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Donny
Donny, Shop Foreman
Category: Jeep
Satisfied Customers: 828
Experience:  A.S.E. Certified A1-A8,L1,X1,T1,T2 Over 25 years Experience with Chrysler - Dodge - Jeep
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1995 Jeep Grand Cherokee 4.0 engine -- skipping, popping, ...

Customer Question

1995 Jeep Grand Cherokee 4.0 engine -- skipping, popping, won''t idle, hard to start. Thought it was the engine, replaced but it is still doing the same thing.
Submitted: 6 years ago.
Category: Jeep
Expert:  Donny replied 6 years ago.

Hello

lets start by verifying the fuel system

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

With engine at idle speed, system fuel pressure should be 49.0 psi ± 2 psi

WARNING: DO NOT ALLOW FUEL TO SPILL ONTO THE ENGINE INTAKE OR EXHAUST MANIFOLDS. PLACE SHOP TOWELS UNDER AND AROUND THE PRESSURE PORT TO ABSORB FUEL.

WARNING: WEAR PROPER EYE PROTECTION WHEN TESTING FUEL SYSTEM PRESSURE.

  1. Remove the protective cap at the fuel rail test port. 0-60 psi fuel pressure gage to the test port pressure fitting on the fuel rail.
  2. Start the engine and note pressure gauge reading. Fuel pressure should be 49.0 psi ± 2 psi at idle.
  3. If operating pressure is above 51.0 psi, fuel pump is OK but pressure regulator is defective. Regulator is not serviced separately. Replace fuel pump module assembly.

Before performing this test, verify fuel pump pressure by performing the previous tests.

  1. Release the fuel system pressure from fuel system.
  2. Disconnect the fuel supply line at the fuel rail. Refer to Fuel Tubes/Lines/Hoses and Clamps in this section of the group for procedures. Some engines may require air cleaner housing removal before line disconnection.
  3. Connect the appropriate Fuel Line Pressure Test Adapter Tool into the disconnected fuel supply line. Insert the other end of Adapter Tool into an approved gasoline container.
  4. activate the fuel pump and pressurize the system.
  5. A good fuel pump will deliver at least 1 liter of fuel per minute. If not replace the pump

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.
  1. Disconnect the fuel inlet line at fuel rail. . On some engines, air cleaner housing removal may be necessary before fuel line disconnection.
  2. Connect the appropriate Fuel Line Pressure Test Adapter Tool between the disconnected fuel line and fuel rail
  3. Connect a 0-60 psi fuel pressure test gauge to the test port on the appropriate Adapter Tool. The fittings on both tools must be in good condition and free from any small leaks before performing the proceeding test.
  4. Start engine and bring to normal operating temperature.
  5. Observe test gauge. Normal operating pressure should be 49 psi ± 2 psi
  6. Shut engine off.
  7. Pressure should not fall below 24 psi for five minutes.
  8. If pressure falls below 24 psi, it must determined if a fuel injector, the fuel pressure regulator or a fuel tube/line is leaking.
  9. Again, start engine and bring to normal operating temperature.
  10. Shut engine off.
  11. Checking for fuel injector leakage: Clamp off the rubber hose portion of Adapter Tool between the fuel rail and the test port "T" on Adapter Tool. If pressure now holds at or above 24 psi, a fuel injector or the fuel rail is leaking.
  12. Checking for fuel pump module or fuel tube/line leakage: Clamp off the rubber hose portion of Adapter Tool between the vehicle fuel line and test port "T" on Adapter Tool. If pressure now holds at or above 24 psi, a leak can be found at a fuel tube/line. If no leaks are found at fuel tubes or lines, replace the fuel pump module.

Let me know how you make out with this and we can move on to more testing if needed

Thank you

Donny

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