Pulsing lights giving me a headache

ibHenry · **Posted:** Sat Apr 07, 2012 8:44 am

Sounds like a bad ground to me. Did you clean your battery connections when you installed the new battery? If you did, I would be checking all my grounds, especially if you live where corrosion is an issue. Grounds are very important on computer controlled vehicles. A weak one will exhibit those kind of symptoms. :JEEPIN:

maxf15 · **Joined:** Tue Feb 28, 2012 1:30 pm **Posts:** 52

Billwill wrote:

geordi wrote:

Where in Georgia?

As for the problem of pulsing lights - The voltage regulation is handled entirely in the engine computer by rapidly "flashing the field" of the alternator itself - rapidly cycling the power field of the alternator on and off, and varying the input voltage in the field to make different output levels. What this means is that the alternator itself is somewhat of a dumb device, only doing what it is told and spinning along merrily... Except for the internal diodes and contacts. If you are having pulsing light problems, it is due to either a slipping clutch or a blown diode. Either one is a pain in the arse to deal with, when a full replacement alternator is $150 from AutoZone with a lifetime warranty and will, without question, solve this problem.

If the diode is the problem, wouldn't you want a fresh clutch anyway, after so many miles of spinning and clutching? I would.
If it is the clutch... Well... Wouldn't you want a fresh set of diodes anyway, since they do also go bad? Yep, I would.

Best of luck to you.

Not quite correct....if you read Keith of GDEs' explanation above you will see that the 05 upwards KJ has a regulator built into the alternator as was done in the old days...the ECU only "wakes up" the regulator.

I believe the problem is firstly the clutch on the alternator or a faulty regulator....I do not buy the idea of a blown diode in the diode pack causing the flickering....the alternator runs at such a high speed that one would not see the effect of one rectifying diode being blown.

I would also check for good earthing straps of engine to chassis and of course good battery connections.

geordi - I'm in the Warner Robins area... middle GA as we call it.

Great info from all, and thanks!

I took it to Advance Auto last week, and had them run the diagnostic test on both battery and alternator. Can't remember all the stats, but it passed with flying colors, even under load at 1500 rpm. Of course, two nights later, was driving after dark and the flickering was there again.

It is quite annoying, but not unbearable. The biggest concern is a total DC failure, and/or slowly frying other electronics (relays, switches, lights, etc) with such varying voltage.

I'm likely going to re-check battery and grounding (earthing) connections, take it for a night test drive; and if that doesn't fix it, go buy the new alternator.

Will post in a week or two what I find.

geordi · **Posted:** Sun Apr 15, 2012 12:10 am

Those testing machines are worthless, they can really only "test" if the tiniest amount of power is available in a battery or coming from an alternator. Truly loading it down can only be done by the vehicle itself.

Case in point - I had a 1000 amp battery from Wal-Mart in my CRD, that failed to spin the engine fast enough to make it start. I took it in for replacement, and was told they wouldn't do ANYTHING until it had sat in their "testing" machine for over an hour. Lo and behold, the machine declared the battery "good" and they wouldn't do anything. It spent that hour charging the battery at high rate (bad for battery life) and yea, it did start the CRD quite rapidly when I put it back in.

And the battery failed to start the CRD again 2 days later. This was after using it in the ensuing days, not like the CRD had sat for that time. Took it BACK to Wal-Mart and wasted another hour... Told that the battery was fine AGAIN, and they would do nothing.

Replaced it at full cost with an 850 amp Interstate Megatron from Costco... Haven't had a problem since.

All this was on the NEW alternator that reads 14.3 volts while running on my radar detector.

You cannot trust the testing machines. If you have a problem in the vehicle - You have a problem in the vehicle. Plain and simple.

maxf15 · **Joined:** Tue Feb 28, 2012 1:30 pm **Posts:** 52

Great point geordi. I have a new alternator on order. Found a $50 off coupon at advance auto with free shipping. Basically $100 for a new alternator with a lifetime warranty. If that doesn't work, I'll try a new battery.

In a different thread, but I think it's realted; my cruise control is knocking off by itself. I think it's all related to 'dirty' power.

Hey, on these electrical systems, does the car run off the alternator or the battery when it is running? Of course battery for start, I know. But once started, where's the primary power source? Anyone?

Thanks!

dkenny · **Posted:** Thu May 03, 2012 7:03 pm

there is another test for car electrical systems that gets over looked..

if you have DVM..you know for checking the DC voltage..
every check it for AC voltage? YES switch it to AC and put the lead on the battery..

don't be surprised if its not 0 while its running..the alternator creates 3 phase AC..not DC..the diodes convert this to DC but its not clean DC..clean as in just a battery( engine off) clean..

if you DVM has a freq measurement option you can measure the freq..ever wonder how a tach work on simple diesel engines..ones without computers, cam/crank sensors..

if a diode is failing the AC voltage will be higher..more noise. technically if the diode is open it'll be missing the pulse from that phase..if you know what a sine wave looks like..now put 3 of them together but out of phase by 120 degrees..covert to DC..this makes ok DC by the way..until a leg(phase) is lost..

does this help with the flickering? maybe..what if the diode fails under heat(or load)? is it just one diode failing?
it gets ugly if 2 phases are failing..

dkenny

maxf15 · **Joined:** Tue Feb 28, 2012 1:30 pm **Posts:** 52

dkenny wrote:

there is another test for car electrical systems that gets over looked..

if you have DVM..you know for checking the DC voltage..
every check it for AC voltage? YES switch it to AC and put the lead on the battery..

don't be surprised if its not 0 while its running..the alternator creates 3 phase AC..not DC..the diodes convert this to DC but its not clean DC..clean as in just a battery( engine off) clean..

if you DVM has a freq measurement option you can measure the freq..ever wonder how a tach work on simple diesel engines..ones without computers, cam/crank sensors..

if a diode is failing the AC voltage will be higher..more noise. technically if the diode is open it'll be missing the pulse from that phase..if you know what a sine wave looks like..now put 3 of them together but out of phase by 120 degrees..covert to DC..this makes ok DC by the way..until a leg(phase) is lost..

does this help with the flickering? maybe..what if the diode fails under heat(or load)? is it just one diode failing?
it gets ugly if 2 phases are failing..

dkenny

dkenny,

Great explanation, thanks.

I changed out the alternator with a new one, but noticed the same symptoms occurring within a few days. The new alternator did arrive in a beat up box, so it may be bad too. Murphy's law maybe??

I'll try the AC test. I have a digital volt meter. But what numbers should I be looking for? Is zero good, and higher AC voltage bad? Or is there a 'within specs' measurement? Test while running? Why not test the alternator leads?

They shipped the bench test sheet with the alternator by the way. Of course, it all looked great, but that's before UPS drop kicked it several times!

All ears...

dkenny · **Posted:** Sat May 12, 2012 1:30 pm

yes..0 is best..but 0.1-0.2 Vac should ok. yes must be running..that's when you have the pulses right?

also yes you can check at the alternator output..should be close to the same as the battery..if not somethings not right with the wire.

if you have a oscilloscope measure the AC with that..I suspect you find a pulse that matches the pulsing your seeing..
then check the line from the ECM..even if its only a turn on signal..does it turn off??

if my wife's jeep was home. I'd run out and get some real numbers for you to compare too, but its not..

-dkenny

xtriggerman · **Posted:** Mon May 21, 2012 2:01 pm

Im having this same pulsating headlights issue. I have a related story on my 01 Dodge CTD. I installed a HD alternator and a external voltage reg on it a couple of years ago. The ECM normaly controls the voltage but they do go bad. I had the same pulsating lights issue with that set up. The fix is to take the keyed power feed that runs the external VR and use it to run a new power relay directly from the battery to the voltage regulator. Apparently the VR was getting alot of dirty power out of the wiring harness that corrupts the fuse panel from where I originaly pulled power for the external VR.
If this Jeep has a external VR in the ECM or PCM, it may be possible to find the one wire in that is the VR wire and do the above "fix" by interupting that wire and feed it VIA a direct battery relay.
Any thoughts? If the new Alt, fails to fix this, this may be something to consider.

xtriggerman · **Posted:** Fri Jun 01, 2012 12:32 am

Finaly got the Auto Zone rebuilt Duralast Alternator and put it in the Jeep today. Its a pretty easy job with a couple of tips for the folks that dont do this very often. The key to the job is to not desturb the serpentine belt off the other pullies. I found that if you use a 4" C clamp on the timing cover, you can block up your 3/8ths drive ratchet with pipe extension so it holds the belt tensioner over, keeping the serp belt in a loose condition untill you are ready to slip the belt back on the new alt. I use a bungy from the hood down to the bely to hold it on all the other pullies while off the alt pully as shown here. I didnt bother to disconnect the battery, I just slipped a 3" section of 1"ID rad hose over the alt hot wire once it was off to keep it from making fireworks.

The interesting thing I found after I took the old alternator off was there was a major hot wire grounding out against the top of the dog bone bracket that holds the back of the alt. to the engine. This wire and connector were lying loosely over the bracket and up around the engine cover post. This heavy arking that was going on may have been the entire problem in the first place or had a hand in killing the alternator's smooth signal. After mending the bad wires, I wasnt about to put the old alt back in to see if the bad wires caused the flickering.

I put the new Alternator in place and I just tested it out tonight and found the problem is solved. The thing to do before you buy a new alternator like I did, is check the pictured connector for rub throughs in the indicated places. The Japs have it all over American vehicles when it comes to harness protection. This rub through should never been alowed to happen. My Jeep has 74K on it and was in mint original shape when we bought it with 65K on it so I'm sure this wire was not secured in any way right from the factory.

jrsavoie · **Posted:** Thu Dec 24, 2015 7:07 pm

geordi wrote:

Those testing machines are worthless, they can really only "test" if the tiniest amount of power is available in a battery or coming from an alternator. Truly loading it down can only be done by the vehicle itself.

Case in point - I had a 1000 amp battery from Wal-Mart in my CRD, that failed to spin the engine fast enough to make it start. I took it in for replacement, and was told they wouldn't do ANYTHING until it had sat in their "testing" machine for over an hour. Lo and behold, the machine declared the battery "good" and they wouldn't do anything. It spent that hour charging the battery at high rate (bad for battery life) and yea, it did start the CRD quite rapidly when I put it back in.

And the battery failed to start the CRD again 2 days later. This was after using it in the ensuing days, not like the CRD had sat for that time. Took it BACK to Wal-Mart and wasted another hour... Told that the battery was fine AGAIN, and they would do nothing.

Replaced it at full cost with an 850 amp Interstate Megatron from Costco... Haven't had a problem since.

All this was on the NEW alternator that reads 14.3 volts while running on my radar detector.

You cannot trust the testing machines. If you have a problem in the vehicle - You have a problem in the vehicle. Plain and simple.

I had a similar issue with a battery several years ago. I told them to let the battery sit for 2 hours and retest it. Low and behold, the battery tested bad then.

flash7210 · **Posted:** Tue Dec 29, 2015 5:35 pm

I'm working through this issue too now.
Gonna try getting a used but known good alternator to compare and test.

flash7210 · **Posted:** Sun Jan 10, 2016 8:26 am

This pulsing light problem is very strange.
Its intermittent and not a loose connection or bad ground.
Other symptoms include dimming of lights and reduced fan blower speed when letting off the throttle.
Its also not detectable with a voltmeter.
I have tried using the voltmeter and whenever I stop the vehicle and connect up the voltmeter, top post on alternator to negative battery terminal, the pulsing immediatly stops.
I think this is a clue.

Im gonna try soldering together a circuit to filter out the pulses and see what happens.

Billwill · **Posted:** Tue Jan 12, 2016 3:43 am

flash7210 wrote:

This pulsing light problem is very strange.
Its intermittent and not a loose connection or bad ground.
Other symptoms include dimming of lights and reduced fan blower speed when letting off the throttle.
Its also not detectable with a voltmeter.
I have tried using the voltmeter and whenever I stop the vehicle and connect up the voltmeter, top post on alternator to negative battery terminal, the pulsing immediatly stops.
I think this is a clue.

Im gonna try soldering together a circuit to filter out the pulses and see what happens.

Try fitting a large capacitor..as used in sound systems...across the battery or across the lights themself. :wink:

ChooChooman74 · **Posted:** Tue Jan 12, 2016 10:10 pm

Alternator replacement solved mine.

Sent from my Samsung Note 4 using Tapatalk.

flash7210 · **Posted:** Tue Jan 12, 2016 10:21 pm

ChooChooman74 wrote:

Alternator replacement solved mine.

Sent from my Samsung Note 4 using Tapatalk.

Well thats just the easy way. Whats the fun in that? :lol:

My simple voltage filter, three 1000uF caps in paralell, didnt fix it.
I suspect its the voltage regulator.
I have another used alternator Im gonna try and will look into replacing the regulator in this one.

Pulsing lights giving me a headache

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