about what I did, you will probably only need to remove the Supply fuel line which is the larger of the two. The closer to the block is the return line and is not in the same liquid path as what you will be working on. You might could just drain the fuel bowl on the filter by the batteries that feeds the pump. However you do so, you need to make sure no fuel is going into the pump body and that you catch it.

Once fuel quits dropping from the pump remove 2 of the bolts, with your other hand and a large rag wrapped around the pump and still holding onto it, or use a box or something to catch it, remove the last bolt and lower the pump body straight down out and up. I state this particular way as it may come down with the body and gasket stuck to one another or it may come down with the gasket stuck to the fluid path manifold. If it does the latter, small parts could hit the floor. (another reason for a large tote) The fuel impeller with its movable vanes can easily drop a few parts and pieces if you tilt it. If it does, dont worry the Vanes are rounded on both sides and it really doesn't matter which way they go back. Get it all on the bench, While out clean the pump body in a parts washer making sure not to get much if anything inside of the pump cavity. I used a can of carb cleaner and gently blew out the pump cavity and the impeller vanes before reassembly. The impeller goes in if I recall on a shaft, the veins slide into ports on the impeller. I tiny dob of grease on the back side of each vane where it goes into the impeller would help hold them in place and not hurt the situation as it will dissolve in diesel. Put the top impeller plate back on, it will have a circular worn pattern on it, the worn side mates to the impeller, topped by the NEW gasket. Now me personally, I never install a solid rubber, paper or cork gasket without a tiny bit of adhesive on both sides wherever they mate with metal bodies. Permatex #2 is prefect for this application.

Using acetone or similar, clean the Fluid path manifold where the new gasket will mate.....this ain't easy as you have to do it by feel and a mirror. Or maybe lay under the rv and reach up IF all diesel has quit dripping.
If you have a helper, have them on top to do the screws while you perfectly vertical lift the pump body into place. (this is where those vanes might jump out of the impeller if your not careful.) Once in place and screw started tighten until you feel a good snug fit, if I had to give a torque spec I would guess 89-98 in/lbs. Me personally I put a small amount of the blue locktite on the screws for added back out security.

Reconnect the electrical connector to the lift pump.
reconnect the fuel line, or filter bowl.
Using the ignition key, but not cranking. Run the pump through 3-5 pre start cycles, where it will run 30-45 seconds . This will get all the air out of the system and put fluid path back into its proper operating state. As your cycling this little pump quite a bit ( more than its used to), Maybe wait a minute or two between each cycle so as not to overheat or stress it. **Note** the very first cycle will sound a bit noisy from the pump as all of its internal pieces realign and the diesel start to lubricate the parts.
On the last one go ahead and let the engine crank. Check for any obvious leaks. Clean up the mess all the dripping diesel created.
I road tested and checked several times over a few days.

I am glad my shared information helped you. I surely appreciate it when others do the same for me.

Re: Leaking Lift Pump

Reply #23 – December 09, 2021, 08:52:05 am

Mike,

Sorry for the late reply. As you probably noticed, I got distracted yesterday with another problem.

Thanks for the great writeup. I'm sure it will help others besides me.

Rich

Re: Leaking Lift Pump

Reply #24 – December 09, 2021, 09:27:04 am

For what it is worth, after spending most of my working career as a machine designer and assembler, if you don't have any blue Loctite handy, silicone sealer makes a good insurance adhesive against bolts coming loose on their own from vibration.
We used it a lot because of the limited shelf life of most Loctite products at the time.

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