99 Olds Cutlas misfire

My wife and I bought a 99 Olds Cutlass new. From 50,000 to now, near 72,000… the engine runs rough once in a while and the error code displays an engine misfire. I replaced an ignition coil and that seemed to do the trick for a while. Now winter is here and it’s acting up again. Plugs/wires were done this fall as well as a second ignition coil (different cylinders, is has 3 coil packs). I am at my wits end with this car. My next step was to take it in and have the injectors chemically cleaned. I am concerned I am going to end up with a large bill if they start replacing injectors. Secondly, I am not sure how they will tell which one is acting up if the symptoms don?t occur while it?s in the shop.

Are you getting a CEL (Check Engine Light)? If so have codes pulled again and it might tell you what cylinder is misfiring. Post what code number you are getting.

Just curious. What was the code that was set when you replaced the first coil?

If your engine is still misfiring I have checked to see which cylinder it is by pulling the plug wire off each cylinder one at a time while the engine is running. Listen for the one that makes very little change in the running of the engine. WARNING! Be carefull doing this! Make sure you are insulated from the voltage as you can get a large shock! Use rubber gloves or insulated boot pliers to pull the wires. This may also set a CEL. If it does then you will need to have your CEL reset at one of your local parts stores that pulls and resets these codes for free.

Yes, I the check engine light is either on or flashing. The code is usually on cylinder 1. Actually, it was the first plug wire I replaced when troubleshooting. In the past, the mis has always gone away when the car was either warm or been restarted a time or two. Tonight, I drove it hard, up some hills, many restarts. The CEL still flashes, telling me quite obviously, the problem hasn’t gone away and it’s rough idle from a stop. I have an code reader. It’s almost always on 1 or 6. which ever has been on the same coil back. So it has new coils, new plugs, new wires. Is there anything else I can check without taking it to the dealer?

You can swap the ignition coils. If the misfire moves with the coil, then, you know it’s the ignition coil which is causing the misfire. The Haynes, or Chilton’s, repair manual will give you the voltages and resistances to check for from the igniter or computer. All the electrical readings can be good, and there can, still, be misfire, unfortunately. /// Use of an intake manifold spray cleaner could help.