Pulsing Lights/Headlights

[CamaroCrazyChris]

I have an 02 Z28 Stock/automatic, 94,000 miles. Dont worry though... I got about 3500.00 worth the mods sittin in my garage ready to throw on.
Anyways... I bought the car a month ago with a pulsing light problem, After the engine warms momentarily all of the lights in the car and outside the car start to pulse rapidly, and my voltmeter starts going crazy from 12-15 volts.
I contributed it to be a cheap fix... (Alternator going bad) The alternator was the orignal so I had a brand new 240 amp Powermaster from my Silverado layin around so I decided to try to squeeze that in there.... It was a tight fit but I managed to get it in there with the removal of the rear alternator support bracket. I started the vehicle and 5 min. later the pulsing was back in full swing. With the new Alt. though it seems to be isolated at ideling but sometimes it still happens at highway speeds. I checked my pully ratio and that fine. So does anyone have any ideas on what gives???? Its like the electrical system go's into a serious amperage draw or something.
Anyways... Sorry for the long post but I didnt want to waste anyones time with stuff I already thought of.
Thanks again

[Sarge]

Sounds like a direct short to ground.....on this model....is the voltage regulator built into the alternator or is it seperate?....I'd vote on the direct short to ground first though....

[CamaroCrazyChris]

The regulator is built into the alternator, If it is a short.... Why would it only do it after warm-up and why is the pulsing so precice? Thank you for your help though.

[BorgX]

I am having the same problem... I am on my second alternator... anyone figured out a way to fix this??? Thanks in advance!

[YoMommasTA]

check the connection to the PCM carefully...be sure its hooked up and clean.

[killerbeez]

I'll join this club!!! I just bought a car and it's doin the same thing. 98z m6. Where is the pcm on these cars anyways? On my car, I noticed, if I'm running the stereo and almost drain the battery, it will stop pulsating.... for a little while. It's almost as if if the alternator is charging the battery it won't pulsate, but once it reaches full charge it has nothing to do so it like overcharges and pulsates. what's the deal?

[YoMommasTA]

I'll join this club!!! I just bought a car and it's doin the same thing. 98z m6. Where is the pcm on these cars anyways? On my car, I noticed, if I'm running the stereo and almost drain the battery, it will stop pulsating.... for a little while. It's almost as if if the alternator is charging the battery it won't pulsate, but once it reaches full charge it has nothing to do so it like overcharges and pulsates. what's the deal?
voltage regulator

[rgarrett]

same problem, any solutions?

[BorgX]

I ran a ground wire from the alternator bracket to the driver fender (already a ground there), and I have now had the same alternator, with no pulse, ever since... it's been about 6-7 months... a new record for my car. Only time will tell...

[Redphoenix1998]

check ALL your grounding straps. There is one that goes into the back of the alternator as well and commonly in an alternator install, that wire is not hooked up at all. Check it to make sure it's on and check all your grounds from the batter and grounding straps. Clean the straps as well. I had the same problem and thought it was my alternators but in reality, it was that one stupid strap

[desliger]

Sweet! I was going to post a thread asking this same question, now I know! :yup:

[rgarrett]

I checked the grounding locations on radiator support, both fenders, and the strap from the alternator. I cant see where the other end of the strap on the alternator goes, it seems to tuck in behind it. do you have to remove the alternator to get to it?

any other ground locations to look for?

[desliger]

I too have checked/cleaned every ground strap I could see, are we missing something? I'm still pulsing over here, with around 117k miles I'm thinking it's the alternator... lol I do know that the map light does not pulse with the engine off, but when I start the engine, you can see it pulse with the rpms...

[Hot Black Trans-Am]

I wonder if it could be something with the A.I.R. system opening to a ground when it is not running. You can try to pull power from it and see if it helps. Just an idea.

[ohsofast]

My brother had a similar problem, he took it to GM and they said he needed a new pcm,it wasnt cheap b/c they charge for parts then upload it then labor. But that is worst case scenario. He had an 01 SS M6 with +90,xxx.

[rgarrett]

talked to another guy with an 01 that had same problem said dealer replace alternator and something under dash before it stopped? He couldnt tell me what under the dash... I am going to call dealer he went to and see what it was. Will post if I find out anything

[rosco924]

Did anyone ever figure this out because mine does it too with 60K on a 99 Z28.

[rgarrett]

my car is at chevy dealer today diagnosing problem. dealer seemed to know about it when i dropped it off. will post when I find out.

[Steve Crowe]

As some have noted this is often a ground problem. Most cars have a decent size ground cable running from the engine block to the frame, however they've been known to break or get lost when an engine has been removed for some reason.

A good contiuous ground is important - not only to your lighting, starting etc but also to all your sensor electronics. Ideally you'll have a sort of "triangle" in which theere a cable going from the battery (-) to both the frame of the car and to the engine block near the starter, then another from the engine block to the frame.

[Hot Black Trans-Am]

I just noticed mine will pulsate when it is cold and warming up, but they are fine once the car is warm.

[rgarrett]

dealer just got back to me and said problem is coming from alternator. Will get it back tonight and see if that indeed fixed the problem.

[Toes]

Headlight switch is possible? PCM I dont think so!!!!!!!!!!!!!!:shots:

[rgarrett]

it was alternator, works fine now.

[m1lkym1ke]

Possible Solution:
I had the same problem on my 95' transam. I went to autozone and had the battery and alternator checked... all was good... But my engine would cut off, bog down, lights flicker, and I would hear a clicking sound. Well to keep it all short. After I cleaned everything and still no go. I raised my car and was looking under... One of my spark plug wires was getting eaten by one of the pumps. It was almost cut in half and was causing the short. Just remember guys, Check all your components that could cause this. There are more things then just an alternator and battery that can cause this to happen

[chuckie669]

Good thread. I took mine to the dealer about this 6mo ago. They told me that it was a common issue and nothing to fix. Gotta luv those dealers. At least they didn't charge me arm/leg to fix things not broken.

I just start my car up and anytime someone rides with me, tell em common t/a issue. blah blah....
:brick:

[kidA(somedayullnoit)]

mine started doing that after i had my subs installed, he pulled the pcm to run a cable to the rear and after that it started to pulsate and the voltage drops when im at a stop, so i figure either the amp is too much for the alternator or he nocked something loose.

[kraemer94]

I'm having the same issue. Only when the car is hot and at idle. Dealer ship replaced the Altenator and they said the problem was fixed. Wrong. It started back up the same day. I also had them change the battery cables with the upgraded ones I brought online. Has anyone fixed this problem?

[FSANE]

same thing with mine since I remember, probably since I bought the car brand new. It seems that the alternator is over charging.

[kraemer94]

Any one know how I can turn on my fans and test all speeds with out having to like drive the car to get it to turn on? I'm think one of my fans might be causing the issue.

[FSANE]

Any one know how I can turn on my fans and test all speeds with out having to like drive the car to get it to turn on? I'm think one of my fans might be causing the issue.

keep the car running with the AC on.

[kraemer94]

Well it's not the fans. Brought the car back to the dealer ship this morning. They still can not find the problem. Guy telling me it might be the PCM. I don't get it. Why it's only happening when the car is at idle for a while and the second fans kick on. O well, we will see what they tell me tomorrow....

[B34M3R]

Given the severe commonness of this problem, I have a few ideas.

Ok, first and foremost, is this occuring when you have your AC functioning??? Does it go away without it?

If this is not the case, then I would indeed suspect the PCM. It does make sense, and heres why. The PCM should be controling the voltage reg... (i think these models do anyway) if the programming in the PCM is "stupid" then it is prolly cycling the reg when the voltage is at its lowest, in an attempt to stablize the voltage to keep all of its sensors happy, rather then suceeding at keeping a constant, its dropping the ball, and bouncing around. It is a possiblity.

Heres an idea for you guys, get in there with a GM scan tool and raise your idle a couple 100 RPMs... whatever the problem is, getting the idle up to keep the voltage from hitting the low zone should eliminate it, period.

[kraemer94]

Does not matter if the AC is on or off. Also car is stock. no aftermarket radio etc.
Problem I have is when the car in idle, say waiting in traffice for a while enough for the fans to kick on. Voltage guage jumps all over. So much that I can tell it affects the engine,lights etc. But if I give the gas the voltage goes back up and once I just driving again everything is back to normal. Sounds like an altenatr problem but they already changed it and it's doing the same thing.