'97 Auto

Ya know, I started by searching the archives, but I can't even figure what to search under for this.

All of the time, day or night, when I'm at idle especially, my electrical system 'pulses' every five seconds, like clockwork. You can even hear the engine sounding like there is a 'load' on it for a split second when it does it.

These videos are from tonight with my Treo 650 in the dark so the quality isn't that great but you can easily see what I'm talking about.

Any idea where to start?

I've sat there with everything turned off, only the engine running and it still does it in broad daylight. Very strange.

(Quicktime Movie)
From Outside

From Inside

Thanks,
Shayne

 

First thing I would check it the battery connections. Something similar happened to me with my interior lights pulsing and sure enough I had a loose negative Battery terminal.

 

This is just a guess, but most "all emcompassing" electrical problems I've seen involve the alternator. I'd get it checked out. Good Luck.

 

I had this exact same problem, I have a 97 auto as well. I thought it was the alternator as well, turns out my alternator was ok, but my battery was getting ready to take a dump. I replaced the battery and no problems since...

 

Automatic C5's come with a special clutch on the drive pulley of the alternator. Never really figured out what it's for but it is there. The clutch could be bad.

Some other things that I have found out that you should know!! What ever you do, DONT install another alternator!! Get yours rebuilt! There have numerous cases where C5 owners have gone down to their local auto parts store and handed over their alternator for a rebuilt one and have had SIGNIFICANT problems.

If you want secifics on this problem, you will need to speak to Evil Twin. He is the resident Forum GOD on alternators and knows a LOT about them!! If it comes down to an alternator issue, just have aa alternator/starter shop rebuild yours. There is a lengthy forum post on this subject.

Here are some things to check:

With a digital volt meter, measure the voltage at tha large red output terminal on the back of the alternator to ground. See if the output voltage pulsates at the same frequency.

Remove both battery terminals and clean each one with a wire brush.
Spray some brake parts cleaner in the terminals to flush out the corossion and then flush them out with WD-40. Tighten the terminal bolts in place with a torque wrench to 11 ft/lbs.

If you have a 97, I would be willing to bet you a cold one that you also have dirty corroded chassis grounds. I strongly recommend cleaning every chassis ground terminal before you get too deep in replacing stuff. Cleaning grounds is free if you do it yourself and for the most part you will see improvements.

I had a 98 MN6 coupe that had significant ground problems. I was ready to burn the thing!! Cleaning the grounds solved all of the problems!

Here is the link to that post:

http://forums.corvetteforum.com/show...ion&forum_id=1

There is one other thing that will cause pulsations in the electrical systen and I have saved it for last because it is the most probable cause of your problems. Your fuel pump cycles on and off to meet fuel demands of the engine. When it cycles it draws a pretty good load. If it is is not grounded to the frame properly Chassis ground G-401, it can cause the issue that you are having.

G-401 is on the drivers side frame rail. Look between the aft side of the rear tire and fender well. The ground connection will be a stud on the frame. Here is a picture of the area:



I broke my stud off by accident and replaced it with a self tapping panel screw.

If you have never changed your fuel filter and it is very dirty, it will also place a heavy load on the fuel pump.

Give all of this a try and PLEASE let me know how you make out!

Bill C

 

congrats on the videos. Without them, I would of found this "rythmic" pulsation hard to believe.

I agree with the others (possible bad battery), especially with the video showing the DIC. The voltage is dropping way too fast, the alt kicks on hard and brings it back up... but too fast. Then the alt seems to almost turn completely off again.

This can be easily verified by using a set of jumper cables onto another known-good car/battery. If it stops the pulsation - then it's the battery. This test is only valid though if connecting the jumper cables is done from terminal to terminal (not placing the negative cable on a metal ground source).


.

 

Yeah, I was ready to go and dump some money into a new alternator, but then I got it checked at 2 different places and the alternator was doing its job fine, both places showed lower voltage at the battery. Good luck chasing the problem down...I know how ya feel.

 

I agree... Also, I bet if you increase the load on the battery, you could increase the pulsing frequency...Turn on the radio, High beams, A/C and Fans on high... I bet the frequency goes to a shorter cycle....

 

Thanks for your replies guys. I will try everything you suggest here and report back on what I find.

Thanks!
Shayne

 

While I was out yesterday afternoon, decided to get my battery checked. I had it checked at two different parts stores. One parts store said I had 13V the other 10.5V. I thought strange. I just didn't want to get stranded by a dead battery.

I took it home, put it on a charger, then took it out yesterday night to see if it was better. It seemed to be. Stopped at a gas station, started up just fine. Went to Albertson's and when I came back to start it up it was dead as a doornail. DEAD BATTERY! Ahhhrgh.

So who else sees me but the mustang parked a few down from me, asks if everything is OK. "Do you have jumper cables" my bruised ego asks.

He tried to jump the car and it would only turn over once and die. That's how dead that battery was. Wouldn't hold a charge at all. I took the battery out and the guy with the stang offered me a ride. Who was I to argue, he seemed cool enough So down to the parts store and had them test it again. 10.2V and then when they put a load on it, it went down to 0.2V! It wasn't even enough to light the interior lights, seriously, let alone the dash.

He drove me back and I put the new battery in, all was well. I went back to the parts store and had them test the battery and the alternator. Both excellent condition. Alternator putting out 65A or so, I believe it only takes 45A to run everything full blast.

I bet that pulsing condition was as some of you mentioned, the alternator trying to charge a non-charging battery again and again, on and off and on and off.

SO if anyone else has the pulsing condition, beware, it could be the pulse of your car about to go into defib.

Thanks guys,
Shayne

 

Just fixed my vette, pulsing dashboard, fixed by tighting ground on battery and replacing side running light, 3175 bulb.

System is really dependent on ground. Burnt out bulb might have been shorting to ground also and causing a large current pull.

 

Call Ghost Busters