I have an annoying flickering of all my lights (interior, digital dash and headlights) when the car is running regardless of electrical loading. It is definetly worse at idle. I checked all the grounds and inspected all the cables. I cleaned some of the contacts and this made it a little better. Alternator puts out 14.2 volts consistently so I think the regulator is good. It is the 97 amp model. My question is: has anyone had this problem and found it to be a bad rectifier diode? There are 3 diodes and a capacitor in the alternator and I was wondering if it would be wise to try and change them even if they checked ok with a meter or should I just put a better 108 amp alternator in it? It seems to me a diode may be bad causing the flicker as it is not smoothing out the ac voltage to dc. Sound right? Any suggestions? TIA Mike PS The battery seems fine. It always starts strong.

 

With the engine idling, unplug the connector on the alternator. If the flickering stops, you have a voltage regulator inside the alternator that is oscillating. An auto electrical shop can replace the regulator much cheaper than you buying another alternator, rebuilt or not. Defective rectifiers don't cause flickering.

 

I would think that the battery would work along with the alternator supplying 12 volts to all your lights. If the alternator could cause a flicker, then when you unplug the alternator the lights would drop dimm real fast. This just does not happen, the battery carries the entire load until it "eventually" sllllowlyyy dies. I would bet you a Coca-Cola that you got a loose ground. Look up the lighting diagram in your FSM and I am certain that it will be obvious where the loose ground is. Sorry I am at work and dont have my FSM with me.
When you say flicker, I assume that the lights are going "completely" off momentarily, correct?

 

Clean and tighten all your battery and alternator connections. If there is no improvement, remove your alternator and take to a local rebuilder for testing. If it's bad they can fix just what's wrong.

 

You will not pull full current from the alternator. Hence a open diode would not even be obvious by its operation. The alternator just would not have full current capability and would not cause a flicker as bad as you have. Besides the battery will absorb lots of voltage transients like a capacitor. (Aside from that, the frequency of the rectification would be to high for you to see). You have measured the alternator output at 14.2 volts which is fine which should rule out the regulator at this time.

Measure the headlight voltage, its easy to get there. Then you can see at the source of the problem and what the voltage is, it should be moving around quite a bit as you described. Then you can figure out if you have a poor connection somewhere and trace it backwards.

 

Thanks for the help guys. I have checked every ground I can find and all the connections. They are all tight and corrsion free. The battery cables don't have any rsistance in them when reading with an ohm meter. The lights never totally go out just flicker bright to slightly dimmer. Sometimes you can't even notice unless you know it is there and sometimes it is quite pronounced. Someone on another site mentioned this is a common problem with 84 alternators. In absence of finding anything else wrong, I'll probably get a newer style 108 or 120 amp alternator. I know more amps has nothing to do with the flickering but if I'm going to change it then I guess I'll upgrade. I just don't feel right having this power flux with the digital dash. I expect it needs clean voltage or failure is predicted. Can anyone recommend an upgraded alternator that will fit the stock mounting brackets?

 

Oh yeah, one more thing. There is no flicker with the engine off and just running things off the battery.

 

Re-read JFB's post. As usual, he's on the money.

Be well,

SJW

 

I'll give it a shot. I'm just hesitant to do that because I've been told by others that it caused their ignition module to burn up when doing that. I just think that if the regulator was oscillating then you would see it on the voltmeter varying slightly from the 14.2 to slightly less. I guess I can check for steady voltage at the alternator to ground with my multimeter also.

 

Your multimeter cannot respond to the frequency your alternator is oscillating at. You cannot hurt anything by unplugging the alternator with the engine running. If it bothers you, unplug the alternator and then start the engine, and plug it back in with the engine off. If you have an oscilloscope, or access to one, look at the waveform across the battery and you will then be convinced that your alternator is oscillatiing.

 

For anyone interested or following this thread I'll post an update. I drove the car yesterday and the flickering was back and the voltage varied from 14 to 15 volts. I disconnected the alternator connector and all the flickering stopped and the car ran great just off the battery. I went and picked up a new regulator ($25) from NAPA and a can of electrical contact cleaner. The inside of the alternator was pretty dirty and it looked like there may have been some rubbing between the stator and rotor. I cleaned everything thoroughly and installed the regulator after verifying my diode trio was good with my meter. After putting it all together I noticed the alternator shaft has a slight wobble but could not feel any dragging when turning. I was afraid it may drag when the belt was put back on but I went this far so I figured I would try it. Took it for a 2 hour ride and there was no evidence of any lights or dash display flickering and voltage was initially 13.9 volts for the first 15-20minutes but then steadyed out to 13.5 to 13.6. I'm going to call this a victory for now but with a possible bent shaft or failing bearing it may only be a short lived victory with an alternator replacement in the future but for now I'll take it! Thanks to everyone who provided input. Mike

 

Another satisfied customer!

 

Thats great!! Sometimes catching the problem at the right time is the key to the solution.

 

Why not go ahead and replace the brushes and bearings now, before they fail? You obviously have no fear now of getting into the guts of an alternator, and there's nothing scary in there anyway.

Be well,

SJW