# Carbon Buildup



## dono200sx (May 2, 2002)

When I originally bought the car, one of the first things I did was replace the spark plugs. When I got them out they were _covered_ in carbon. What causes this? Are there any specific parts for Z31s that are commonly problamatic that cause this?

I read in a past thread that automatic transmission fluid can be used in small doses to clean it up. How much is a small dose? Where is it applied? At the throttle body with the intake arm removed?

I'm at the point now that I am trying to chase down problems like this. I've got a couple other issues to look into, but I'll create specific threads for those so it's easier for people to search for.


----------



## dales86t (Nov 1, 2005)

carbons usually a sign of running rich. change your o2 sensor. If it were turbo, carbon would be normal. post a pic of your plugs and i'll be able to tell for sure. if its one plug doing it, then its a fuel injector problem, the injectors staying open at the pintle and isnt closing, clogged injector or dying electrically injector.


----------



## RocketRodent (Jun 21, 2004)

dales86t said:


> carbons usually a sign of running rich. change your o2 sensor. If it were turbo, carbon would be normal. post a pic of your plugs and i'll be able to tell for sure. if its one plug doing it, then its a fuel injector problem, the injectors staying open at the pintle and isnt closing, clogged injector or dying electrically injector.



Also the VG30 is notorious for carbon build up in the intake and the cylinder heads. Not sure if its a design flaw or what. Typically all that I've done is run a can of intake cleaner through. Now if you're ending up with a lot of carbon on the plugs, they could be old. 

But Dale86t is most likely right that you're running way too rich.


----------



## dono200sx (May 2, 2002)

The 02 sensor has already been replaced. I agree it is probably running rich. The plugs are completely black and smell like gas. One of them even had gas on it still, which leads me to think that the injectors are bad. 

I should probably take my VIN # to the dealer and see if they have already done the injector service on her.

Any ideas on correcting the air/fuel mixture?


----------



## dales86t (Nov 1, 2005)

Chuck in a bottle of injector cleaner (good stuff not cheap stuff), run a tank through and see what happens then. if not do a ECU test and see what it wants to tell you. Run fuel pressure test, and test AFM with multimeter as per FSM or service manual.my car runs rich too, i learn to deal with it, as the richness saves me having to tune it for higher boost on the track, anyways thats my thoughts, but it would also effect your mileage too, and pretty noticeable! Also check for vaccum leaks, as it will not compensate for the air.


----------

