I took off my valve cover to install new gasket, after reinstaling everything as it should be i start her up and now im getting missfire after a scan i got P0303 code which is cylinder 3 missfire changed coils and it didnt help .

give me some ideas as what can it be this time

I LOVE JAGS . . . . NOT

 

Explain which one you think is #3 as often people swap the wrong coil....

 

Passenger side 3rd. From the front of the car.

 

You changed the coil, cleared the codes and have this after that?

If so, could be wiring or even the plug.

 

You list has 2 cars? Is this the S Type or the X Type?
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01 S type V8

 

I would pull all the coils and plugs and just take a look first. You might have oil in the plug wells in one or more cylinders. Might have some rough looking spark plugs.

Did you change the cam cover gasket and the plug well seals on both sides?

Also the 2001 4.0 will have worn timing chain tensioners by now. This can cause random misfires too. Listen very carefully and you can catch the "death rattle" before anything lets go. The engine is an interference design so the pistons will hit the valves if you jump time or break a chain.

Do you get any rattling type noises on cold start up?
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I replaced timing chain tensioners about a month ago , everything worked fine until I changed rings and gasket on valve cover.

 

go over your work. def. missing sumtin

 

Check the plug wells for residiual oil. Even a little oil with crap out a new coil.

Also check the spark plug itself - possibly the insulator is cracked. Even a hairline crack will create havoc.

Finally, ensure the bolt that holds the coil is clean and has no rust on it - clean metal contact with the coil and ensure the coil harness is on snug - electrical contact grease on the coil connector and the bottom of the coil is always good insurance. Good Luck.

 

I have new spark plugs and new coils. I swiched new coil with old and still same problem.

 

If you swapped out all the coils and plugs, then you need to move on to wiring. Grab a meter and start looking for shorts to ground.

 

Good advice, but something too simple missed during install?

 

So i rechecked everything today installed different spark plug and coil still same code . . . at least i have a spark . . .
i really need your guys help on this one
here is what touchscan says:
P0303
Type: PowerTrain
Status: Stored
ECU:10
Description: Cylinder 3 Misfire Detected
as soon as this fixed she will get new tires and she is going up for sale . . . sad but i had enough fun with her.

 

You can read better details in the codes PDF in the FAQs and JTIS.

You're seeing absolutely typical code which affects just about any modern engine and won't clear on those either if something's still wrong. Just work through the possibilitites till it's fixed. Same with any engine.