I have a 98 3.8 and have been having a problem with the engin missing. It runs great 99 % of the time. What happens is when you are speeding up slowley the engin will miss once in a while. I took the car on a trip where it was very hilly and every time I would go up hill it would miss the bigger the hill the worse it got. I have had the check engin light come on a few times and all it said is #4 cyl. had missed. I did change the fuel filter but have not done anything else. Any help on where to start or what to look for sure would be nice. Thanks

Check spark plugs, wires and coils, paying particular attention to cylinder #4.

https://www.gmforum.com/t278818/

If you suspect a coil, switch the coils around and see if the problem moves with the coil for cyliner #4 (do you have a scanner?).

In the dark, with the engine runnin, in park. high revs ... mist the engine compartment with a spray bottle of water and look for blue sparks (electrical arcing). This may tell you if a plug or wire is arcing to ground.

If you haven't changed plugs and wires, I would start there.

If plugs, wires and coils are all okay, switch the fuel injector from cylinder #4 with another cylinder and see if the misfire moves with the injector.

My guess is the plug wire or spark plug on cylinder #4.

Let us know how you make out.

Sounds like a weak spark. how old are the plugs and wires?

Thanks for the info. I changed the wires and plugs and so far it is running smooth. If it acts up again I will just chabnge the coil. Thanks again for the help

I would recommend testing the coil before replacing.