The wire set I put on the car are from magnacore and the spark plugs are 3E plugs, that was done several months ago, the code reader that i got the codes from used to be able to erase the code so you could tell if the codes would come back but they no longer have that function because they had to make a new policy because people would use the code reader, get codes, swap out the bad parts and try to get their money back saying the part was good

just how many computers are there on a 1999 buick, some diagrams have one under the hood by the fender on the driver side and another under the dash by the glove box?????

My 1999 buick lesabre check engine light came on, I went to my local O'reilly'* auto store to use their code reader, and got a code P0304-#4 cylinder misfire, I had several months ago put new plugs and wire set on the vehicle, magnascore wires and 3E spark plugs, I could not erase the codes to see if it would come back because they had to make a new policy at O'reilly;* saying they are not allowed to do that particular function with the reader. the funny part is that i just had 4 new tires put on the car and within a few days the check engine light comes on, smells kind of fishy because i had no check engine light before that

A tire shop putting new tires on a car has no business even opening the hood. There is nothing they could have done in the course of changing tires that could have brought this issue about.

And there are quite a few computers on the car, including ABS, Airbags, etc. Also multiple modules are present that could possibly act like computers as well.

I have done some interwebbing, and it seems that E3 spark plugs have a fairly inconsistent reputation in 3800'*. The favorites are usually NGK Copper plugs, or iridium. These engines use a waste spark ignition system, where 2 spark plugs are getting fired at the same time, and spark plugs are fired twice as often as traditional systems. It has been known to be pretty merciless on spark plugs and wires, especially platinum plugs.

I also don't know anything about the brand of wires used.

The codes should clear themselves if the problem does not reappear within a specific timeframe. If the problem persists, I would pull the spark plugs to have a look at them.

the shop where i took my car to also does mechanical repair as well, I have heard lots of stories about how a mechanic shop would fix a problem with a car but would also mess with something else trying to get into your wallet again, just saying

went to genuine parts and got an HEI spark plug tester, hooked it up, started the car and got good spark action

that means the coil to #4 is good and the ICM is working, therefore it must be something else

the wire set is made by magnacore in detroit, did a lot of reseach and these are a top choice

that is an incorrect spelling it should be MAGNECORE

I have read that the ECM could also cause misfires and other problems, making the car shudder and the like, but also a bad head gasket, low compression etc