A fuel injector on an Infiniti Q45 can cause a misfire as easily as a spark plug or other problem in the ignition system can. In the past, the cylinders depended on the collective shared fuel mixture within the intake manifold for the fuel charge. The introduction of the TBI fuel injection system, which uses one or more fuel injectors within a throttle body act, for the most part, just like a carburetor, except the engine has better throttle response and an evener mixture as it is not vacuum-dependent. The computer compensates for air density and altitude. The multi-port fuel injection, as is found on the Infiniti Q45, is a completely different animal. The intake manifold is comprised of air and each cylinder is dependent on its individual fuel injector.
Determine which cylinder affected by starting the engine and allowing it to reach operating temperature. Use the infrared thermometer to check the temperature at each cylinder at the point the exhaust manifold is bolted to the cylinder. If all cylinders are averaging 450 degrees except one (it is much lower), this is the cylinder in question.
Use the engine stethoscope or fuel hose against the ear to listen to the fuel injector, which should be making a steady clicking noise as it operates. If no noise is detected the electrical connector should be checked for power or broken or chaffed lines. If a steady noise is present, it could be stuck open somewhat or have a dirty pintle.
Disconnect the electrical connector on the fuel injector with the engine running. Use the small pocket screwdriver to unsnap the lock spring on the connector and pull the connector off. While the connector is removed, notice the amount of drop in engine rpm. Push the connector on and then pull it off to verify its functioning. If no engine drop is noticed the internal filter could be completely clogged and may be able to be cleaned with a fuel injector cleaner. It could also be totally defective, which is what must now be determined.
Install the noid light in the electrical connector to the injector. The noid light should be blinking rapidly. If it is not blinking, check the connector with a voltmeter to see if one of the terminals has power. If there is power at one of the terminals, the problem lies within the computer injector driver circuit. It needs a computer. If there is no power to the connector, there is a broken wire between the fuse block and the injector--most likely in the harness. If the noid light is blinking and the injector is making a clicking noise, flush the injectors with a professional fuel injector cleaner. If the injector still malfunctions, replace it.
Shut the engine down and allow it to cool. Pull the spark plug from the affected cylinder and look at the electrode. If it is crusty black in color, the injector is stuck open and should be replaced because it is highly unlikely it can be cleaned. If the electrode is white or light gray with a scorched look, the injector is not opening properly and may be able to be cleaned. Replace only if it continues to malfunction.
