In Feb I sent to Nissan wshop for diagnosis, and was told slight lube leak via Rocker cover seals. I got it replaced. Right after service, I went to another wshop to fix the exhaust system. The rear muffler/silencer pipe have the hole repaired, and was also advised to remove the Catalytic Converter as it only cause back pressure, I got it removed. But after a week, the problem comes back. Two weeks ago, I went back to Nissan wshop, they checked and says no problem with ignition system, but could be the exhaust system. Does removing the Catalytic converter has any relation of this intermittent momentary loss of engine power? It happens during idling and also while on the move.
My car has 186700 miles.
My car has an automatic transmission.
The catalytic converter does help to contribute to back pressure, however, it may not be related to your loss of power issue. If the same issue existed before removing the catalytic converter, then it is likely not the problem.
Intermittent loss of power could very well be a fuel delivery or ignition problem. Since the ignition problem was ruled out by Nissan, I would recommend checking the various fuel/air monitoring sensors such as the mass air flow sensor and throttle position sensor.
The mass air flow sensor regulates the air coming into the engine allowing it to mix with the fuel properly before being injected into the engine. When this is faulty, it will cause intermittent loss of power as you describe due to its inability to properly mix the air and fuel which causes the car to starve for fuel.
The throttle position sensor can also cause this same problem when it is faulty, as it monitors the position of your foot on the gas pedal and tells the car's fuel injection system how much fuel to give the engine.
If you would like to have this scoped out by another technician, a certified professional from YourMechanic can come to your home or office to diagnose the power loss problem firsthand.
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