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OnlineHelp, Mechanic
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Experience:  Mechanic
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I have a 1995 Jeep Grand Cherokee 4.0l inline 6 cyl with ...

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I have a 1995 Jeep Grand Cherokee 4.0l inline 6 cyl with almost 200 000 miles. When the car is cold it runs great,   toward the afternoon, when hot, it starts to splutter like there is air in the fuel line. I have replaced plugs, wires, distributor cap, map sensor, and control module under steering wheel ( left hand side attached to fire wall) When this problem occurs, i can floor the gas pedal and nothing happens, the car starves of fuel and backfires. I tested the fuel pump, and the pressures are within range, and I also replaced the inline filter. Could this be a problem with my muffler or Catalytic converter being blocked or possibly a bad oxygen sensor. What do you suggest other than a burial plot.
Submitted: 8 years ago.
Category: Car
Expert:  OnlineHelp replied 8 years ago.

Hello and thank you for choosing Just Answer.

Backfires indicated a bad air/fuel mixture. There are couple of things that will cause this. You should start with the basics.

  • Check air filter
  • Check for vacuum leaks
  • Check firing order
  • 1995 Jeep Grand Cherokee 2WD
    4.0 liter L6 VIN "S"

However the main test that you want to do here is going to be a fuel pressure test at the rails. This will not only test the pump, but also the fuel pressure regulator. Also make sure all you injectores are working, if you put a screw driver on a fuel injector you should feel a ticking.

You can chec if a muffler or catalytic converter is clogged by hitting them from the bottom. You should hear a rattle in them. You can also take off a oxygen sensors and flow air through, this test is a lot better, there should be no restriction when you blow air through the oxygen sensor mounting hole.

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