Yes I looked at the chain when I had the valve cover off. it looks good

yes I have scanned the code every time the CEL has come on it is ALWAYS P0304.

currently, since we have had the AC on nonstop and the CEL has gone off, my code scanner shows the historic P0304. nothing pending.

to PulpFriction- I already used my borescope, leak down tester, compression test. you name it. everything points to #4 exhaust.

 

Order up head bolts and gaskets, a set of valves and pull the head

 

Will the new valve(s) need grinding or lapping?

 

historic code doesn't mean anything and does not light the CEL. Only a current code will light the CEL.
Historic means that it caused a CEL sometime in the last 99 cold starts. Pending means it has failed the test but, not as many times as it takes to become Current.
P0300 means "misfire detected, have not identified which cylinder, and might cause the cat to overheat or otherwise cause unacceptable emissions", it does not mean whatever nonsense your scanner "says", usually something like "random misfires" or "misfires on all cylinders".
There are 2 types of codes, P304 is type B. MIL = CEL.



You might check the connector and wires to the crankshaft sensor. If the crankshaft sensor or the ECM has ever been replaced the crankshaft sensor variation MUST be relearned, that is how a misfire is detected.

Vibration in the engine can cause the code, probably why the AC is preventing it. Look at the motor and trans mounts. If you look through the oblong hole in the passenger side wheel house and don't see a bolt head centered the motor mount is bad. Has the harmonic balancer ever been off, maybe not torqued causing vibration. Has the balance chain ever been mucked with, the alignment is important.

 

I still lap in new valves, but it’s sometimes not required

 

I am definitely not pulling the head. I just don't have the energy to put that kind of time and money into this car. car was bought cheap to be a beater. I'll sell it cheap to someone who wants to do the work. it drives perfectly fine. just the CEL would prevent it from passing emissions testing in PA

don brew- interesting on the motor mounts. I'll have to check. I have no history on the car prior to about a year ago (which was what PO told me crap mechanic did).

 

Fixing a bad motor mount will protect the flex pipe as well. Easy job if you have a floor jack. Still easy if you have enough mechanical aptitude to adequately support the motor with a selection of 2x lumber scraps. Tire changing jack from the cargo bay optional.

 

so i looked thru the wheel well, and the slotted hole has the bolt toward the very front, not centered. so i decided to replace that mount.

mount just came yesterday so hopefully change it this weekend.

interestingly, while checking things out i decided to clear the historic code, which reset all the emission monitors. have driven car exclusively with AC on for last 2 weeks. zero codes, all monitors have run and are good to go. so the car would pass PA emissions if i left the AC on. lol

 

Historic codes don't affect inspection, they are just evidence and clear themselves after about 100 clean ignition cycles.
I think your problem is probably related to the harmonic balancer or flywheel/flex plate. Maybe the balance chain.
Have you looked at the serpentine belt and tensioner?

 

Am I missing something? The leak down test showed leakage out the exhaust valves,why are we discussing all this other stuff (motor mount, flex plate,harmonic balancer, etc)?