Volt meter bouncing, headlights dimming

[Finale-gt]

Apologies if this has been covered, I have searched but not found a definitive answer.

When I start my car (96 GT Auto) the volt meter bounces up and down and the headlights, interior and dash lights flicker. Whilst this is happening the revs are dipping in time with the lights.

This happens for about 1 or 2 minutes then goes back to normal.

The battery measures 12.64V in off. When I start the car it bounces from 12.5 to 13.6 ish volts. During this time the battery light is on the dash. When the revs, lights etc settle the battery reads about 14volts.

The car will then run fine until the next cold start. Any ideas on what I could check or look at please?

 

[ttocs]

under drive pullies?

 

[Finale-gt]

No mate, standard pulleys.

 

[ttocs]

sounds like the batteries resting voltage isn't bad at least at first. Did you try reading it 12-24 hrs after it was shut down? It should drop a little but a bad battery can look almost fully charged and even pass a batt test but if you let it sit it will loose voltage.

If that is not the case then its the alt or ccrm. Alts can be checked while on the car at vatozone but the best way is to remove it and bench test it. Now it might not be the hardware and could just be a connection. As normal in electronics if you do not start simple with grounds/connections the often end up being the very last thing you check 3 days later. Remove the grounds on the battery and at the chassis. You can use coke and a wore brush on the battery and sand papar for the chassis. A little dialectric grease will help kep thing from corroding so much and you can be sure they are good. Also check the connections at the starter.

So in a nut shell check all the wiring before we start to suspect the hardware is bad. Don't be afraid to get a little rough with the wires to test them. Give a good tug on all wiring, twist it and just try to manipulate it to see if while doing this you see any copper or any wires come out of the harness. its possible for it to just be pushed a hair far enough out of the harness that it may connect if your giving it gas or on the brakes and these problems are always the hardest to find and fix

 

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Thanks for the info. The battery has been disconnected for days as I just changed my motor mounts, I reconnected my battery at night then did my measurements the next morning. I had the starter motor off during this job (The problem was present before the mount job) so I know it's not the starter connections. I do have a split in the sleeve on the thick negative cable right next to the negative post on the battery where it looks a bit green but I would have thought that wire is thick enough to still make good contact.

I'll start by taking all the grounds off and cleaning them up though it's strange it only does it from cold for the first minute almost like it's caused by something struggling whilst cold.

 

[ttocs]

not really. Consider how the expansion of the metal as it heats up could cause it to make the connection it was not able to do so well while it was cold.

Now for all the lights flickering, the only thing I can really think that has access to all those would be the keyless entry module if you have one. If you do try disconnecting it and see if the flickering stops.

take a vid of this as well its hard to imagine what is going on.

 

[Finale-gt]

Basically the revs rise and drop in sync with the volt meter and the lights dim everytime the needle and revs drop.

I've just cut the green end off the battery negative cable and made a fresh connection and cleaned the chassis grounds at the front slam panel. Typically I started the car whilst filming and it didn't do it this morning. I'm not convinced it's fixed as I drive it for an hour last night.

I've just parked it up for the week now and I'll see what happens on Saturday morning after sitting all week. I'll post back then. Cheers, Mart.

 

[ttocs]

if the end of the wire had started to corrode and turn green there is a very good chance that is your source or at the very least a spot of resistance in your wire that would effect everything in the car hooked to the battery. But throwing a volt meter on the battery as long as it charged it would show normal.

 

[Finale-gt]

Ok so I've been down to start the car today. It's still doing it, here is a video. I pull the fuel pump fuse at the end to see if it's the pump causing it but the car cut out straight away lol.

https://youtu.be/wecIPTxT1Xs

 

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The problem is accompanied by a whine which can be heard under the hood, I also noticed that the pulley tensioner was moving up and down. Unfortunately I thought I was still recording but my 10 year old had stopped recording.

Surely the tensioner should remain tense? Is this my problem? Cheers.

Mart.

 

[Finale-gt]

Bump!

 

[Finale-gt]

ok so I swapped out the tensioner pulley which made no difference at all so I took it to an Auto Electrician who is known to be an alternator guru, he swapped the voltage regulator and it is now fixed.

Thanks for helping me out TTOCS