Diesel Lift Pump

Diesel Lift Pump

The Cummins Lift Pump

     CUMMINS FUEL SYSTEM

                       The Cummins Lift Pump

 

This article is number one in a six part series on the Cummins fuel system (1994 to 1998 equipped with the P pump). This applies to the Cummins 5.9 and 8.3 diesel, as they share the same lift and injection pump. During the prototype stage of designing new products for the P7100 and the Cummins fuel system, we completed hundreds of tests and thought it was necessary to share this information with diesel owners and Cummins performance enthusiasts.
 
 

THE BOSCH P7100 IS THE KING OF INJECTION PUMPS

 

 
The Cummins 12 valve enjoys incredible popularity because of its simplicity, durability, ease of maintenance and the low purchase price of the truck. Power increases are about as cheap as they get, without the complexity of electronics and fault codes. Power levels in the 400 HP+ range are not uncommon for the Cummns 12 valve, and it can still be driven on the street! The Bosch P7100 (P Pump) is the king in sled pulling competition. Several of these torque monsters exceed 1000 horsepower on only 5.9 liters !!
 
Let's dig in with some interesting comparisons on the lift pump. The Carter lift pump is a basic hydraulic piston pump. Industrial piston pumps are typically made from high strength castings while the lift pump body is made from an aluminum die casting. Piston pumps rarely use check valves, while our Cummins transfer pump uses three. The piston on a hydraulic piston pump is connected to the swash plate by a connecting rod or with the use of a ball and socket design. The piston in the Cummins lift pump is actuated by a plunger, while the return stroke is by spring pressure. Hydraulic piston pumps have precision ground cylinders and pistons. Our lift pump doesn't share any of the features of industrial pumps, but it is still is a time tested design.
 

  THE PEAK FUEL FLOW NUMBER AND IT'S NOT GOOD

 

In spite of its draw backs, the lift pump is very reliable! My 98 has 376,000 on the original Cummins lift pump. Unlike its industrial cousin, our lift pump is only 35% efficient at rated RPM. For all of the tests, rated RPM is 2500. 35% is INCEDIBLY LOW, and by the end of article number two, you will know why. With that knowledge in hand, you will be able to increase the efficiency of your system and make HP improvements more easily.
 
Let's start with a few specs on the Carter lift pump (aka the Cummins lift pump). During the development stage of our fuel products, we collected a large amount of information on the lift pump from shop manuals, diesel forums, and we requested additional information from the manufacturer. Cummins rates the pump at 52.8 GPH (gallons per hour). 52.8 divided by 60 equals .88 GPM. To be candid, the rated and actual flow ratings were very different.

Normally a piston pump's flow will increase, to a point, as RPM increases (in a well designed system). Not so with the lift pump. The numbers go down after 2200 RPM. I will explain in detail WHY this takes place, in article number two. Some of you may be thinking that the lift pump is bad because the efficiency is so low. We tested all GPM flows with a brand new lift pump and fuel filter. There were no visible air bubbles in the clear hoses leading to and from the flow meter. 35% efficiency is a very low number and we will explain why.
 
As mentioned above, we have made several hundred tests using precise flow meters and accurate pressure gauges. Sometimes our assumptions were very close and other times the readings didn't make sense. The findings that didn't match hydraulic principles, forced us to dig deep to find out why. Remember, one good test is equal to a thousand expert opinions.

SOME BASICS ON THE LIFT PUMP

 

Contrary to popular belief, the Cummins lift pump produces flow on the return stroke of the piston, not the forward stroke. Spring pressure on the return stroke, NOT the forward plunger movement, is what produces the flow in the fuel system. In article number two, you will discover why you cannot efficiently run your fuel pressure higher than 32 PSI.

HOW DO WE FIND THE PUMPS DISPLACEMENT?

 

 

How do we determine the calculated displacement of this pump. Here is a handy formula to determine cubic inch displacement of any cylinder (pump) or engine. This formula is easy and works great for finding the cubic inch displacement of your engine or any piston pump. Bore x bore x stroke x .7854 x number of cylinders = displacement in cubic inches.

1.180 x 1.180 x .25 x .7854 (constant) x 1 = .273 in³.

For every stroke of the piston, it should produce aproximetely 1/4 cubic inch of fuel flow.

 

EASY FORMULA TO CALCULATE GPM

We now know that our lift pump displaces .273 cubic inches. How do we figure the calculated GPM flow of the lift pump? The formula is very easy.  .273 in³ x pumping cycles per minute (remember that the pump is at half speed of the crank) divided by 231 (cubic inches per gallon of water) = GPM.

.273 x 1250 (half speed of 2500 rated RPM) = 341 divided by 231 = 1.477 GPM. The carter lift pump is calculated at 1.477 (rounded up to 1.48) GPM at 100% efficiency.
 

AND NOW THE GOOD STUFF!

 

This photo shows the GPM flow at idle, which is 800 RPM. We are now going to use the formulas. Please bear with me, it's straight forward, and rather easy.  .3 GPM meter reading x 1.0495 = .315 corrected GPM. This is the actual flow from the Carter lift pump at idle. What is the calculated flow of this piston pump? 400(half engine speed) x .273 cubic inches = 109. 109 divided by 231 (cubic inches in a gallon) = .47 GPM. At 100% efficiency, our lift pump should flow .47 GPM. So, we now take .315 (actual flow) divided by .47 (calculated) = .67 or 67% efficient. Not the best efficiency number, but OK.

This is the GPM flow at 1500 RPM. My apologies for the faint image.  .4 x 1.0495 equals .42 GPM. If this pump were 100% efficient, it would flow .89 GPM. At 1500 RPM our Cummins transfer pump is only 47% efficient. .42 (actual) divided by .89 (calculated GPM flow) = .47 or 47%. Are you starting to see a trend? As the RPM increases, the efficiency goes down !!

THE NUMBERS GET WORSE !

 

 

At 2500 RPM, we are flowing .52 GPM (.5 x 1.0495 correction) At 2500 RPM, the efficiency has dropped to 35%. That's .07 GPM less than at 2200 RPM.  We reached peak flow of .59 GPM at 2200 and everything thereafter is going down hill. If you installed a 4000 RPM governer in your P pump, your fuel flow is in the neighborhood of .44 GPM. My mathematition son, Curtis, arrived at this number by using calculus.

So, our Cummins lift pump is capable of flowing 1.48 gallons per minute of diesel fuel at 2500 RPM. I'm here to tell you that the Carter lift pump is no way near its calculated GPM flow of 1.48. Not even close!! The Carter lift pump only flows .52 GPM at 2500 RPM. That equates to ONLY 35% efficiency. It flows .59 GPM at 2200 RPM, which is 45% efficient. To calculate efficiency take the actual GPM divided by calculated GPM.  

.59 divided by 1.3 GPM = .45 or 45% efficient. That's at peak fuel flow. At rated RPM it's much worse!

OUR LIFT PUMP NEEDS HELP!

800 RPM           .315 Actual GPM       .47 Calculated GPM           67% Efficiency
1500 RPM         .42 Actual GPM         .89 Calcualted GPM           47% Efficiency    
2200 RPM              .59 Actual GPM          1.3 Calculated GPM           45% Efficiency
2500 RPM              .52 Actual GPM          1.48 Calculated GPM         35% Efficiency  
  
The following numbers were arrived at by using calculus.

4000 RPM         .44 GPM                   2.36 Calculated GPM         18.6% Efficiency

From an industrial point of view, this lift pump would have to be replaced with a better, more efficient design. Industrial piston pumps are a minimum of 85% efficient. Some models are 90 to 95% efficient. There are several reasons why the efficiency of the Cummins lift pump is so low and it's not the pump's fault !! The secrets on how to improve your fuel system will be revealed in article number two.

When the fuel system on the 94 to 98 Dodge Cummins was designed, they failed to follow basic hydraulic principles. This failure (or intended design to limit HP) is the reason why the lift pump only flows 35% of it's capability at 2500 RPM.

We will cover the reasons why the efficiency goes down as the RPM goes up, and what can be done about it, in article number two. New articles will be published about every 2 weeks. If you want to subscribe to the series of articles, drop me a line at robsr@torkteknology.com and I will send the series to you FREE of charge. When i say free, that's exactly what I mean! This information series is intended to provide accurate and tested information to the diesel community.

Rob Parelli Sr
Torkteknology.com

About the Author

I operate Tork Teknology, a company that specializes in finding solutions to the pickup diesel market. We made hundreds of tests and we want to share the knowledge.

BD Diesel Lift Pump Kit;Type Of Kit $270.99 BD Diesel Lift Pump Kit;Type Of Kit: Bypass

BD Diesel Intank Pump Retrofit Kit 1050302 $10.99 Required for installation of Flow-MaX Lift Pumps on 1998.5-2004 BD Diesel Dodge 5.9L trucks that have had the OEM BD Diesel Intank lift pump conversion done to it.

BD Diesel FlowMax Lift Pump Kit $470.99 Full Flow Rating:165gph;Pump Design:Gerotor

BD Diesel Lift Pump Kit $280.99 Auxiliary;

BD Diesel Fuel Pressure Kit $179.99 Option for: BD Diesel X-Monitor;Sender for:Lift Pump Fuel Pressure

Diesel Women's Passion Pump $249.95 Diesel Women's Passion Pump

2003-2004 Dodge Ram 2500 Fuel Pump BD Diesel Dodge Fuel Pump 1050227 03 04 $277.45 BD DIESEL LIFT PUMP KIT, NEW -- Electric; Includes all necessary hoses and mounting hardware; A high quality, direct fit lift pump kit; Designed to deliver ample fuel flow for more than 600 h.p.; Easy installation.. Auto Parts Warehouse has extensive BD Diesel Fuel Pump catalogs.We are now offering FREE shipping on all BD Diesel Fuel Pump orders over $50.00. Our secure bd diesel fuel pump catalog is available every hour of everyday. Shop with confidence for all your bd diesel fuel pump needs. BD Diesel Fuel Pump are In Stock and available today. Save up to 60% off dealer price on your next BD Diesel Fuel Pump purchase. Our online catalog contains a wide selection of the OEM and aftermarket parts you need at unbeatable prices

Diesel Women's Ex-Cute Pump $144.95 Diesel Women's Ex-Cute Pump

Diesel Women's Lacy-Trek Pump $179.95 Diesel Women's Lacy-Trek Pump

1998-2007 Dodge Ram 2500 Fuel Pump BD Diesel Dodge Fuel Pump 1050226 $262.82 bd diesel auxiliary lift pump kit new electric includes wiring harness and mounting hardware designed to deliver ample fuel flow for more than 600 h.p. features bd diesel s proprietary switch solves hard start issues common with other lift pump kit adds a proven second lift pump to extend the life of the fuel system easy installation auto parts warehouse has extensive bd diesel fuel pump catalogs.we are now offering free shipping on all bd diesel fuel pump orders over $50.00. our secure bd diesel fuel pump catalog is available every hour of everyday. shop with confidence for all your bd diesel fuel pump needs. bd diesel fuel pump are in stock and available today. save upto 60% off dealer price on your next bd diesel fuel pump purchase. our online catalog contains a wide selection of the oem and aftermarket parts you need at unbeatable prices

Diesel Fuel Injection Pump Testing $24.99 Heinz Zinran Diesel Fuel Injection Pump Testing - Photographic Print

BD Diesel Flow-MaX Fuel Lift Pump Kit $541.99 Incl. Hoses/ Mounting Hardware;