Loss of battery voltage when running things

[suprra_girl]

Hey ya'll

I noticed last night some charging issues. If it continues this way i think i'll end up shagging out my 100amp stock alternator

The alternator is charging fine but it is having trouble keeping up with the things i have running.

It was 14 or so volts when i started it, no accessories on other than my stereo and stock digital dash and turbo timer (which has a voltmeter). Turn headlights on and voltage dropped to 13. something, drive to gasso and it charges fine 14.5v, sitting in the car park i noticed it dropped down to 12.7, turned my headlights off and i gained only .4v or so. Drive away from gasso and charging again at 14.5v. Pull in the driveway and by turning off the stereo, headlights then fogs i'm only gaining .v like .2-.5. I suspect this has something to do with the slightly rough (can just tell idle is down).

The first thing i noticed was when i was leaving i started the car according to my prosport gauge i had 70psi of pressure, by turning on the headlights oil pressure when down to about 65.

I have a relocated battery, using 2g cable from batt to starter and using 4g to fusebox and using stock cable to alternator.

Am i just losing voltage to the fusebox section or is there not enough current in the whole system. Any checks i can do?

Thanks

 

[IJ.]

Where does the battery ground?

 

[suprra_girl]

My battery grounds on the strut with clean washers and bolts for good contact. My grounds are uber uber good, tested with a multimeter from battery to a ground point in engine bay and was 0.00, checked random bolts up there too and they're well grounded also

 

[IJ.]

Chassis is a really crap ground path Suze.

 

[Yellow 13]

Isn't it supposed to ground to the side of the block IIRC?

 

[suprra_girl]

i have the main block ground, and another ground and a ground on the head. The battery seems to be travelling through chassis ok as i tested directly from battery terminal to front and tested a bolt and engine, manifold, throttlebody, cam covers and all are grounded very well.

 

[IJ.]

Hook your MM up at the starter and see what sort of V drop you get while cranking......

Trust me on this the chassis is a CRAP ground path even more so in a car that's had a lot of body work and rust in it's past.
(a hint would be electricity doesn't travel through the metal in a wire but along it's outside that's why fine strand cable is better than coarse strand)

 

[suprra_girl]

Remind me how to do that again LOL

So a couple of things i noticed about this problem, when driving charging is perfectly fine = 14.3-14.4v. As soon as the car shifts to 2nd coming back down to idle the voltage will start dropping to 12.7 or so, sitting at idle it continues to fall in increments. While driving if i turn the hazards on (to thank someone for moving over etc) my full beam light flicks on and off instead LOL I don't think my hazards are going but i don't think the headlights are full beaming but then i'm driving at the time so i ain't gonna have a look lol. When parked at idle hazards work fine, now that's strange, the least it could do was do it permanently lol

 

[osama1234]

If there wasn't such an issue before you relocated your battery, it makes some sense it was caused by the recent work done on the car
It sounds like the alternator isn't charging properly, either the alternator is messed or the wiring (in your case the grounding). I had a recent issue with alternator, and the warning lights are easily able to tell when alternator is giving issues. So again, i'd bet it on the grounding.
*if its not a lot of work, you could move the battery back, and see if it works fine. That would definitely rule out the alternator then*

 

[IJ.]

Suze: One probe to a good ground the other to the Starter + terminal then have someone crank it (might be an idea to pull a fuse so it won't start)

Watch what V you have sitting then cranking.
(this will be a good indicator of how good your chassis ground path is)

Most times GTE owners can get away with it as the motor is a low come 3.0L so there's not a lot of load on the starter.

I learnt my lesson with a 7.0L 12.5:1 Comp BBC..... :nono:

 

[osama1234]

@IJ: wouldn't the voltage sag naturally from the current draw. I am just thinking about it for the sake of me knowing perhaps in the future when my car gets moody.
I figure what you're suggesting is that having a poorly grounded car would result in a high resistance and therefore a voltage drop would occur across the ground (in her case the chassis of the car) when current tries to flow from the battery plus to starter and via ground to negative of battery.
The thing i dont understand is how do you distinguish this voltage sag from the 'normal' sag caused by the battery's internal resistance ('the normal sag'). Or would having a poor ground result in a significantly larger sag than the usual voltage drop when cranking?

(btw: sag = my slang for voltage drop)

Thanks.

 

[IJ.]

It "shouldn't" drop/sag that much on cranking.

From memory I see a 1v drop on a charged battery.

Forgot to mention you want to take 3 readings

1: Battery voltage at the battery.

2: Voltage between the block and Starter + terminal

3: Same while cranking.

Write em down and post em here.

 

[jetjock]

Battery volatge during cranking shouldn't drop below 10.5. 11 is typical. The ECU doesn't like to see less than 11 at the connector.

True voltage drop testing is done under load using both meter probes on the same path but downstream of each other. An example would be between the battery negative post and the negative clamp, then working your way along the path. Or jump ahead and go between the negative post, engine ground, alternator case, whatever. Anything more than 200 mv should be corrected.

A valuable technique, the method works on any circuit both positive and negative and across any connection. It's the best way of finding high resistances in low voltage medium to high current circuits. By high I mean a few ohms or less. The circuit under test must be loaded to get accurate results.

She should also test for ripple from the charging system. Lacking a scope the best way to do that is to use the AC mv scale. There shouldn't be more than 500 mv or so.

 

[CRE]

Did non-USDM MA70s get 100A alternators? I know North America never had anything but 70A and 80A.

 

[IJ.]

CRE: 70/80 here as well

 

[suprra_girl]

Mine is the 100amp alternator

Now after analysing my car a little bit over the last couple of days i have started pointing towards two things.

The regulator in my alternator is dying and/or i have a ground missing in my digital dash. I get no emergency lights on the dash while driving, I kinda know what charge lights look like. I Checked the digital dash tsrm and it appears the headlights, hazard & horn all use the same ground in there. Im still not sure if thats the cause tho.

I'm only getting the voltage dropping at idle, whenever the hell it feels like, for the last two days it was perfectly fine and out of the blue it will just decide to drop lol... grrr non consistent problems! lol

I'll do those tests today Ian

Jetjock, i knew there was something like that but i couldn't remember how it worked, thanks for the refresh

 

[osama1234]

So you said you got no warning lights when driving, but you didn't mention if you get warning lights when idling.

Which lights do you get, if you get any. I was having similar things, mainly at idle, and i got 3 lights: charge, bulb burned out, handbrake. The problem was fixed by replacing a chip inside of the alternator. So it was the alternator's fault. Maybe you're in the same boat.

 

[suprra_girl]

I have NO emergency lights, driving or idle... did you read my post about the regulator? Regulators don't cause the charge light to come on, did your high beam light flick on and off with your hazard switch too?

I dont think its wiring related to the relocation, I don't know if you have read any of my build thread but I have done a hell of a lot more than relocating a battery

 

[suprra_girl]

It "shouldn't" drop/sag that much on cranking.

From memory I see a 1v drop on a charged battery.

Forgot to mention you want to take 3 readings

1: Battery voltage at the battery.

2: Voltage between the block and Starter + terminal

3: Same while cranking.

Write em down and post em here.

Been running the stereo for a good 4 hours haha

1. 12.7

2. 12.6

3. 9.8

 

[IJ.]

Suze: I'd try 3: again with a couple of jumper leads hooked between the Battery Neg and the block and see if it picks up.
(I'm surprised it starts at all at 9.8v, these may be Gumby tests but it's showing an issue)