I was driving the other day and noticed the car started to vibrate, and not to my surprise the CEL flicked on. I went to & had it checked, p0303, Cylinder 3 misfire. So after research online, I first tried to check the cylinder by removing the plug from the coil, to see if there was a loss in RPMs.There was, which I learned was normal. I proceeded to check the other 5, and all of them were losing rpms as they should. I replaced the coil on cylinder 3, but it is still misfiring.

I guess my question is, if the cylinder was acting normal when I unplugged it, could the spark plug even be the problem? Or would a bad spark also cause it to NOT to lose any RPMs when I unplugged it. I am going to replace the spark today but just want to be prepared if it is another issue.

 

Did you replace the coil with aftermarket or oem?

 

Possibility.

Also, swap the coil with the next cylinder over, clear the code and see if the misfire moves to that cylinder. That will rule out or confirm that the coils are to blame.

 

Perfect advice.

 

Also if the code stays on same cylinder, the only advice you will get here is to take to a dealer....lol

 

If compression and wiring is good with no vac leaks, then it must be the ECU, since the coils are direct driven.

 

That's a pretty rude comment towards all of us here on the forum. I don't think I've ever seen anyone say that. I am pretty sure that all of us like to try and help as much as possible. How far someone decides to take it is their issue. There are plenty of ways around a misfire EVEN if it stays on the same cylinder... Just have to use your head.

Thanks for the unappreciated and inappropriate comment. Good luck in your endeavours.

 

If the code stays on the same cylinder, then it points to the injector possibly being the culprit.

 

That's the one I left out lol. Brain wasn't working.

 

I'd go ahead and replace the spark plug first.

 

my 2002 SE developed the same P0303 problem recently. I decided to change all 6 spark plugs over the weekend since they were never changed after I bought the car new. To my disappointment, the problem still remains. Still rough when idle and the code came back after reset, repeatedly. So before I go to buy both the ignition coil and the injector for #3 cylinder, I like to know which is more likely bad, the coil or the injector. I regret that I didn't switch the coil btw #3 and #4, which would have told me if the coil is the problem and make an easy replacement. Would a dose of Seafoam in gas clean up the injector problem if it is the injector? I just hate to remove the intake pipes again. It gives me back pain. I don't see other related code, only the P0303.

 

Test the coil with a voltmeter, that will tell you if it is out of spec. On 20k setting the reading on 2 of the pins should read 1.49 or higher. It's either the middle and right pin or middle and left on the coil and make sure that the plugs that are in there are NGK's as these cars are plug picky, Bosch is like a guaranteed misfire if there used. The seafoam will only work if the injector is gunked up from bad gas, but If you wish to use it anyway( I use it here and there) run your tank until the gas light is on, add whole can, add 3 gallons, then step on it! By bringing it to redline the injectors are flowing as much additive as possible. Same goes for the original poster except for the seafoam part.

 

Before I put everything back, I did test the transistor as if it's two PN junctions. Both junctions seem to follow the V-I curve of silicon junction with the "elbow" around 0.67 v. What I didn't test is the secondary coil, or actual spark. For now, I will try a can of Seafoam with the remaining gas (about 1/4 tank).
Another question: if the coil is bad, shouldn't the exhaust smell bad since there is unburned gas? Since I don't smell that, does it indicate the problem may be that gas is not always injected to the cylinder?

 

With non OEM coils, they will "work" but also will throw a code. The problem with non OEM coils is that they aren't spec'd as well as nissans parts. All my coils worked but 3 were Chinese knock offs. They threw codes but still fired. If you can see the injector you could place a long screw driver against in and put your ear to the handle. You can listen for the injector ticking, if it is then your all good.