Been running great since intake gasket replacement 5000 miles ago. Also recently replaced MAF and MAP sensors.

Things I've done since misfire popped up yesterday:
New plugs today, I did champion copper core.
Checked for vacuum leaks with smoke test, all is 100 percent sealed.
Checked for dirty throttle body, all looks good.

Possibly egr stuck open? I did notice decent amount of smoke when first started, could be residual from smoke test escaping into the exhaust through egr valve?

What about his ignition capacitor, I'm thinking that would only be on startup.

 

Putting my money on dead/dying coils

 

I was thinking that but why would 2 go bad exactly same time?

 

Could be a cascade effect. Mine threw multiple cylinders when only 1 was bad.

Also, glad I'm not the only one with an LR3 and a trans am (have a 99 Firehawk)

 

I assume you replaced with copper core that are east least iridium or platinum plated? They will not last long if not. 15k miles at most.

I am not sure on the Jag 4.4, but most COP setups used a wasted spark setup. So two coils fire at once and are wired in series. Depending on the type of fault with a coil it can affect its companion.

edit: Looking at your pics of the original plugs, they seem rather oily and should not be that bad. If your COP tower seals are bad and oil is collecting on the coil boots you will get misfires too.

 

Thanks
I always use copper. Yes I know they don't last as long.

Just the combustion part of plug has a little oily carbon build up.

 

swap coils to opposite bank. Also you running premium fuel? I would also spray intake area with brake clean to verifiy that intake not leaking since you mentioned it.

 

Well the misfires age already in opposite banks. Also I smoke tested intake and no leaks anywhere.

 

The 4.4 is hyper sensitive to vacuum leaks. I never trust smoke tests, they are only good for large leaks as far as I am concerned. Also if the PCV valve fails it will not show on a smoke test. Things that can easily cause a vacuum leak are the PCV (as mentioned), oil filler cap or neck, oil dip stick and if the throttle body has been removed and the gasket re-used. The PCV is easy to test by simply removing it and blocking the hole in the valve cover and hose. But I would expect more misfires than just two. Moving the suspect coils around would certainly help determine if they are the issue or not.

 

THank you sir! I have been through all of the vacuum issues in the past when i found the big leaks at the manifold.

New coils should arrive tonight! I will keep you all posted.