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High pressure Fuel Leak Test

The high pressure fuel pump supplies high pressure fuel as high as 300-1800BAR or 4351-26107 PSI to each injector through the high pressure lines.
Fuel under this amount of pressure can penetrate the skin and cause personal injury or death.
Wear safety goggles and adequate protective clothing and avoid contact with fuel spray when checking high pressure lines for leaks.

To perform the leak test start the engine . move a piece of cardboard over the high pressure fuel lines and check for fuel spray onto the cardboard.

If a high pressure connection is leaking shut the engine off and loosen the connection than tighten it to specification.

If the fitting is still leaking turn off the engine remove and inspect the fitting and mating surface and replace as needed.

If the high pressure line is leaking, replace it with a OEM Cummins high pressure line.


The high pressure fuel system can be diagnosed using a scan tool.

the data will show fuel pressure set point and actual fuel pressure

when trouble shooting fuel system issues look for deviations between fuel rail set point and actual pressure

if a small leak is suspected in the high pressure lines check the lines using the cardboard test

Other tests include

high pressure fuel pump flow: tests the ability of the high pressure fuel pump to supply fuel volume. This is a go-no-go test. If fuel is present , further testing is necessary

Fuel pressure limiting valve test:test the ability of the FPLV to maintain pressure if fuel leaks are detected the FPLV must be replaced

Injector return flow test:test the injectors and high pressure fuel transfer tubes for leaks. excessive fuel return flow indicates a concern each cylinder must be isolated until concern is identified and corrected after repairs return flow must be retested to verify no additional concerns exist

Fuel pump return flow test:Measures the ability of the high pressure fuel pump to provide specified return fuel volume.

when working on the 6.7L fuel lines it is tempting to bend the lines out of the way to get at items or tube nuts. Remember that the rigidity and internal dimensions of those lines is crucial to proper engine operation

you can check the fuel line from the tank to the connection at the frame rail near the firewall area for small cracks or leaks

disconnect the supply line as close to the tank module as possible and plug the line.

go to the connection on the frame rail close to the firewall and use a hand held pump to apply not more than 15-20 inches of mercury to the line.

the vacuum should not drop more than 0.1 in hg per minute.

test the system for a minimum of 5 minutes you can also check the system from the frame rail point to the high pressure pump the same way.


engine must be at operating temperature or at least above 180F

install a test fitting into fuel drain tube banjo on the rear of the filter assembly (Chrysler number 9012) will also need fuel block off cap Chrysler number 9011

disconnect the vehicle return line from the filter return line on the filter assembly install a hose onto the test fitting and place the end into a catch can

install a hose onto the filter return line end that is now open and route the hose end into a graduated cylinder for measuring injector return flow

run the engine for one minute and measure the amount of fuel in the measuring device

if the amount collected is less than 180ml with the engine off re-torque all of the high pressure connector fittings including the transfer tubes re-measure the fuel return

if the amount is still more than 180ml cap off each injector until the suspect injector id located


this test is used for a vehicle that has a no start condition

this test is similar to the test above with the following exceptions

*unplug the injector harness connector at the valve cover and FCA connector during testing

*measure the fuel return flow during a 10 second cranking test

*make sure the key is returned to the "key off" position immediately after the 10 second crank time

*the amount measured should be less than 40ml for 10 seconds of cranking

*if not cap off the injectors one at a time until the suspect injector is found

*it is possible to have more than one injector failure on the same engine remember to clear codes after testing


make sure the tank contains at least 1/4 tank of fuel the lift pump can draw air into the lines if this minimum is not met

*check the system lines for leaks or damage

*check battery voltage that is at least 11.5 volts

*remove the fuel feed line at the high pressure pump this is the low pressure line coming out of the filter attach a hose to the line from the fuel filter and insert the other end into a graduated cylinder for measuring

*using a scan tool activate the fuel pump for 10 seconds and check how much fuel has been caught in the graduated cylinder

there should be 570ml of fuel in the graduated cylinder after the 10 second pump test perform 3-10 second tests and take the average of all three to use as your result

if the test fails check the banjo bolt at the fuel filter outlet line and make sure the screen is free of debris

if no debris is found change the fuel filter and re-test

anytime repairs are made make sure to bleed air from the system before re-testing

if the specification is still not met remove the in tank lift pump and inspect repair or replace


the high pressure common rail engine has a cascade overflow valve located on the high pressure pump it is the furthest away from the engine on top of the pump

to check the valve clean the area around the valve to ensure no debris enters the pump during removal remove the valve and inspect for blockage damage or debris using a small pin punch or pen tip check the movement of the valve plunger when checking make sure the valve plunger returns to the static state if the plunger does not return most likely the spring is broken replace the cascade overflow valve

when replacing the valve or re-installing the old valve replace the o-ring and lubricate with clean diesel fuel install the valve and torque to 5 ft lbs run the engine and check for leaks
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