Headlights causing a stumble.

[jimberg]

I discovered the weirdest thing yesterday. On my way to work, my engine was running perfectly. On the way home, it kept bucking and missing while at highway speeds. It actually did this on a previous night, and ran fine the morning after. Since it ran the morning after, I just figured that my computer was relearning the air/fuel ratio from when I changed the plugs the previous day and had finally adapted. The pattern is this: Runs crappy after changing spark plugs on the night I changed them. Runs fine the next day. Then runs fine the morning after that. Then runs crappy that night. The only thing different is that the headlights were on. Since there was still a little light left, I turned my headlights off to see what happen. Sure enough, the problem stopped. When I turned them back on, it came back.

Another thing I noticed with the headlights is that the water temp gauge reads higher by about 20 degrees. A while ago I used to think I was actually running hot, but now I know that something must be going on with the reference voltage used for the sensors or something. My only guess is that since I was running underdrive pulleys for a long time so they were not allowing the battery to fully charge. I installed a new, stock alternator and removed the underdrive pulleys.

Could the battery still be weak because of all the abuse it took from not getting fully charged, or do you guys think it could be something else? The car starts fine and all, but whenever I run the fan or turn on headlights, I can see the voltage gauge drop a couple volts. I've checked the grounds and they seem okay. The battery goes to the block and then the block has a strap to the chassis.

I may try to have the battery replaced, but since it really isn't dead, I'm not sure if they will do it under warranty.