Frequently Asked Questions (FAQ)

Do the FASS Diesel Fuel System kits include everything needed to install them? What about Class 8 kits?

The majority of FASS Diesel Fuel Systems are vehicle specific and come with all parts needed for installation. The Class 8 kits require a fuel return line kit to complete installation (visit to see the complete line of fuel line kits).

I have purchased one of your diesel fuel systems, how do I receive the extended warranty?

After purchasing your fuel system from a registered or authorized FASS dealer it’s essential to complete the 1st page (front and back) of the installation manual within 30 days and mail to address below with a copy of your receipt or visit to register online.

Diesel Performance Products, Inc.
16240 Hwy O Suite B
Marthasville, MO 63357

Can I install the FASS Diesel Fuel System myself or does it need to be installed by an authorized FASS installer?

FASS is continuously updating and changing our fuel systems to make them easier to install for the end user. As long as you take your time, read and follow the provided installation manual, installs can be completed by the end user. If you have any questions, please don’t hesitate to call our staff of knowledgeable customer service representatives.

Will my fuel mileage increase?

After the installation of the Titanium Series FASS Diesel Fuel System, our customers have reported 2-3 mpg increases for pickups and .4 mpg increases for Class 8. While this is an average, FASS cannot guarantee fuel mileage increases.

Am I required to use FASS filters on the Titanium series unit?

FASS realizes that in emergency situations you may not be able to find FASS filters in time. For your convenience, at, we have provided a list of cross reference filters available at auto parts stores and full service truck stops

Does FASS void factory manufacturer warranties?

No, FASS Diesel Fuel Systems do not void factory manufacturer warranties, because our products meet or exceed OEM filter specifications.

What pressure should my pump be running at?

  • Duramax engines 8-10 psi
  • Cummins engines
  1. ’89-’93 6-8 psi
  2. ’94-’98 16-18 psi when supplying factory lift pump.
  3. ’94-’98 45 psi when supplying directly to P-7100
  4. ’98.5-present 16-18 psi
  • Ford Powerstroke
  1. ’99-’07 55 psi
  2. ’08-’10 8-10 psi
  3. ’11-present 55 psi
  • Majority of class 8 units will be preset at 16-18 psi

What fuel filters do I need for my unit?

  1. HD Series
  2. Titanium Series (Gun Metal Grey Color)
  3. Titanium Series (Old Style Blue Color)
  4. Platinum Series
  • NOTE**All 95/Titanium Series units with a FF-2003 fuel filter will need P/N FSN-2001 installed in order to use the FWS-3003/cross reference.

I just changed my fuel filters, how do I prime my unit?

    • Click below to watch “How to Prime a FASS Diesel Fuel System” instructional video:

My pump no longer turns on when the key is turned to the run position, what’s wrong?

  • Check for a blown fuse in the FASS wire harness
  • Using a multimeter, check to make sure relay is working properly. Terminal number 85 should have 12 volts when the key is turned to the run position. On  ’98.5-present Dodge Cummins, the engine will need to be turned over with the starter one revolution to check for 12 volts at terminal 85.
  • Using a multimeter, check for 12 volts at the electrical connection at the FASS unit.

My unit is very loud, what’s wrong?

  • A loud pump can be caused by several issues. Clogged filters will cause the pump to cavitate and become loud. If a restriction is present on the suction side of the fuel pump there will be excessive cavitation which will cause the noise of the pump to increase. Majority of the time a restriction on the suction side of the pump will be a clogged screen on the bottom of the fuel module inside the fuel tank. Excessive pressure could also cause the unit to over amp and become loud. A fuel pressure gauge will be needed to determine the pressure.
  • Click Below to Watch our “5 Gallon Bucket Test” Instructional Video

When my fuel level is below a ¼ tank, I run out of fuel or my fuel pressure drops to 0 psi, why?

If your unit is not equipped with a STK/sump bowl, the factory fuel module supplies the FASS pump. Factory fuel modules are equipped with a filtering screen which, over time, can become clogged by the contaminates found in diesel fuel. When the fuel level starts to go down to ¼ tank and below fuel can’t enter the basket from the top anymore. If the screen is clogged and not allowing fuel to enter, the FASS pump will empty this basket before it can refill causing the truck to run out of fuel.

I have a ’98.5-’02 Dodge Cummins and after the truck has reached operating temperature and I shut the truck off, I have a long crank time before the truck will start again, why?

The VP44 injection pump is equipped with a diaphragm and this diaphragm can develop a crack in it which will allow fuel to seep past it during start up. This issue is not necessarily from high fuel pressure. For testing procedures and solution please refer to page 26 of the troubleshooting guide.

Click Here to view the FASS Technical & Troubleshooting Guide

My truck is stock at this time but I plan to do upgrades in the future, will too large of a pump hurt my truck?

Yes and no. To a point, you can have more flow than you need but you DO NOT want excessive pressure. Many customers choose to purchase a 150gph pump for the stock/mild upgrades because the price difference between the 95gph and 150gph is so little. This is fine as the pressure will still be at the recommended pressure for your vehicle.

Having a pump that is larger than 150gph on a stock or slightly modified truck can cause issues. Vehicles that actually need larger units are mainly purpose-built competition vehicles and can handle higher pressures. Along with other competition specific parts, these pumps are going to be much louder. Performance of the motor will produce added pressure which will create more amp draw and lessen the electric motor life. Please select the FASS Diesel Fuel System for your application. If you aren’t sure which system will suit your application, please give our support team at call at (636) 433-5410, or shoot them an email at!

Click Here for our List of Customer Service Contacts.