My "check engine" light is blinking!?

The "check engine" light is part of your car's onboard diagnostics (OBD) system, when a mechanic connects he's diagnostic scanner to your car's computer it displays a code and in this case the code has revealed that it is a misfire in cylinder 3 ( as you have stated, i just wanted to explain that the check engine light comes on for many reasons not just that )..

Anyway, a misfire could be a few things firstly i would check the spark plug for that cylinder, if that didn't fix it i would replace the spark plug leads, and depending on what type of car it might be the distributor or rotor button....

If i knew what type of car it is i could tell you which one is cylinder 3 and if it has a electric disy cap or not, to help narrow down the problem, but i think you'll solve this issue with step 1 by checking the spark plug...

Well if u have the money,u need to take this in to a good service station.They will have a better computer,that checks deeper than auto zone.(auto zone will give u a list of what several of the problems could b)but if u change everything it says u could spend thousands.A service station with a good computer,will pinpoint the exact problem and should let u know how much it will b to fix it b4 they fix it.The place I go to charges $46.to plug it in,but they take that off if they do the work on it.Sounds like a small problem to me but u have to know the exact part to replace.

It blinks when it is misfiring.

You ever seen a 3-legged dog try to run?

That's what you're car is doing right now.

You are running on 75% power.

FLASHING CEL IS VERY BAD IT MEANS MISFIRE. DO NOT DRIVE IT CAN MELT THE CATS DOWN. VERY VERY EXPENSIVE. tO SAVE UR CAR GET TO A TECHNICIAN ASAP BEFORE YOU DO MORE DAMAGE.

Sounds like a broken sensor. You have to take it to a good mechanic/dealer to have it looked at.