new lift pump made a BIG difference

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new lift pump made a BIG difference

December 12, 2014, 11:57:21 pm

Our coach runs fine, but a few months ago there was discussions about changing lift/transfer pumps, so we decided to replace our original pump. The pump is located on the side of the engine and its job is to pull diesel from fuel tank through primary fuel filter and then push the fuel through the secondary fuel filter and up to the injector pump. The pump output is around 12 psi.

We installed the pump ourselves about a month ago and this week we drove through Texas heading west and reaped the benefit of the new pump.

We originally considered changing to an electric pump, but decided for the first step to change the mechanical pump. With our good results, we will probably not use an electric pump.

We are very surprised how much BETTER our coach is driving and handling the hills of west Texas. We had no idea that our original pump was not doing the job. Back during the original discussions, some posted that they recommended if it is not broken, don't touch it. We are thrilled we changed out our transfer pump. We did not change fuel filters when we changed the pump, so the improvement was not from new filters.

We have more power on hills, with engine holding speeds better and less and softer downshifts, maybe running cooler. Installing the Aero muffler and a new Cummins-brand transfer pump has made a BIG difference for us.

Re: new lift pump made a BIG difference

Reply #1 – December 13, 2014, 12:45:53 am

Barry & Cindy, is your trans pump on the left middle side of engine as you look down at engine standing at foot of bed as mine is? I have looked into changing it too but it seems such a tight spot with cables etc etc running past it. Was it an awkward change?
JohnH

Re: new lift pump made a BIG difference

Reply #2 – December 13, 2014, 09:17:53 am

Another thing that must be checked on mechanical cummins is that the King Controls weakens over time. Long duration of cruise control on mine and the stepper motor "slips" and won't be able to pull the linkage to full throttle. I verified this with tech at King Controls.

Turning off cruise control and releasing pedal usually resets it. But, the first time this happened it seemed like a loss of power.

Re: new lift pump made a BIG difference

Reply #3 – December 13, 2014, 10:12:41 am

Quote

the King Controls weakens over time

Krush,

Did not know about the King Slip, thanks.

We did find that at the end our King throttle cable the slot that pulls the injector pump lever had way too much slack so the first few moments of movement, there was no acceleration. The throttle pedal had a short hesitation when first being pushed. We found this last year, and correcting it made the throttle more responsive.

Re: new lift pump made a BIG difference

Reply #4 – December 13, 2014, 10:12:41 am

Quote

Was it an awkward change?

John, we will soon write-up our fuel transfer pump replacement with photos.

Yes the pump is in on the curb side and yes the install was awkward because hanging over the side of the bed and Cindy getting down on the tranny to help with wrenching. But it is two brass hose fittings and two bolts to remove. If the cam in the engine is full out, the mounting may have some challenges, but maybe not.

Finding the best pump was a challenge as the Cummins 5.9 uses the same style and is a popular truck engine with many pump sellers. Also there are several after-market pump brands, and maybe some pumps that are designed for Bio-diesel mixtures.

Re: new lift pump made a BIG difference

Reply #5 – December 13, 2014, 03:04:11 pm

I took great pains to buy a genuine Cummins pump, it was proudly stamped China. Noted the original pump was mfg in England. I think you made a wise choice in foregoing the electric pump. I do find the new pump will purge air from filter change using manual prime knob in short order. Be sure key is on for purge.

Re: new lift pump made a BIG difference

Reply #6 – December 13, 2014, 06:30:11 pm

Changing lift pump will save you from being stranded along the road. Ours went out just outside of Jacksonville. Illinois and it was just like one turned the key off,

Re: new lift pump made a BIG difference

Reply #7 – December 13, 2014, 08:31:38 pm

Quote from: Chuck Pearson – December 13, 2014, 03:04:11 pm

I took great pains to buy a genuine Cummins pump, it was proudly stamped China.

All the new mechanical lift pumps are made in China - doesn't matter where you buy it or who's name is on the box. I strongly recommend the use of studs rather than bolts...makes it into a "one-handed installation", regardless of cam lobe position. New and old pumps shown below for comparison:

Larryb - LarryB's EASY Stud Mounting Kit for Lift Transfer pump, 12 valve
Fuel Transfer Pump Alliant Power Stock Replacement Dodge Cummins 1994-1998 5.9L

Re: new lift pump made a BIG difference

Reply #8 – December 13, 2014, 09:14:23 pm

John, the fuel transfer pump on my ISC is in the curb side of the engine, and all electric. Not a technical job just hard to get to took me about 2 hours. If you have the new one in your hand it helps you finding the bolts on the old one

Re: new lift pump made a BIG difference

Reply #9 – December 13, 2014, 09:47:02 pm

@Chuck Thanks for the photos! And the studs are a great idea.

see ya
ken

Re: new lift pump made a BIG difference

Reply #10 – December 14, 2014, 08:42:08 am

Bernd replace the lift pump on our C8.3-325 a couple of months ago. Starting was sluggish at low fuel levels, so I asked him to check it for pressure and function. He reported that the old pump was not working as it should. He put on a Cummins pump and reported that the new pump would pick up fuel from a bucket on the floor.

I haven't noticed a difference in general performance, but am confident that the new pump will provide benefits over the old unit.

I expect the new pump may be more compatible than the old pump for use with biofuels.

Re: new lift pump made a BIG difference

Reply #11 – December 14, 2014, 12:34:10 pm

Bruce yeah, I figured ours was electric and looking at Chucks pictures ours is NOT as easy to get off etc. Way more crap in the way and me with my back etc problems. I did look at it from below in the pit a while back and it did not look any easier from below. I will have to look up the part # and get one just in case I need it soon. What Pt # and supplier did you come up with as searching web has not found it. Have the # from Cummins quick search on my eng#. Am thinking that maybe only replace the actual lower electric pump and body and leave rest in place??
JohnH

Re: new lift pump made a BIG difference

Reply #12 – December 15, 2014, 10:06:24 am

Good Morning - When the mechanical lift pump on a c8.3 is changed, do the injectors lose prime? Do they have to be bled, to allow air out of the fuel line to the injectors? If so, is it a difficult process to bleed the injector fuel lines? I currently carry a spare alternator, water pump, fuel solenoid, belts, hoses, etc, yet I am now thinking I should purchase and carry a spare lift pump along with a set of those Easy Stud mounting kit bolts.

Barry - did you change to the resonator at the same time as you changed the lift pump? I changed to straight pipe exhaust on my c8.3 several months ago and it was one of THE BEST mechanical benefits to my coach performance.

Thank you, Jeff

Re: new lift pump made a BIG difference

Reply #13 – December 15, 2014, 11:11:05 am

Quote from: JeffOnLakeConroe – December 15, 2014, 10:06:24 am

When the mechanical lift pump on a c8.3 is changed, do the injectors lose prime?

No, the injectors do not lose prime. Between the lift pump and the injectors, you have the engine-mounted fuel filter (water separator) and the injection pump. You lose very little fuel when you remove the old pump - only what is in the first couple feet of the inlet hose and what is in the short outlet pipe (which goes up to the engine-mounted fuel filter).

Before I changed my mechanical lift pump, I did some online research on the subject. The recommended procedure was to install the pump, then pump the "hand prime pump" (which is part of the lift pump) until you hear the overflow valve "squeaking". This "noise" indicates the lines between the lift pump and the injection pump are filled with fuel. Then start the engine. I followed this procedure, and had no problem getting the engine started after swapping pumps.

Re: new lift pump made a BIG difference

Reply #14 – December 15, 2014, 03:29:48 pm

Quote from: cajk – December 15, 2014, 11:11:05 am

The recommended procedure was to install the pump, then pump the "hand prime pump" (which is part of the lift pump) until you hear the overflow valve "squeaking". This "noise" indicates the lines between the lift pump and the injection pump are filled with fuel. Then start the engine. I followed this procedure, and had no problem getting the engine started after swapping pumps.

Right on, and the new fuel pump primer will work very well and quickly compared to the old, worn out one. I found it helpful to have the key turned on, and shutoff solenoid energized when doing so.

Re: new lift pump made a BIG difference

Reply #15 – December 15, 2014, 06:32:10 pm

Jeff & Sandy,

Whenever any fuel line is opened, including fuel filter changes, air enters. After our new transfer pump (or new prefilled fuel filters), we simply start engine with an immediate high throttle and almost always engine runs fine through hesitations on first try. So we have not used mechanical primp pump for a long time. Years ago we used a long flat narrow board with bottom wedged against frame to push prime pump.

Recently we made a simple modification so we can crank engine without fuel shutoff solenoid opening. We did it to build a little oil pressure before firing, but it probably helps build fuel prime too.

When we changed our fuel lines, we added a ball-valve shutoff at the primary fuel filter to keep fuel from draining back to fuel tank when fuel filters are changed, but don't know if it helped starting after transfer pump.

We have never cracked open an injector line to bleed off air.

We carry many spares, but alternator is not needed as coach can be driven for weeks with generator running, allowing battery charger to supply battery current. Also no need to carry spare fuel shutoff solenoid as a wire tie will keep fuel flowing and cutting wire tie will shut down engine. We have done both of the above for extended times until we could get problems repaired, including accelerating with rope pull.

We installed our Aero resonator two years ago and noticed an immediate power improvement. When we changed to tow vehicle that was over a 1,000 pounds heavier, we noticed it, and the Aero gave us back our mojo. The Aero is a straight through resonator without any sound absorbing material, so I wonder if your straight pipe sounds louder or throatier. We understand why you are happy you got rid of the original muffler.

We are continuing to drive west to Yuma and every day we continue to be fully aware that we have more power on up-hills and start-off from stop that must be from our new transfer pump. Installing a dash fuel pressure gauge gives us new information.

Some have said that fuel priming with ignition on to open fuel shutoff solenoid helps, but that cannot be true. Ignition powers a "hold" coil in the shutoff solenoid, but will not open the solenoid. A "pull-up" coil in the solenoid is temporarily energized when starter is cranked to open solenoid.

Glad you are participating in the Foreforums sharing your American Eagle experiences, Jeff.

Re: new lift pump made a BIG difference

Reply #16 – December 15, 2014, 08:18:04 pm

Barry,

What fuel pressures are you seeing under various conditions, such as idle, high idle, WOT, min-max, etc?

Re: new lift pump made a BIG difference

Reply #17 – December 16, 2014, 12:32:39 am

Robert,

Fuel pressure readout is about 6 to 16 psi. Engine RPM is the main driving force of the range, but it also seems to change a little while driving at about the same RPM. Flow rate seems that it would be a better indication than psi to be sure enough fuel is being fed to injector pump.

We had read that it should be 35 to 45 psi at 1200 rpm, but we are nowhere near that range. I am not sure why the pressure has to be that high as it seems that even 6 psi indicates that the injector pump is not running out of fuel to feed to injectors.

Assuming our new transfer pump is putting out the volume, our low readings seem to say that fuel is flowing back to tank without stressing injector pump. Higher readings are really a measurement of the return valve.

We did purchase a new adjustable fuel return valve that goes on the back side of the injector pump, but have not installed it yet. Partly to first check out the new transfer pump and also because of installation difficulty and the unknowns of what is the best psi.

Re: new lift pump made a BIG difference

Reply #18 – December 16, 2014, 08:59:22 am

Quote from: Barry & Cindy – December 16, 2014, 12:32:39 am

Robert,

Fuel pressure readout is about 6 to 16 psi. Engine RPM is the main driving force of the range, but it also seems to change a little while driving at about the same RPM. Flow rate seems that it would be a better indication than psi to be sure enough fuel is being fed to injector pump.

We had read that it should be 35 to 45 psi at 1200 rpm, but we are nowhere near that range. I am not sure why the pressure has to be that high as it seems that even 6 psi indicates that the injector pump is not running out of fuel to feed to injectors.

Assuming our new transfer pump is putting out the volume, our low readings seem to say that fuel is flowing back to tank without stressing injector pump. Higher readings are really a measurement of the return valve.

We did purchase a new adjustable fuel return valve that goes on the back side of the injector pump, but have not installed it yet. Partly to first check out the new transfer pump and also because of installation difficulty and the unknowns of what is the best psi.

Well, the P7100 is a positive displacement pump so flow will be the same as long as there is a sufficient charge of fuel available, output pressure is what changes. What is important is that the pistons in the pump are charged with fuel from the gallery at the proper pressure. I'd check factory specs and go with that. I've heard mixed opinions on the adjustable banjo bolt check valves, reading between the lines the standard Bosch in good shape seems like the safest option. My limited understanding.

Regarding key on while priming, I agree, it wouldn't make a difference. Could be I turned it on and bumped the engine, could be it was just the effectiveness of the new pump primer, don't remember.

Re: new lift pump made a BIG difference

Reply #19 – December 16, 2014, 10:53:56 am

Chuck, Always bumping the engine would be a good idea for priming. Also it would not take much to put voltage on the pull-up coil without bumping if one wanted to not crank engine to get fuel flowing. Thanks for clarifying.

I need to learn more about proper transfer pump pressure for optimal injector pump operation. I can see there is a tradeoff between too much pressure stressing transfer & injector pump and not enough pressure degrading engine power.

I think the adjustable check return check valve would be a a good thing to install as the original one must be worn, but what pressure to set is an issue. And our dash air compressor is in the way for easy wrenching of the valve, and I am not sure the valve R&R will be impeded by the engine head being too close to the top of the valve. So the new return valve will stay in the spare parts box for now.

Re: new lift pump made a BIG difference

Reply #20 – December 16, 2014, 04:26:15 pm

Barry, 50psi max for the P7100 injection pump on our C8.3s according to the Cummins manual that FT included with purchase and other online sources.

If you look it up, you'll notice that FASS makes 45psi pumps specifically for the P7100 equipped Cummins engines. I was talking to the FASS technical support people today and they said that using a 45psi pump will allow you to remove the mechanical lift pump and go straight to the injection pump.

Also, are you saying that your fuel pressure goes up as RPM increases or down?

Re: new lift pump made a BIG difference

Reply #21 – December 16, 2014, 04:29:11 pm

Question for all electric lift pump engine owners (ISC)
Have any of you had to replace this type pump for reasons other than a leak from seal. I am considering getting a spare and maybe change it but would appreciate any feedback
JohnH

Re: new lift pump made a BIG difference

Reply #22 – December 16, 2014, 05:28:49 pm

John, I just last week had the lift pump replaced on my '99 ISC. The pump had no external leaks and no visible signs of a problem. The engine had gotten awfully hard to start and would sometimes die at idle. The technician was sure it was the lift pump even without a visible problem so I let them change it and the difference in engine performance is night and day. The engine starts almost instantly. According to the silverleaf the engine is producing almost 50 more horsepower and 3-4 pounds more boost. Before the new pump horsepower readings would average about 270 under load and pulling hills. It now reads about 330HP.

Nick

Re: new lift pump made a BIG difference

Reply #23 – December 16, 2014, 05:46:57 pm

Nick, this is good thank you and just for clarities sake do you have a # for that pump on invoice?
I gather yours too is the 350hp
JohnH

Re: new lift pump made a BIG difference

Reply #24 – December 16, 2014, 06:11:30 pm

Yeap, ISC350. Cummins part number 4935007 Pump, Fuel Transfer. Pump cost $295.09

Nick

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