Voltage jumps

[85HOT-T]

I tried to do a search but no luck. Any ways, my voltage will drop to a couple volts and back up to 13. I cant figure it out, and it will not do it all the time, but it is getting worse. I was thinking maybe a short in the rectifier in the alternator, or the voltage regulator. The battery is only a year old so I dont think it is it. The wierd thing is I would think the car would stall but it doesnt. The voltage gets so low that my head lights get so dim I cant see the road. Well any ideas let me know, thanks.
Matt

 

[skostur79]

if you loading up the alt at idle thats normal to a degree

have you checked the alt with a load tester

to see how many amps it puts out
?

 

[85HOT-T]

No I havent load tested it. It just started to happen two days ago. It isnt a load on the alt. It is going down to a couple of volts then jump back up then fall. The thing I dont understand is that the car should not run on less than probably 9 volts, right. It is too wierd.

 

[steve hughes]

Don't know if the alternator and the wiring to it is the same on an 85 as the 86-87's. On the late gn's the brown wire going into the connector on the alt. has a habit of the wire breaking inside the insulate. Best thing to do is take the alt. off the car and have it tested first. If it's good check your wiring carefully.

 

[85HOT-T]

Checked the alt today, good news its bad. Seen it on the machine, doing the same thing I was describing. Charges, nothing, sharges, nothing. Was kinda surprised too price is 90 bucks. I just have heard of a lot of people saying the alts they get are for n/a cars not turbo. lets hope its the right one.

 

[85HOT-T]

Ok now im stumped. I still have the problem. This sucks. Although my alt. output is higher now with the new one, but man this problem is killing me.

The voltage drop is most noticeable when you shift gears, from park to reverse, ect. I think it may be a wire rubbing when the engine moves from the load and unload. I wiggled every wire on the car while a friend watched the voltage. I simulated it once for a split second. What I did was wiggle the wire harnes behind the drivers side valve cover. I tried it many times after but nothing. I wiggle the wires to the started no luck. I think I hit every wire on the car, and no luck.

So does anybody have any ideas what is happening, or similar senearios. What is the best way to track something down like this. I mean this is so annoying, I am tempted to pull the fricken engine and trace every single wire one by one. Probably not the best idea, but man, this is rediculas.

Hope someone can guide me in the right direction, and thanks to everyone who has already posted. :smile:

 

[85HOT-T]

Ok now the situation just got more wierd. My tach will jump, but mostly sits at 100 rpm (stock led type) the boost part is fine. I think there is a loose wire behind the radio. I pulled it and wiggled some wires and the scanmaster dropped to 0v a lot. I dont know if this is emc related now or what. This is just driving me nuts.

 

[85HOT-T]

Nothing, no electronic professors here? The thing that is bugging me is the tach. I dont understand why that would be doing that. All this just started happeneing within the last week. Wierd thing is that when i move the gear selector key on/engine off it will drop voltage too. All i have to do is move it a mm. I dont understand. Its like a nightmare :frown:

 

[suicide six]

Check wiring at alt backside,disconnect tach see if this helps.

 

[85HOT-T]

well its a new alt. So should I check the field charge or the output wire?

 

[suicide six]

Id check everything.Does alt light in instrument pnl work?Are you sure autopart alt is good?What happens when brake is pressed.whats the reading?

 

[85HOT-T]

lights on blower high its like 13.6 or something

 

[suicide six]

I know you said battery is only a yr old,but Ive had new ones last only weeks.Can you try another without actually buying one?Car have any starting issues?Nothing able to hit at that area? Battery cables show any sign of corrosion?

 

[85HOT-T]

I took the cables off and cleaned, though they were not really coroded. The only thing I can think of is a wire shorting, but cant figure out what would cause everything to short. i traced the alt wire, but nothing. I might have to disonnect the starter wire and trace that.

I mean everything looses voltage. Headlights, interior lights, guages, scanmaster, radio, everything.

 

[suicide six]

You would think that all those items effected that if it wasnt a big dia wire that it would be at least be bare by now.A batter w/an internal short even at times would do this.

 

[85HOT-T]

wierd thing is when i wiggle wires behind the radio the scanmaster shorts out. But i didnt check the light, darn. But those are small gua. wires.

 

[suicide six]

Check all tap ins behind dash that you have done since owning car. Look at areas where wiring goes thru firewall.If tranny was replaced recently,check that wiring wasnt pinched during mate.Not sure if your yr car is the same as the 86/87s,but there is a grd bolt at passenger head back side.between firewall and head that always backs out and can touch firewall if loose enough.This bolt can be touched from up top but tightened and seen better from undercar looking up.

 

[85HOT-T]

I have an 87, is that dround on the head or the firewall? I did recently replace the trans about 3 weeks ago, ill check that.

 

[suicide six]

The grd is on the head itself,just below valve cover.There is a group of grds at that point.Like I said its hard to see from up top.smaller hands may be able to reach it atleast to see if its tight.

 

[85HOT-T]

hmm. i dont remember seeing one. ill have to chet tomorow.

This problem is so frustrating its crazy