I've got a 93 Civic CX.

I recently dropped in a JDM ZC motor (D16A6).

The car runs great and my fuel economy still seems normal but over the last 3 or 4 days I've noticed a small puff of black smoke at high rpms or under strain and my tailpipe is collecting a pretty fair amount of soot.

In the last 5000 miles its had fresh NGK plugs and NGK wires, new cap and rotor, and a new fuel filter.

I haven't pulled the plugs to check them yet but as of 2 weeks ago they looked like they were burning perfectly.

The car is running on the factory P05 ECU and has the one-wire o2 sensor.

I'm not getting a CEL and the ECU isn't storing any codes.

I haven't taken it for emissions yet this year so I'm not sure what my levels are.

What are some things that could be causing this?

 

Anyone?

 

injectors might be dumping? try swapping them out with your d series ones see if it changes anything..

 

I'm not familiar with the CX as I have an 96 EX. I'm having a rich mixture issue as well. Thought I'd share some of what I've found in case it helps you. My first thought is that if you are running rich and the CX has 2 O2 sensors like the EX, you should be getting at lest one 02 code: P0138 = high voltage 02 Sensor #2. The soot you describe does sound like rich exhaust (black). My suggestion would be to run down your fuel system:

1. Check injectors with a "noid" light & or resistance to see if they're working right.
2. Take a look at ignition timing to be sure it isn't off allowing unburnt fuel to be lost on the exhaust stroke .

Just a few thoughts. Good luck