My 92 Lx has black soot build up on the rear near the exhaust.

What is the fix?

 

check your plugs. if they are bad this could be contributing or it could just be u have wrong plugs.

 

Your engine is running rich = too much fuel.

Is the CEL ON?

 

I dont know when plugs were last replaced so

I was going to replace the plugs with either NGK - Iridium Plug Item No: 2477 or maybe the NGK - Platinum Plug Item No: 7098.
No CEL on

 

Does your CEL work? It should come on for 2 seconds every time you turn the key to on (II) without starting the engine.

Since the car is modified you may have some mismatched parts.

Also the soot can be because of oil smoke from the engine being worn and burning oil.

 

Does the CEL work -- i.e., turns ON and then OFF in two seconds after turning key to ON(II)?

Is the engine misfiring at all? If not, check for an exhaust leak in the exhaust manifold around the O2 sensor. You also could have a lazy, malfunctioning O2 sensor or a bad fuel pressure regulator or fuel injector.

Is the engine idling to spec (~700 rpm) when warm?

 

CEL works
The exhaust from the header to the tail pipe looks all new. O2 looks new. Radiator looks new
I just looked at paperwork in glove box.
Timing belt and water pump replaced 8000 miles ago in 2008

 

You can't tell whether an O2 sensor, or a fuel pressure regulator or fuel injector, is good by looking at it. For specific details, download the 92-95 Civic service manual at the link in my signature.

 

Also can I take this to auto zone or somthing for a computer check?

 

don't use platinum or iridium
just use plain NGK V-Power