Pontiac Repair: Problems with Grand Am, light flickers, check engine soon light

Question
I have asked this question to the other Pontiac expert too - trying to get as much advice as possible - anyway, I have a 1999 Pontiac Grand Am SE - a 4 cylinder - don't know anything about the engine size. Background - A few months ago I was about an hour away from home when I purchased gas and about 1/2 way home the car started hesitating and I thought that I had bought some bad gas. My "check engine soon" light also came on and the "trac off" light came on at the same time. I took it to AutoZone as soon as I got home and they hooked it up to a machine. The machine said "Cylinder #4 was misfiring" so the guy asked me how long I had the car, how many miles it had on it and had I ever changed the plugs and wires. I told him I have owned the car for a couple of years, It has 130,000 miles on it and no, I had never changed the plugs. I found a guy to change the plugs and wires for me, but he said I didn't have wires I had 'boots' and since he couldn't remember how they were put on he knew he put them on different. (During this time, I also noticed that I got terrible gas mileage)So, we decided not to replace the boots. After he replaced the plugs, I drove home and it was doing better then a couple of blocks from home it started hesitating again and the "check engine soon" light came on again. I took it back and he thought maybe it needed a new coil pack - so, I bought one and he installed that and it wasn't any better. I took the car back to AutoZone and they hooked it up on the machine again and it read the same thing "#4 cylinder was misfiring". Anyway, whenever I go down the highway my "check engine soon" light flickers on and off and my "trac off" light comes on. I don't know what these two things could have in common but I am sure they are related somehow. Also, a couple of weeks ago, I was stopped at a light and turned my a/c on and my car died. It started right back up but I figured I had an unrelated a/c problem. But yesterday, I had to turn on the defroster and I was again parked. When I turned the fan on, the car started to die - it didn't though because I pushed on the gas pedal and it straightened right up. I was just wondering if these two problems were related? And, I don't have the money to replace things that aren't wrong with the car. Thanks for any help you can give me. Darra Taylor

Answer
Hi
First let me explain the TRAC OFF light.
It WILL come on when the service engine soon (SES) light is on, due to the fact that when the wheels start to slip, the Anti lock braking system "pulses" the slipping wheels brake system trying to keep it from slipping. If it sees no difference in slippage, it "requests" the cars computer (PCM = Powertarin Control Module) to limit torque, so the wheel will stop slipping. (all this takes place in  milliseconds) All that being said when there IS a problem with the PCM's controlled systems eg.. a #4 cylinder misfire, The Traction Control system will be disabled until the fault no longer exsists. That is why the TRAC OFF light is on.
Now, I would have the following items checked for a misfire cause:
(first make sure a Delco plugs were installed. This is VERY important.)
1) The Coil Housing. This is the large housing the 2 coils are mounted into and the plug boots hook to.
It is made of hard plastic. They are VERY common problems creating items.
2) The #4 Fuel injector. If the "stream" of fuel is not correct, it is drips or dribbles. If the nozzle is partially blocked, due to contaminates in the fuel.
Have the Fuel pressure checked. Also have the Fuel pressure regulator checked. By taking off the Vacuum line of the Pressure regulator, if ANY fuel is present, it needs replacment.
3) An engine mechanical problem can cause a misfire. Reading your story, I really doubt this is your problem, but it IS a possibility, if all else fails.


maintance items to consider...
1) Get a Fuel Injector Cleaning service preformed by an auto shop your familiar with that preforms this service. If you dont know any, ask relatives, friends or coworkers...
The shop (if they know what they doing)could preform a Fuel pressure drop test. This test primes the fuel system, and then pulses the selected injector. If the fuel pressure drops evenly across all 4 injectors, the flow is correct. Have the fuel rail cleaned also.
If not corrected by Injector cleaning...
You could also  have the mechanic swap the injectors from #4 to like #2. see if the misfire follows the injector. If so, your injector is either faulty or clogged beyond cleaning. (they could also do the same with the spark plugs to see if they still good.)
Lastly would be to preform a Compression check to check for engine mechanical failures.
As far as the stalling, the A/C compressor comes on in Defrost made to dehumidify the air hitting the windshield (even when placed on full hot the compressor runs).
This extra Load on the engine, I'm sure is causing your stall/near stall.
I hope all this helps in some way.
Just advice from experience.
Good Luck
Pawl