rich or lean
 

how do i make sure my engine doesnt run rich or lean? and how can you tell if your engine is running rich or lean?

If its stock, with no mods to the air intake or fuel system, then it will be fine because the engine computer takes care of the mixture to make sure it doesn't lean out. If its got mods to the fuel system like bigger fuel injectors, you should get a device that piggy backs off the stock ECU to control fuel delivery and have the car put on a dyno so you can watch the fuel curve. It will graph it for you so you can see when its getting lean, and use the device to increase fuel to the mixture. You can also get a air/fuel mixture gauge, but there is some debate as to how accurate those off the shelf gauges are. Most people who are seriously into tuning cars will tell you you need a wide band O2 sensor. They usually run close to $1000. You can use a EGT gauge to monitor exhaust gas temps, since the temp curve is directly related to the air fuel mixture, but you have to know what you are doing. This A/F gauge seems to be a great value. http://www.innovatemotorsports.com/

If its heavily modified, you can get a complete engine management system where you program ever aspect of engine operation. Fuel delivery, spark timing, ect...

Hope that answers your questions.

i have a K&N air filter, and an aftermarket exhaust and downpipe. soon ill add a cold air intake and a front mounjted intercooler. With those mods, should i use a piggyback or a new engine management system?