Please help me with a car problem

• Doing 60mph on an incline, I pressed down on the accelerator and nothing happened. What's going on? I replaced the alternator on my 2000 Chevy Astro minivan yesterday. Today, I had an acceleration problem. Are these two incidents related? Yesterday morning, I started the car and my battery light was lit. Battery guage began dropping as I drove it to a repair shop. Pulled into a garage to have it checked and it died within moments while idling. They replaced the alternator with its belt, and recharged my battery. After the alternator was replaced, I drove it on a highway at 50mph for about 10 minutes last night and for about 15 minutes on local streets in Queens, NY. This morning, my family and I got in the van to drive to CT. I was on a steep on-ramp for a bridge about 5-7 minutes later, when I put my foot on the gas to make sure I didn't lose too much speed. The engine raced but the van didn't accelerate. I pumped the gas. Each time, the engine would race as if I were in neutral. My "service engine soon" light began flashing. I put on my hazards and the car's speed dropped to about 40mph, at which point the gas pedal began working again. The "service engine soon" light stopped flashing and stayed solidly on. Hours later, it's still on. I stopped at a gas station on the far side of the bridge. Filled my tank. Checked my transmission fluid. Clear, and a good level. Oil is fine. I drove cautiously to CT and didn't go over 55 at any point in the trip. Just drove home. The problem didn't re-occur. Some questions: What the hell happened? What should I do now? How do I make sure this doesn't happen again? Should I try and see if I can recreate the problem? Is the minivan still safe to drive? Is it possible that this is in any way related to the alternator being replaced yesterday? If so, did I not run it for long enough on the highway last night to make sure the battery was properly charged? My manual says that the "service engine soon" light goes on when emissions rise above acceptable levels. How is this related to what happened? Any advice as to what my next steps should be? I'm planning to take the car to a mechanic next weekend, but I'd like to know what to expect now.

• Answer:

  My "service engine soon" light began flashing. A vehicle's Service Engine or Check Engine light will flash ONLY if the car is experiencing a misfire. There is no other condition that will cause the Check Engine light to flash. That's true for every single OBD-II vehicle in production. Flashing as the result of a misfire is a mandated function that's part of OBD-II. When the engine misfires, a condition is occurring in one or more cylinders that results in the fuel not being burned. The engine computer detects this through fluctuations in the RPM combined with oxygen sensor readings. When the engine stumbles, the RPM signal fluctuates and unburned fuel in the exhaust will change the oxygen sensor voltage. Unburned fuel in the exhaust constitutes an emissions increase (hydrocarbons -fuel- being excessive emissions). The light will flash when this occurs because the catalytic converter (the exhaust component that chemically cleans the tailpipe emissions) can become extremely damaged as the result of prolonged misfiring. The converter operates best when hot and when unburned fuel enters the exhaust, the hot converter can reignite the fuel and subsequently begin to melt itself. Although this damage typically requires prolonged neglect of the malfunction, I have seen bad misfires cause converters to glow cherry-red-hot after about an hour of idling. It depends on the severity of the misfire. A number of things can cause a misfire. The engine needs correctly proportioned fuel and air combined with correctly timed spark to make the requisite combustion to motivate the car. Your Astro Van has a Mass Airflow Sensor located between the air filter and the throttle that helps the computer determine the amount of air flowing into the engine. Since I'm sure they removed the air filter housing and ductwork to get to the alternator, check to see if it's hooked up correctly. If the engine computer can't calculate airflow, it will run very poorly. Double check that other sensors, like the throttle position sensor are connected and weren't disturbed by the previous work. Also, check and make sure that all of the spark plug wires are connected tightly. Aside from double checking the work, you're really going to need to get a scan tool hooked up to the van to determine the source of the misfiring and to clear the Check Engine light. If the repair shop is a reasonable distance from your home, I recommend taking it back there and making it their problem.