Replaced leaking lift pump

Topic: Replaced leaking lift pump - dying engine (Read 1717 times) previous topic - next topic

Replaced leaking lift pump - dying engine

April 15, 2019, 03:36:27 am

Thanks in advance for any assistance. With the great advice of all of you on this forum I replaced my leaking mechanical fuel pump on the 8.3. I am now experiencing issues with keeping the engine prime and the engine running at idle. In order to start the engine yesterday & today I had to manually pump the primer until the overflow squeaked. The engine started immediately and drove around for 30 minutes with no issues. When i was putting it back on the driveway and leveling it wants to die off after a couple of minutes of idling with no restart until I prime the fuel pump. It takes about 15-20 pumps before I hear it squeak.

Am I right to possibly assume I received a bad lift pump? It seems to work ok while driving and priming? I am thinking about just replacing it again due to the fact I had no other issues before I replaced it. For a little more info I did replace the banjo bolt washers to ensure no leaks.

If anybody has any additional ideas I should be looking at I am all ears.

Thanks,

David

Re: Replaced leaking lift pump - dying engine

Reply #1 – April 15, 2019, 06:34:02 am

Since you are having to prime to start repeatedly, sounds like to me, you have air entering the supply line, causing fuel to run back into the tank. Did you open anything else in the fuel line that could maybe be leaking air, injector, hose, etc?

If not, then I would expect your removing the pump may have opened a crack on the hose supplying fuel to the pump. That happened to me. After replacing fuel pump like yours, you can see, my Reply 15, middle picture when you expand, the slight crack going over the wavy barb in the hardened hose connector. (Expand the picture to see). If you see a similar crack you might get away with splicing in a new piece to pump as a temporary fix, soon you will need to replace the entire line.

Do you know if your fuel lines have ever been replaced?

There are many posts, including mine, on replacing lines.
Fuel Line replacement

Re: Replaced leaking lift pump - dying engine

Reply #2 – April 15, 2019, 08:00:23 am

Jack,

I will inspect the connections and lines when I get home off of night shift. They looked good to me and did not see anything obvious while working on them. I keep reading reference to air getting in the lines? I would have assumed if I had a leak it would be spraying or leaking diesel off of the hose or connections. Everything is dry when checking which may be the case with a leaking line?

Thanks,

David

Re: Replaced leaking lift pump - dying engine

Reply #3 – April 15, 2019, 08:27:00 am

David,

A leak on the SUCTION SIDE will rarely show a fuel leak, as it is under zero pressure when at rest and negative pressure when the engine is running. Yes, if level of fuel in tank is above the level when the leak is occurring, there will be some very minimal pressure.

Re: Replaced leaking lift pump - dying engine

Reply #4 – April 15, 2019, 09:01:35 am

Quote from: Jack Lewis – April 15, 2019, 06:34:02 am

If you see a similar crack you might get away with splicing in a new piece to pump as a temporary fix, soon you will need to replace the entire line.

It's possible that reinserting the barb further up the old line could cause any cracks to open up and leak.

Re: Replaced leaking lift pump - dying engine

Reply #5 – April 15, 2019, 09:33:12 am

The link in Jack's post (above) is not working for me, so I can't see where he found the cracked fuel line. ?

If David's hand prime pump works, and builds pressure so the overflow valve "squeaks", then they both appear to be functioning properly.

The "barbed fitting" and "push-on hose" are not used on my C8.3 mechanical lift pump. The OEM braided line from the frame mounted fuel filter to the lift pump has steel JIC swivel fittings on both ends. Not much possibility of leak at that point, as long as the fitting is firmly snugged up.

From the frame mounted filter back to the fuel tank is another matter. I have not messed with that line. I think it unlikely that replacing the lift pump would suddenly cause a leak to appear in that line. I suspect David's problem is "something else" but I'm really scratching my head trying to imagine where the air is getting into the line.

Photo below of the new lift pump on my coach, with braided inlet fuel line visible:

Re: Replaced leaking lift pump - dying engine

Reply #6 – April 15, 2019, 09:54:05 am

OK, I found the fuel line replacement thread with excellent instructions by Chris and Jack. A very good primer on doing a difficult job!

Fuel Line replacement

More to the point of this thread, photo below shows the old hose connected to Jack's lift pump, with cracks showing. His hose was a different construction than what I have on my coach. So if David has the same type hose as Jack, then this is a place to check for possible air leaks.

Re: Replaced leaking lift pump - dying engine

Reply #7 – April 15, 2019, 10:05:06 am

If you fill the tank and then park the coach where the tank is uphill and the engine restarts perfectly the fuel lines are suspect

Re: Replaced leaking lift pump - dying engine

Reply #8 – April 15, 2019, 10:26:11 am

A good way to test for a suspect fuel line is to replace the suction side with a fuel container just outside the engine compartment. Run a new, short fuel line to the primary filter. Once it runs and then you shut it off, you can check to see if it starts and idles normally later in the day.

This is the test I have always used with great success. I found that the supply line for the 10K generator was leaking with a million tiny cracks and once I replace it, it ran fine.

Cummins lift pumps are always suspects so a good possibility the pump is the problem. I installed a pressure gauge on the output of the secondary pump and at the pressure side of the hand primer pump so easy to check for incoming leaks as well as pressure to the unit injectors.

Another way is to pinch off the engine supply line at the tank and use a Mitty-Vac on it back at the engine. Might be hard to reach the fittings on some models.

Pierce

Re: Replaced leaking lift pump - dying engine

Reply #9 – April 15, 2019, 10:51:21 am

Chuck,A plus for cleanliness.

Re: Replaced leaking lift pump - dying engine

Reply #10 – April 15, 2019, 10:54:28 am

Quote from: wolfe10 – April 15, 2019, 08:27:00 am

David,

A leak on the SUCTION SIDE will rarely show a fuel leak, as it is under zero pressure when at rest and negative pressure when the engine is running. Yes, if level of fuel in tank is above the level when the leak is occurring, there will be some very minimal pressure.

So true, as these pictures show, I had very hard, brittle hose, with many cracks, however with little leakage of fuel.

In the picture of all the removed lines, you can see some of the generator fuel line (blue in color) had been spliced by unknown repair shop of previous owner.

Shared album - John Lewis - Google Photos

Re: Replaced leaking lift pump - dying engine

Reply #11 – April 15, 2019, 11:10:53 am

Suction lines with cracks will often be damp, especially the generator's as it has a slight constant pressure on it. Engine supply lines may not as they are a little higher than the fuel tank.

Nothing wrong with a splice as the heat and or abrasion may degrade the hose in the vicinity of the engine while the rest is OK.

If running new hoses, use expandable braided conduit cable weave hose cover to slide over the new hose. Makes it 10X easier to install. Use the same size as the hose as it will expand to fit and when snug, it makes it super easy to slide.
5/8" 100 ft. XSCORPION Expandable Braided conduit Cable Weave hose cover...

Our Detroit's hoses and wiring use it OEM in the engine area. Also keeps diesel spray to a minimum in case of a high pressure crack/failure.

Pierce

Re: Replaced leaking lift pump - dying engine

Reply #12 – April 15, 2019, 12:32:28 pm

Talked to another mechanic,some of the lift pumps have a built in check valve some don't,try putting the old one back on if the
leak is not that bad,if the problem stops it's the pump.You can still find then few and far between made in USA,I got a Carter a
couple of years ago made here.

Re: Replaced leaking lift pump - dying engine

Reply #13 – April 15, 2019, 01:43:58 pm

I suppose the OP's problem here could be the new replacement lift pump. Don't know where David bought the pump.

When I went shopping 5 years ago to replace my OEM pump, I took the recommendation of one of the online diesel "experts" who told me that all the replacement mechanical lift pumps for Cummins engines are made in China. Said it doesn't really matter what brand name is on the box. The "expert" I talked to recommended the Alliant pump in the link below, so that's what I bought. It has performed admirably for 5 years. I have a fuel pressure gauge installed between my lift pump and injection pump, so I know what pressure my lift pump is producing at the injection pump inlet. I agree with Pierce - I think this should be a mandatory mod for every diesel coach owner. A fuel pressure gauge is a invaluable aid in diagnosing and trouble shooting fuel delivery problems. It is quite simple to install a gauge on the Cummins engine - other brand engines might be slightly more complicated. See link below for my gauge installation:

Fuel System Science Project

So, are all "made-In-China" lift pumps the same quality? I don't know. Is a pricey "Made-In-China" pump better than a cheap "Made-In-China" pump? I don't know. Is a GENUINE CUMMINS "Made-In-China" lift pump superior to other "No Name" Chinese pumps? I don't know.

You pays yer money and takes yer chances.

Pump I used (works great): Alliant Power | AP4988747 | Fuel Components | Thoroughbred Diesel

More money: Amazon.com: Genuine Cummins 4988747 stock fuel lift/transfer pump for 94-98...

Carter (made where?) pump: Amazon.com: Carter M73104 Mechanical Fuel Pump: Automotive

Really Cheap (junk?): Amazon.com: AUTOKAY Diesel Fuel Lift Pump 3936316 P7100 for 94-98 Dodge Ram...

Re: Replaced leaking lift pump - dying engine

Reply #14 – April 15, 2019, 03:31:55 pm

Quote from: Chuck & Jeannie – April 15, 2019, 09:33:12 am

There is no "barbed fitting" and no "rubber hose" used on the C8.3 mechanical lift pump. The OEM braided line from the frame mounted fuel filter to the lift pump has crimped JIC swivel fittings on both ends. Not much possibility of leak at that point, as long as the fitting is firmly snugged up.

Sorry, mine has the Push Lok fittings with the barbs same as Jack's in the picture.

Re: Replaced leaking lift pump - dying engine

Reply #15 – April 15, 2019, 04:03:30 pm

Quote from: Travelin' Man – April 15, 2019, 03:31:55 pm

Sorry, mine has the Push Lok fittings with the barbs same as Jack's in the picture.

Yes, after seeing Jack's photo (which I posted in the next reply #6) I realized there must have been a change in the fuel supply hose design after my coach was built. My '93 has a braided line with steel fittings, and Jack's '97 and your '03 have the rubber hose with Push Lok brass fittings. I'm not sure which type hose David has on his '94 model. That is why I said (in Post #6):

"So if David has the same type hose as Jack, then this is a place to check for possible air leaks."

Re: Replaced leaking lift pump - dying engine

Reply #16 – April 15, 2019, 04:16:23 pm

Have the JIC fittings on mine,some of the hoses are blue.

Re: Replaced leaking lift pump - dying engine

Reply #17 – April 15, 2019, 08:24:58 pm

Quote from: Chuck & Jeannie – April 15, 2019, 01:43:58 pm

So, are all "made-In-China" lift pumps the same quality? I don't know. Is a pricey "Made-In-China" pump better than a cheap "Made-In-China" pump? I don't know. Is a GENUINE CUMMINS "Made-In-China" lift pump superior to other "No Name" Chinese pumps? I don't know.

You pays yer money and takes yer chances.

The last 9 years we worked, Lynn and I were employed by a Tier II automotive manufacturer. After your contract is over and if you don't care to do more work for the same company you still own everything to make the product. The question now is, will you maintain the same standards demanded by the automaker?
FWIW if you're making auto parts and you have a problem that gets by the manufacturer and it causes a recall, the cost is on you.

So yes, the Cummins pump is probably better and you have some recourse if there is a problem.

Re: Replaced leaking lift pump - dying engine

Reply #18 – April 15, 2019, 11:22:21 pm

Thank you for all that have replied and appreciate the input. I was called back in for a double shift at work today..... will take a look at it tomorrow and report back with my findings.

Chuck, I did purchase the pump you linked previously from Alliant. The pump seems good. Even hand priming slowly produces diesel to the overflow. I am hoping it is not the fuel line but at a loss also...

David

Re: Replaced leaking lift pump - dying engine

Reply #19 – April 15, 2019, 11:52:03 pm

When you say "hand priming slowly produces diesel fuel to the overflow", where is your overflow, are you loosening one of the injector lines and then re tightening?

Re: Replaced leaking lift pump - dying engine

Reply #20 – April 15, 2019, 11:55:45 pm

Unless he means going back to the fuel tank.

Re: Replaced leaking lift pump - dying engine

Reply #21 – April 16, 2019, 01:37:42 am

Quote from: Jack Lewis – April 15, 2019, 11:52:03 pm

When you say "hand priming slowly produces diesel fuel to the overflow", where is your overflow, are you loosening one of the injector lines and then re tightening?

Most all diesels except some CATs, return the majority of fuel to the fuel tank. There is a spring loaded valve, either located at the injection pump or in our case after the last unit injector to keep pressure and not allow fuel to run to the tank after the engine is shut off making it much harder to start the next time. It's a must to keep the fuel system full without letting air into the system.

A good hand pump will generate more pressure than the relief valve allows so will send the excess fuel back to the tank.

This return/relief valve can wear, get deposits on it, etc. This is a reason to occasional check to see if it's leaking and not allowing specified pressure to be in the injection pump. Low pressure will cause a loss of power and hard starting plus may cause increased wear due to insufficient lubrication.

This is one of the reasons that I installed a pressure gauge on the output side of the secondary filter. Other reasons include filter conditions as well as lift pump operation.

This is what a Bosch overflow valve looks like on a Bosch "P" pump: Amazon.com: 1417413047 Disel Pump Overflow Valve for Dodge Cummins 5.9L...

Most all diesels need them from simple mechanical diesels to cutting edge high pressure common rail engines. A video to explain them here:
https://www.youtube.com/watch?v=Hxpq1LfG584

Pierce

Re: Replaced leaking lift pump - dying engine

Reply #22 – April 16, 2019, 08:06:59 am

Quote from: Pierce & Gaylie Stewart – April 16, 2019, 01:37:42 am

This is what a Bosch overflow valve looks like on a Bosch "P" pump: Amazon.com: 1417413047 Disel Pump Overflow Valve for Dodge Cummins 5.9L...

Thanks, Pierce, for the excellent video link! They do make it sound like the valve they are discussing only comes into play when occasional high fuel pressure conditions exist. On the Cummins engine (with mechanical lift pump and P7100 injection pump) the overflow valve is always actively working to keep fuel pressure constant anytime the engine is running. It is just a ball & spring valve. The spring can weaken over time, allowing the fuel pressure to decline to less than optimum levels. Trash can block the ball from seating. Either condition will adversely affect fuel pressure.

If anyone is going to all the trouble (yes, it's a tough place to get at) of checking/cleaning/replacing the overflow valve on a Cummins with P7100 injection pump, then double down yer bet and install the ADJUSTABLE valve from Tork Tek. Well worth the extra cost.

Cummins Adjustable Overflow Valve by Tork Tek - OFV010

See my shiny OFV010 valve in the photo below (add some BLING to your drab old engine):

Re: Replaced leaking lift pump - dying engine

Reply #23 – April 16, 2019, 08:29:18 am

While your at it get the gauge adaptor they have,easy to check fuel pressure.

Re: Replaced leaking lift pump - dying engine

Reply #24 – June 26, 2019, 04:30:19 pm

Familyrig, did you ever find the air leak that was causing your diesel to loose prime?

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