Q: Lack of power 1991 Nissan 300ZX

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I replaced my engine bc my car was losing power with the last engine I pulled out and when I put in the new engine there was a mis fire but that cylinder that's misfireing has spark and fuel but I think too much fuel bc I took out all the spark plugs and they were all black so I cleaned them and put them back in but the car kept misfireing and losing power with the new engine I don't understand why it keeps losing power after swapping the engine please help!

My car has 140000 miles.
My car has a manual transmission.

Hello and thanks for writing in. There are a number of things that can cause the motor to over fuel or run rich. When this happens, it is usually related to things like faulty fuel injectors, a failing mass air flow sensor or a faulty fuel pressure regulator allowing too much fuel to be supplied to the combustion chamber to be burnt. I would recommend having an expert from Your Mechanic come to your home to diagnose your fuel system.

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Hi there - first task is to check for problem codes, even though this is an OBD I vehicle. Assuming your engine electronics are still relatively stock, there should be some information available on problems. You mention that all the plugs were black with soot - this suggests that fuel injection is too rich for all cylinders, because of something like a faulty coolant or air temperature sensor that is reporting a "cold" condition to engine management. A faulty ignition can appear as a misfire as well obviously, and also results in unburned fuel on the plugs. I recommend a loss of power inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, and give you an accurate assessment of damage and cost estimate for repairs.

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