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Several things that could cause misfires:
  • Is the misfire occurring on any particular cylinder? What brand of spark plugs are you using? You should be using OEM NGK plugs; other brands such as Champion or Bosch many times cause driveability problems in Nissan engines.
  • Dirty fuel injector(s). Run some good injection cleaner, like BG products 44K, through the system; give the cleaner about a week or two to do it's job.
  • Incorrect fuel pressure. Tee-in a temporary fuel pressure gauge between the fuel feed hose and the fuel rail. The readings at idle should be 51psi
  • Leaking fuel injector(s). A good way to test for leaking fuel injectors is to Tee-in a temporary fuel pressure gauge between the fuel feed hose and the fuel rail. Turn the ignition key to the run position but DO NOT TRY TO START THE ENGINE; wait 10 seconds, then turn the ignition key to OFF. The fuel pressure reading should be around 51psi which would be a static reading. Now watch the gauge; if it starts dropping down fast, that's an indication of a fuel injector(s) leak.
  • Bad coil pack. Did you replace just one coil pack or all of them.
  • The cam position sensor may be marginal.
  • There may be a major intake system vacuum leak. To check the intake system for a vacuum leak, attach a vacuum gauge to a full vacuum source. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be 21 InHg. If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.
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