Q: replaced bad coil pack and new coil not sparking car starts but runs rough engine light on blinks sometimes

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Car started running rough while driving. tests revealed bad coil pack cyl 1&4. replaced coil still not firing now #6 not firing too. Car starts right up runs rough and even more rough when shift into drive or reverse engine light on and blinks when accellerator is pressed. Car has over 250000 miles but was rebuilt about 10 months ago. Car was operating fine and noticed gas milage began to decrease in last couple weeks this problem started 3days ago. Spark plugs and wires replaced about month ago. Would appreciate some direction to take troubleshooting or a diagnosis. Thank You.

My car has 250000 miles.
My car has an automatic transmission.

Hello and thank you for your questions. If your engine was rebuilt about 10 months ago, the question is to determine if the management system has been installed as well. With the symptoms that you are having, it sounds like the coil packs are old and in need of replace. You replaced numbers 1 and 4 and now number 6 is not firing. I recommend replacing number 6, 2, 3, and 5. This will ensure that you have all 6 coil packs that are new.

Just because the coil packs are okay during a test doesn’t mean that they are functioning correctly. Coil packs on Buick vehicles from 1998 - 2005 last between 150,000 to 200,000 miles. I also recommend having your fuel injection system flushed. Unless you have new injectors, the old injectors could cause a cylinder to fail, even though it is working correctly. These symptoms can cause the engine to have a rough idle and rough running during conditions. If you need assistance troubleshooting the rough running condition, I recommend having a professional, like one from YourMechanic, inspect the car and move forward with repairs.

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