Lights flickering

[stamp11127]

You can also do the same test on the positive side of the circuit. I would make up a jumper with alligator clips on both ends so that it will be easier to avoid shorting out to ground.

Your positive cables may be an issue. Exposed wires will corrode and increase resistance in the circuit. That will lower the voltage and current flow. Since you are in the "Windy City" I know the amount of salt they throw down on the roads during the winter. I spent 6 six years at RIT back in the 80's. "Buffalo blows, Syracuse sucks and Rochester gets all the wind...."

 

[rtbrjason]

I did run a jumper cable from the battery to various places on the engine with no change in the flickering.

My friend/mechanic is suggesting we try a capacitor inline with the charging system. He has one laying around so it's free to try. I'm all for getting the flickering to stop but I feel like if this does work, it would be covering for a problem we can't seem to find.

 

[stamp11127]

When you have a chance please take resistance readings on the sections of the sense circuit for the voltage regulator. I've attached a pdf of the charging system for the 99's.

The circuit in question is #35 orange/light blue wire that runs from the C176 connector on the alternator to the battery junction box fuse #11. We will follow this all the way back to the battery in the following sections.

Then circuit 1119 red wire from the battery junction box fuse #11 to the ring terminal on the starter relay.

Then circuit 1118 red wire from the positive battery terminal to the ring terminal on the starter relay.

These tests need the battery disconnected so that the meter is what is supplying power for the test.

 

[rtbrjason]

Each of those 3 connections have 0 resistance.

 

[stamp11127]

I love this kind of problem, makes you think outside of the box. So we need to start the process of elimination.

What battery type are you using? AGM, Maintenance Free or conventional wet cell?

Is the serp belt tensioner staying still when running or is it bouncing up and down?

When you replaced the alternator did you check the other pulleys for smooth rotation?

Know anybody with an oscilloscope?

Another option would be to isolate the alternator electrically from the vehicle. You would use a second battery to supply current to it while using the original vehicle battery to start the engine, spin the alt and run the remaining electronics. The alternator would charge the second battery and power a few light circuits. That would let you know if the problem is in the vehicles harness. Let me know if you would like to try this.

 

[rtbrjason]

1. I believe it is a maintenance free battery. (AutoCraft Gold Battery, Group Size 65, 850 CCA 65-2: Advance Auto Parts)

2. The tensioner bounces at idle. Probably about 1/8" of travel. Tensioner/idler (both dayco parts) were replaced 3 years/15k miles ago in an effort to get rid of belt squeal. A gatorback belt was installed at the same time.

3. Everything on the rotating assembly other than crank has been replaced at least once. The clutch fan was removed for e-fans.

4. We looked at it with a scope a couple years ago. What do we gain from seeing the noise on a scope? I can probably get my friend to hook it up again and maybe get a short video if it will really help.

5. Is the 2nd battery a temporary troubleshooting idea or are you suggesting running the 2 batteries going forward to keep the circuit isolated?

We did try the capacitor as well but had no success.

 

[docraymund]

You might have a short circuit somewhere along the ignition line from the coil connectors to the pcm. It might be shorting to the alternator feed wire causing a voltage surge. This could explain the scope pattern and the increased flickering as engine speed increases.

 

[stamp11127]

Doubt the 1/8" bounce at the tensioner is the problem.
Your battery is a maintenance free lead acid type - nothing special for charging requirements.

The type of wave pattern on the scope gives you clues to what is happening internally and externally with the alt. Certain wave forms indicate different problems. It will allow you to see the sense signal from the battery and the corresponding voltage output from the alternator over time. It would answer the question of is the field coil pulsating? If it is, then that will produce the voltage variations you see in the lights. If it is pulsating then why is it pulsating? It is supposed to see just the current battery voltage on the sense wire and adjust field coil current accordingly. If the pulsation isn't from the field coil then what is causing the pulsation?

If you can get the scope on it we need to know the voltage highs and lows plus frequency in relation to rpm at the output stud. Same on the sense wire. A two channel scope is sweet here. Is the pulse tied to crank or alt revolutions?

Second battery would only be temporary. In essence you would be creating your own test bench using the vehicle/second battery combo. Need to be careful since you will be fooling the voltage regulator with certain wiring combos - output connected to one battery while the other is providing the sense voltage.

I've searched the net on this issue for additional causes. Sources have included issues with the pcm controlled alts (yours isn't), bad voltage regulators and just the wrong regulator in the alternator.

 

[rtbrjason]

Might be a little early to tell, but I think I might have this resolved.

Separating the alternator wires seems to have done it. They were running together in the same loom (the 2 wire connector as well as the larger wire). I had bought an alternator filter to try, and before it arrived I separated out the wires to get it ready for install. I started it up and didn't really notice any flickering.

After some time, I did see some really faint flickering (mostly in LED replacement lights) but I really have to focus to notice it. My headlights don't appear to be flickering at all, nor any of the green on the overhead display or climate control.

Previously, just firing up the truck with the headlights on parked in the driveway, caused the whole garage to flicker.. I'll be giving it a few days and lots of miles before returning the alternator filter and calling it fixed but looking good.

 

[docraymund]

Most likely a short somewhere in the harness that you touched. Check the harness in its entire length exposing all the wires and see if there are melted insulation. Something caused it and it should be identified and fixed.