1999 Pontiac Grand Am

The “Check Engine” light has been since we have owned this car. About six months. The dealers computer indicated a mis-fire on cylinder No. 1. To correct this problem we decided to change the plugs which did not seem to help. Next we changed the housing and the coil packs. The car still runs rough and we are not sure what to change next to correct the problem. Any ideas?

What kind of motor in this '99 Grand Am?

There was opportunity for parts swapping, rather than replacing. For example: swap #1 cylinder parts with #3 cylinder parts. If the problem moves to #3 cylinder, that part was causing the problem. Change #1 spark plug wire with another. Go to an auto parts store, get the free scan of the engine computer. If the misfire code is for the different cylinder, that spark plug wire is bad. Have the code erased with the scan tool. Swap the #1 fuel injector with another. Have the free scan done, again. Erase the code. If there is another part to swap out, I can’t think of it, right know. You?

2.4L Twin Cam 16V 4-cyl Enigine. That information comes directly off the new car sticker

This particular car does not have spark plug wires. We really hoped to fix the problem by installing new parts one at a time but that has not worked, yet! We had a scan done by an auto parts store and by a certifed mechanic. Both scans indicated the same problem. We pulled the new plugs and #1 was fouled real bad so I assume we have the problem isolated to that cylinder. I have not considered the fuel injectors. Are they easy enough to swap or cheap enough to just replace the injector for cylinder #1?

I suggest a compression check. See if that one cylinder is bad. At least you will not be throwing another part at it.

From the factory shop manual for my 02 Sonata:

PO301 missfire detected cylinder 1:

Possible causes:

  1. Vacuum leak.
    2.Ignition circuit malfunction
    3.Low compression. due to blown head gaket leaking valve or rings.(As Joseph mentioned check number 1 compression)
    4.Fuel injector circuit malfunction.
    5.Faulty fuel injector.

Okay, the wife won out and the car is going into the dealer this morning. I will post the results this evening. Thanks for all the suggestions.

My wife and I dropped the car off at the dealer this morning and told them all the service information disclosed above. At 2:00pm they called me to say they had a scan code that indicated a mis-fire on cylinder #1. Then they asked what I had replaced already? “Guys, didn’t we talk about this already?” At 4:00pm they called back to tell me they swapped the plugs and where still getting the same scan code. Now they are going to keep the car over night and in the morning put a testor on it to check the fuel injectors. I told them to check that at 7:30 this morning. More on this solution tomorrow.

Okay, my wife and I just got the car back from the dealer. “87 Ranger” was correct the fuel injector was faulty. For the record here is how the dealer stated the problem and solution, Scan check code P0301 #1 Cylinder misfire stored. Pulled coil cover and checked spark. Ok. Pulled plug and checked compression 200lbs good. Switch plug stayed at the #1 cylinder, also checked #4 ok. Injector coild test all 12.0 - 12.2 ohms. Performed injector balance test, 50lbs fuel pressure, #1 injector is lean. Replaced the #1 injector, cleared code and road tested okay.