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Topic: Leaking Lift Pump (Read 1023 times) previous topic - next topic

Leaking Lift Pump

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 #2 –
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 –
Quote from: Rich Bowman –
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 –
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 –
Brett,

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

Rich

Re: Leaking Lift Pump

Reply #7 –
Quote from: Rich Bowman –
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 –
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 #10 –
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 –
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 –
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 –
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 –
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 –
 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 –
My bad a typo, 1/4-28 is correct.....1/4" fine

Re: Leaking Lift Pump

Reply #17 –
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 –
1/4 inch has 7/16 head if not a specialty bolt.

Re: Leaking Lift Pump

Reply #19 –
Oops!! See? I told you Rocket can't spell or type! :))