2000 LC Belt Tensioner Question - Pulsating Lights

[Ronel2020]

I recently noticed that my headlights and dash lights were pulsating in rhythm with the motor. Around the same time, the alternator/battery light came on. I assumed that that alternator was going bad (replaced the battery a couple of months ago) and replaced it. At that point, the alternator light went off, but I still have pulsating lights. The needle on the voltmeter is also moving up and down in rhythm with the motor. This evening, I check and cleaned the battery terminals and the grounds, but I still have the same problem. I started looking at the belt while the motor was running and noticed that the guide (pointer) on the tensioner was bouncing back and forth between a couple of the tick marks. This movement was in the same rhythm as the pulsing lights. Is it safe to assume that the tensioner has gone bad? I have no idea if it has ever been replaced. Thoughts?

 

[SmoothLC]

Try a stethoscope - mine was going out and it was fairly easy to determine using one.

 

[Sandroad]

The new tensioner is a reasonable next step, but I have a hard time believing that's slowiing the engine enough to cause headlight pulsing.

 

[PADDO]

I recently noticed that my headlights and dash lights were pulsating in rhythm with the motor. Around the same time, the alternator/battery light came on. I assumed that that alternator was going bad (replaced the battery a couple of months ago) and replaced it. At that point, the alternator light went off, but I still have pulsating lights. The needle on the voltmeter is also moving up and down in rhythm with the motor. This evening, I check and cleaned the battery terminals and the grounds, but I still have the same problem. I started looking at the belt while the motor was running and noticed that the guide (pointer) on the tensioner was bouncing back and forth between a couple of the tick marks. This movement was in the same rhythm as the pulsing lights. Is it safe to assume that the tensioner has gone bad? I have no idea if it has ever been replaced. Thoughts?

You don't say if this is occurring at idle only, hot or cold engine and is it across the rpm range. What's your idle speed when all this is happening and are you seeing approximately 14.2v - 14.6v at 2000 rpm? You may just be seeing low alternator output due to low, rough idle speed which should be around 800 rpm warm in neutral and around 650 warm in gear with no AC. If you do have low, surging idle give the MAF and throttle body a clean, disconnect battery for 10 mins to reset the fuel trims, maybe run a can of good fuel cleaner through (BG 44k is good) if that hasn't been done in a while.

 

[Ronel2020]

The LC idles fine. Steady idle warm or cold. Not certain about RPM at the moment, but it is likely within the range mentioned by PADDO. The pulsing lights occurs across the RPM band whether at idle or at highway speeds.

Is it normal for the tensioner to rock back and forth when the engine is running?

 

[PADDO]

The LC idles fine. Steady idle warm or cold. Not certain about RPM at the moment, but it is likely within the range mentioned by PADDO. The pulsing lights occurs across the RPM band whether at idle or at highway speeds.

Is it normal for the tensioner to rock back and forth when the engine is running?

My tensioner is dead steady at idle, no discernible movement. Original tensioner at 140k, belt is OEM with 50k on it.

 

[hoser]

Could also be one of your pulleys is on the verge of seizing. Slacken your tensioner and inspect your pulleys one by one.