Hard to start/Fuel pump Pressure test 2.5L TJ - JeepForum.com
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post #1 of 1 Old 07-27-2010, 02:35 PM Thread Starter
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1997 TJ Wrangler 
Join Date: Jul 2010
Location: Denver
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Hard to start/Fuel pump Pressure test 2.5L TJ

Hello everyone. After weeks of frustration with the lack of info on my particular Jeep in the Haynes manual, and reading a billion post and threads, I thought it would be nice to have it all in one place for us early model 2.5L 4 cyl TJ owners for reference.

Symptoms - Long cranking times. It takes several cranks before the engine actually fires and/or runs.

Possible problems - Leaking fuel injector, bad/leaking fuel pump pressure regulator check valve, bad fuel pump, or bad fuel pump relay.

The problem with the 2.5L is it does not have a test port/schrader valve on the fuel rail.

In order to check diagnose the problem you will need a few specialty tools.

a) Fuel pressure gauge that goes to at least 60 Psi

b) Fuel pressure test adapter #6539 That will go in between the fuel rail and the fuel in-line. found here Miller Tools 6539 Fuel Pressure Test Adapter

c) a fuel line disconnect tool that slides into the fuel in-line connector. Caution, your type of quick connect may or may not be shown in the Haynes book. You can find these at most parts stores. Be sure you get the right disconnect tool. (Mine was not shown in the book and I used a tool made by OEM part #27131 found at autozone)

Here are a few previously posted responses that will help you diagnose the problem:

Use following procedure if the fuel injector rail is not equipped with a fuel pressure test port.

(1) Remove fuel fill cap.
(2) Remove fuel pump relay from Power Distribution Center (PDC). For location of relay, refer to label on underside of PDC cover.
(3) Start and run engine until it stalls.
(4) Attempt restarting engine until it will no longer run.
(5) Turn ignition key to OFF position.

CAUTION: Steps 1, 2, 3 and 4 must be performed to
relieve high pressure fuel from within fuel rail.

In order to test fuel where there is no valve on the fuel line you need to use an adapter that fits between the fuel line and the fuel rail using the quick release fitting there.(adapter #6539) The volume test requires using an adapter hose to fill a graduated container with fuel. The pump should be operated for a maximum of seven seconds, and it should pump at least a quarter liter of fuel in that time.

NOTE: The fuel pressure test port is used on certain engines only. If equipped, the test port will be located on the fuel rail . If not equipped, refer to the following procedure :

All fuel systems are equipped with a fuel tank module mounted, combination fuel filter/fuel pressure regulator. The fuel pressure regulator is not controlled
by engine vacuum.

With engine at idle speed, system fuel pressure should be 338 kPa 5 kPa (49.0 psi 2 psi).


(1) Release fuel pressure. Refer to the Fuel System Pressure Release Procedure.
(2) Disconnect latch clip and fuel line at fuel rail. Refer to Quick-Connect Fittings for procedures. This can be found in this section of the group.
(3) Connect adapter tool number 6539 or 6631 into fuel rail. Be sure adapter tool is fully seated into fuel rail.
(4) Install latch clip to fuel rail. If latch clip can not be fully seated into fuel rail, check for adapter tool not fully seated to fuel rail.
(5) Connect vehicle fuel line into adapter tool. Be sure fuel line is fully seated into adapter tool.
(6) Remove protective cap at test port "T" on adapter tool.
(7) Connect the 0-414 kPa (0-60 psi) fuel pressure gauge (from gauge set 5069) to the test port "T".
(8) Start engine and note pressure gauge reading. Fuel pressure should be 338 kPa 5 kPa (49.0 psi 2 psi) at idle.
(9) If pressure is at 0 psi, connect DRB scan tool and refer to the appropriate Powertrain Diagnostics Procedures service manual.
(10) If operating pressure is above 51 .0 psi, fuel pump is OK but pressure regulator is defective. Replace fuel filter/fuel pressure regulator assembly.
(11) After performing pressure test, install fuel line into fuel rail. Install latch clip into fuel rail. Refer to Quick-Connect Fittings in the Removal/Installation
section of this group for procedures.

Before performing this test, verify fuel pump pressure by performing the Fuel Pump Pressure Test. Use this test in conjunction with the Fuel Pressure Leak Down Test found elsewhere in this group.
(1) Release fuel system pressure. Refer to the Fuel Pressure Release Procedure in this group.
(2) Disconnect fuel supply line at fuel rail. Refer to Quick-Connect Fittings in the Service Procedures section of this group for procedures. Some engines
may require air cleaner housing removal before line disconnection.
(3) Connect appropriate Fuel Line Pressure Test Adapter Tool Hose (number 6631, 6923, 6541 or 6539) into disconnected fuel supply line. Insert other
end of Adaptor Tool hose into a graduated container.
(4) Remove fuel fill cap.
(5) To activate fuel pump and pressurize system, obtain DRB scan tool and actuate ASD Fuel System Test.
(6) A good fuel pump will deliver at least 1/4 liter of fuel in 7 seconds. Do not operate fuel pump for longer than 7 seconds with fuel line disconnected as
fuel pump module reservoir may run empty.
(a) If capacity is lower than specification, but fuel pump can be heard operating through fuel fill cap opening, check for a kinked/damaged fuel supply line somewhere between fuel rail and fuel
pump module.

(b) If line is not kinked/damaged, and fuel pressure is OK, but capacity is low, replace fuel filter/fuel pressure regulator. The filter/regulator may be
serviced separately on certain applications. Refer to Fuel Filter/Fuel Pressure Regulator Removal/Installation for additional information.
(c) If both fuel pressure and capacity are low, replace fuel pump module assembly. Refer to Fuel Pump Module Removal/Installation.

Use this test in conjunction with the Fuel Pump Pressure Test and Fuel Pump Capacity Test.

Check Valve Operation: The electric fuel pump outlet contains a one-way check valve to prevent fuel flow back into the tank and to maintain fuel supply line pressure (engine warm) when pump is not operational. It is also used to keep the fuel supply line full of gasoline when pump is not operational. After the vehicle has cooled down, fuel pressure may drop
to 0 psi (cold fluid contracts), but liquid gasoline will remain in fuel supply line between the check valve and fuel injectors. Fuel pressure that has dropped to 0 psi on a cooled down vehicle (engine off) is a normal condition. When the electric fuel pump is activated, fuel pressure should immediately (12 seconds) rise to specification. Abnormally long periods of cranking to restart a
hot engine that has been shut down for a short period of time may be caused by:
Fuel pressure bleeding past a fuel injector(s).
Fuel pressure bleeding past the check valve in
the fuel pump module.

Testing for fuel pump check valve, filter/regulator check valve or fuel tube/line leakage:

Clamp off the rubber hose portion of Adaptor Tool between the vehicle fuel line and test port T on Adapter Tool. If pressure now holds at or above 30
psi, a leak may be found at a fuel tube/line. If no leaks are found at fuel tubes or lines, one of the check valves in either the electric fuel pump or filter/regulator may be leaking.

Note: A quick loss of pressure usually indicates a
defective check valve in the filter/regulator. A slow
loss of pressure usually indicates a defective check
valve in the electric fuel pump.

The electric fuel pump is not serviced separately. Replace the fuel pump module assembly. The filter/regulator may be replaced separately on certain applications. Refer to Fuel Filter/Fuel Pressure Regulator Removal/Installation for additional information.

I hope this helps and if anyone has anything to add, please feel free. Once you get all the right tools the test itself is very easy.

Beamish17 is offline  

fuel pump , pressure test , write-up , write up , help , tj , wrangler , 2.5

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