I got a 2002 mercury cougar, check engine is flashing. i had it diagniosed by autozone. they say misfiring on number 3 cylinder. i replace plug,coil pack,and injector. And its still misfiring....Could it be a valve stuck?..

When your engine light flashes about 95 percent of the time (f not more) means that your vehicles computer (PCM) has detected a misfire and that the misfire at the time it is flashing that the misfire is bad enough to cause damage like to the catylist converter(s), oxygen sensor and a number of other things. You need to find out which cylinder has the misfire. You can go to your local auto parts store and most of them will pull diagnostic trouble codes (DTC\'s) for free. Now once you get the DTC(s) you can narrow down whcih cylinder(s) has the misfire by what DTC they pulled. For example a DTC of P0301 means a misfire in cylinder 1, P0302 would be cylinder #2 and so forth. A P0300 means multiple random misfire a much further testing needs to be done in order to diagnose. Say you have a P0301, depending on your engine size you will need to isolate cylinder # 1 to diagnose. If you have a 3.8 liter engine in most cases it\'s the fuel injector ot a bad spark plug wire for that cylinder that is bad but if you have the 4.6 liter most common cause is a bad ignition coil for that cylinder as they have a seperate coil for each cylinder but it could be an injector too instead of the coil. I\'m just giving you the most common causes but diagnosing needs to be done in order to replace the faulty part(s). Other causes of a misfire are crank or cam position sensors, a vacuum leak, Faulty spark plug wire (if you have the 3.8), engine problems (internal), electrical and/or wiring problem or even the PCM. Many other things can cause this, these are the most common. Gatting that DTC is vital in order to diagnose. If you need further help as far as testing procedures once you get any DTC\'s I\'ll be happy to helps you diagnose the problem. Hope I was able to help you understand what\'s going on...

you can have a stuck or bend valve in cylinder 3

misfire on cyl no 1 on a 01 merc grand marq

Do a compression test on all the cylinders, If all the cylinders are ok them I would be checking the #3 fuel injector

try some seafoam to unstick lifters

You don't mention the DTC, but I assume the fellow @ Auto Zone knew what he was talking about. If it is an intermittent misfire, I'd first look into plug wires. A broken wire can sometimes misfire....but it'll only get worse with the passage of time.

Might be a really good time to consider a tune up....plugs, wires, air filter, etc.

Its time to do a injector balance and cylinder leakage test, to determine whether the injector or its circuitry is bad . The leakage test will tell you if the cylinder has a compression leak.

first take it to have the codes extracted then post them and I may have an idea as to what may be wrong with it. I know autozone will extract the code for free some other shops may as well.

On the 2002 Mercury Cougar
For the 2.5L V6 DOHC:

Firing Order:
1-2-3-4-5-6

Cylinders:
.....(back)
1......2......3
4......5......6
.....(front)

Ignition Coil:
.(back)
4...6...5
3...2...1
.(front)

Had the same problem, car was misfiring on cylinder 3 and 4. replaced wires, plugs, and ignition coil. still misfired on the same cynlinders. turned out the main engine wiring harness plug in was coming loose. spent well over $150 on the unneccesary repairs and ultimately fixed the problem wit a $3 bag of wire ties to hold the plug in...