Fuel leak on 2000 Diplomat ISC engine

[pulsarjab]

Need a little help. Pulled into Florida and noticed fuel leaking, when engine running, from I think the lift pump. I have contacted local Cummins shop and took pictures, they need a part number. Does anyone have this information? I see many have changed out to a FASS system but I am needing a quick fix and will address that latter.

[cbr046]

There's 3 bolts on the top of the lift pump that you can try to tighten.  They're accessed from the bedroom / closet hatch from the top, and one is challenging to get to.  This sometimes fixes the leak, but it's temporary at best.  It worked on mine . . . . once. 

The real issue isn't the fuel leaking out but, as the lift pump only operates for the first 30 sec, you'll have air being sucked into the main fuel pump. 

You can buy a new lift pump at whatever cost ($$$) and it will probably last as long as you keep the coach.  Or you can bite the bullet, install a FASS system and bypass the lift pump FOREVER, plus it gives your CAPS or HPCR fuel pump a break by not pulling all the way from the main fuel tank.  And if you ever have to replace one of those . . . . . well, it's a LOT of dollar signs!

- bob

[Jim Pratten]

Ditto what Bob said.

Search this forum for “lift pump bolts” and you find several thorough discussions with pics.

Lift pump part number should be accessible on Cummins Quickserve system.  You need to register which takes just a few minutes. You’ll need your engine serial number. 

[Robert U]

I had the same problem on my 2000 Dip. I tightened the 3 bolts and it took care of the problem. A few years later the leak returned. I had the lift pump replaced. It cost me about &1000. Did not fix. I had a leaking return line. They repaired it as a final fix. 
Bob U. 2000 Dip

[Ivan K]

Cummins should absolutely know the part number from your engine's ESN if you buy it from them or have them to do the replacement, just like you can find it yourself as mentioned above. Surprised they did not tell you that.

[Ivylog]

Doubt your leak is the lift pump since it’s leaking when the engine running… should be suction on it, not pressure.

[jacwjames]

Where exactly did you see fuel leaking???

With the engine running the CAPS pump pulls fuel all the way from the fuel tank, the fuel line has (-) negative pressure.  There can be a slight seep from the lift pump but it wouldn't leak much fuel.  

But there is a fuel return line that goes through the lift pump housing and sends unused fuel all the way back to tank.

There are high pressure lines from the CAPS pump to the injectors, I guess it is plausible that one of these could be leaking. 

So you might take the time to investigate where the leak is. 

Edited January 30 by jacwjames

[bobdinsmore]

I have a 2000 Diplomat ISC 315HP. I have had two fuel leaks in the Lift Pump area and neither was the problem the pump. The first time was the three bolts holding down  the pump top cover. Tightening the bolts fixed the problem; that was about five years ago. The second case was a corroded steel fuel line leaking through the side wall. I was on the Interstate so could not wait for over-night parts delivery unless necessary. The mobile diesel mechanic was able to weld the line; that has been OK for the past year.

I have two mobile diesel mechanics I have used in Florida very successfully. I found both competent, reasonable and came right away when they said they would:

              Tampa:               https://www.nextleveltruckandjeep.com/

              Fort Myers:        https://www.alignable.com/fort-myers-fl/big-rig-mobile-truck-services        

I highly recommend Big Rig in Fort Myers, the best I ever have worked with.

Bob Dinsmore

                  

 

[pulsarjab]

UPDATE.............First, I want to thank all of you for the support. We have enjoyed our Diplomat for 15 years and this is the first major issue we have had and we have 128,000 miles on it. Things do wear out, ask my doctor. Anyway, first issue, Cummins needs to know the engine serial number in order to identify the part, I spent 45 minutes on the phone with support but was not able to read number. They suggested I get a shop to identify the serial number by reading the onboard computer. I also contacted www.monacocoach.com and gave then the Vin number, They were able to provide the engine serial number. I contacted a local shop Cummins recommended, just a mile from my location, and they were able to verify serial number, checked the leak, and ordered the parts, The parts arrive latter this week and will be installed by them. As everyone knows, inflation is affecting everything and diesel parts and good mechanics are no exception. Five hours of labor and $500 in parts is not cheap, but considering the service, I am dancing. Thanks again for all the help. I was not able to locate the three bolts on the top of the pump but after all these years of good service, replacement was a logical step and a big relief.

[jacwjames]

Can you tell us what part had to be replaced, I keep a data base of parts that "might" go bad on my engine. 

[pulsarjab]

It has been called the lift pump. It comes on briefly each time you turn the key on, to build fuel pressure.

[MyronTruex]

Remind him to take some pictures for posting when he is under there repairing his battery box.

 

[jacwjames]

Odd that it was leaking while the engine is running but good that they found it.  It is a common problem.

The original lift pump was problematic at best.  Originally Cummins had a TSB on it and the shops were initially advised to change it but my guess is that it was costing them $$$$ so they changed it to replace the small gasket and then eventually just left it up to owners to deal with it. 

I was aware of the problem and kept an eye on it.  In 2021 I took it for a drive and when brought it back I crawled underneath to clean my jack stems and heard the his of liquid hitting the exhaust.  Sure enough fuel leak but it wasn't hitting the ground.  I tightened the 3 bolts on top and that stopped the leak but I thought about long term fix which for me was to install a FASS transfer pump an bypass the lift pump.  Cost for me to do it was ~$1000 but long term is it a good upgrade not only for positive ~15psi to the CAPS pump all the time but also the additional filtering. 

But at least you found the problem but keep an eye on it.  I believe the new version of lift pump is not serviceable but can still potentially leak.

[VinceB]

On 1/31/2024 at 5:39 AM, pulsarjab said:

UPDATE.............First, I want to thank all of you for the support. We have enjoyed our Diplomat for 15 years and this is the first major issue we have had and we have 128,000 miles on it. Things do wear out, ask my doctor. Anyway, first issue, Cummins needs to know the engine serial number in order to identify the part, I spent 45 minutes on the phone with support but was not able to read number. They suggested I get a shop to identify the serial number by reading the onboard computer. I also contacted www.monacocoach.com and gave then the Vin number, They were able to provide the engine serial number. I contacted a local shop Cummins recommended, just a mile from my location, and they were able to verify serial number, checked the leak, and ordered the parts, The parts arrive latter this week and will be installed by them. As everyone knows, inflation is affecting everything and diesel parts and good mechanics are no exception. Five hours of labor and $500 in parts is not cheap, but considering the service, I am dancing. Thanks again for all the help. I was not able to locate the three bolts on the top of the pump but after all these years of good service, replacement was a logical step and a big relief.

 

Just went through this with my '01 Dip that has the 330 ISC.

Yep - 5 hours labor and about $500 for the pump.  Plus about $20 for a new harness to fit the new pump.  So make sure you have them find out if you need the the harness and order the harness at the same time as the pump.