CarNoobLovingIt

1st, I apologize if this is in the wrong section. I'm still new to this forum thing.
There's actually quite a few questions I have but I will wait until the thread gets going to ask them..
How can you tell if your car is running lean or rich? Is there a specific sound or smell that's a giveaway? I recently upgraded my throttle body and plenum 75 millimeters. one of the guys in my unit used to own a car shop and talking to him he told me to be careful and make sure my car is running lean. I told him I got a sct tuner to tune it but he said even with that be careful. so how would I be able to tell?

dawson1112

I am assuming he meant to say make sure it is not running lean, because a lean mix is bad.

Your computer monitors the air/fuel ratio, and will alert you via a DTC and check engine light.

How ever lean running engines tend to run hotter, back fire or pop , also some times get a pre ignition knock while under load.
Rich mixtures tend to smoke black out the exhaust , especially when you go wot. You may also notice a lot of unburnt fumes from the exhaust and sometimes may even burn your eyes.

If you don't have a check engine light and show no codes I wouldn't worry. If you still want to know pull a spark plug and examine it. They should be a light tan color, If they are very white chances are your running to lean, if they are very dark almost black chances are you are very rich.

The computer detects the mixture using the 02 sensors, and will adjust accordingly.

CarNoobLovingIt

So say for instance I went from my 75 mm TB and Plenum to say 80 or larger I would need to swap the injectors for larger ones to prevent a lean mix?

uberstang1

Pull the spark plugs and inspect.

dawson1112

No you only need larger injectors when you have a lot of supporting mods that would require more fuel. Your PCM is quite capable of keeping the air/fuel ratio where it needs to be, even with a larger TB.


You would only run out of fuel on the big end, when your rpms are high, and you have a lot of power adders. Your stock injectors should support you up to around 350-400 hp.

Now if you have a tuner, you have to be care full if you start messing with the fuel table, because you can pull too much fuel out. Most of the canned tunes done with out a dyno will er on the side of to rich.