We removed the stock exhaust manifold from his B18C1 to install a JDM 4-1 and discovered that 1 chamber was full of real dark carbon deposits and the other 3 to be pretty clean. What I saw was that the difference between the dark chamber relative to the other 3 was like night and day. One was covered in black while the others are a light gray as if they had been cleaned a day before.
We put the stock exhaust manifold back on and spent the rest of the day trying to figure out what the problem is. When he first got this engine/swap about 2 months ago, it only had 30,xxx miles on it and he has added about 7,000 miles (for a grand total around 37,xxx).

He said that his car has been feeling real slow as if it doesn't pull as hard as it used to (hence the header install in an attempt to gain a couple of horses and some torque).

He also told me that his Check Engine Light (CEL) comes on and off throughout the day while driving around town.

When we took the stock manifold off my other friend's B18C1 (which pulled strongly, real hard, and "normal") to replace it with a DC 4-1, all chambers were completely covered in dark/black carbon deposits and they didn't vary too much from eachother and this engine had about 4x,xxx miles on it.

What do you guys think the problem is? Faulty injectors? Faulty spark plugs? Bad air:fuel ratio? Faulty Computer?

Please help us out as any information would be greatly appreciated.

TIA

 

There are a couple of things that I would do... First, find out what codes the computer stored when the light comes on. If you have a book, it will tell you how to do that. Second, do a compression test. That will tell you a lot about the condition of the engine and valve-train. Both of these are very (fairly) easy to do and could be done in a couple of hours and save a lot of guess work time.

 

davija: Thanks a lot. I really appreciate it.

Anyone else?

 

compression test
should be the #1 thing even before posting on HT when a problem occurs on the internal side/combustion side of the engine.