Inconsistent Battery Voltage

[xjokux]

I've been googling on this through mainly the DSM forums. The issue is I'm getting low voltage not consistently. The alternator will charge a bit after its been revved after 3k, I believe that when the alternator gets excite and charges and eventually drop down till revved up.


On a good day on warmed idle 13.5-13.1v, with the fans on it will drop down to 12.9-12.7v

Bad day will be 12.9-12.7v and as low as 12.5-12.1v with fans.

WOT highest is 12.9v worse I've gotten is 11.1v

Car off battery is 12.9v

I have a few gauges on the dash - battery, oil pressure, boost, boost controller and wideband directly connected to ignition.


I've changed the alternator twice so far. Added more grounds to bare metal from gearbox to chassis, alternator to block and chassis, block to chassis, inlet manifold to chassis. Added another positive from alternator to fuse box. Battery is in the boot as well with a 2 grounds to chassis.


I got the battery checked at Battery world where I purchased it. Battery World closer to work say it's on its way out, putting out 330cca instead of 450cca, and will have trouble holding charge. Another location says its good near my home where I originally bought it. This is a 3 year battery.


Question I really got is to determine whether its the battery or alternator. Both item are expensive and really don't want to purchase both. I leaning towards battery but I don't want be wrong and have a new battery. I'm hoping it's not the alternator because it's a mission to remove it. Other theory is the alternator is oveheating having a 3" dumpipe few inches away from it.

 

[Benzo4gT]

I would guess it's the Alt, it should be putting out 13.8-14.3 irrespective of what the battery is doing. Where are you measuring the volts from?

It sounds like it might be the regulator or more specifically the brushes, I've had similar issues before with another car. A good auto elec should have brushes for a few $, then you need small hands and a decent soldering iron

Here are some pics I took a while back that might be helpful if you decide to check or replace the brushes

 

[xjokux]

I've gone through two "new alternators" but I will look into it.

 

[4piknup]

I would have said brushes too.
I dont know how to test it, but you should be able to test the exciter/field voltage. If you can test that while its not charging properly, that will indicate the regulators efficiency.

Is the alt light on slightly when its not charging properly?
You might need a dark garage or night time to see it.

Is there a difference in b+ alt post and battery voltage when its not charging?

 

[4piknup]

http://www.freeasestudyguides.com/alternator-full-field-test.html

if you can work out how to do a full field test, that will help, and test the regulator.
they are talking about a variable voltage altenator in link. You earth the wire to the ecu in that case. But im not sure how to do a internal regulated one.

 

[xjokux]

Battery light is on it that is what you meant?

I'll have to compare the B+ and battery when I get home. Will there be much difference from the voltage from the B+ to the fuse box in the engine bay? I've measured the fuse box voltage. Reads 12.9v but 14.5v after revved up

 

[4piknup]

Yes. Battery light. It will prolly be on faintly. And get brighter as you add load ie. Fans, demister, lights.
you should be chevking output with as much load as you can.
there should be no difference in b+, battery and fusebox voltage. You could test with neg lead on battery+ and pos lead on b+. That would give you volt drop. You want 0v volt drop. Any volt drop is a problem that needs fixing.

Because its intermittent, it will be hard to figure out.

id still put new brushes in , they will be $12-15. I got them from autronics last time. You can file them to fit if they are too big

 

[CLuTZ]

Battery

 

[xjokux]

Key off:
Battery - 12.7
Fuse box - 12.7


Ignition:
Battery - 12.2
Fuse box - 12.5
Ecmlink - 11.4


Engine on (no load):
Battery - 14.15
Fuse box - 14.20
Ecmlink - 13.5-13.3


Engine on (with max load):
Battery - 13.94
Fuse box - 13.97
Ecmlink - 12.5-12.1v


The readings I've given to earlier were from Ecmlink directly since I can log it. I haven't turn the car on since Tuesday afternoon where the voltage was nowhere near as good as today with battery light on. Just by observing Ecmlink is alot lower than voltmeter? I'm no Ecmlink guru so I can't explain why, would this be ecu problem or ecu grounds?

On wot runs it creates knock on full boost where voltage drops

 

[evo-gsr]

Battery

+1

 

[xjokux]

+1

Why do you super battery?

 

[xjokux]

Sorry suspect, damn auto correct

 

[evo-gsr]

From everything you have posted.

 

[Benzo4gT]

What size is the + cable from battery to starter/main fuse?

 

[xjokux]

From the boot to engine, it's a 1awg or 2awg. Starter (stock wire) is connected to that along with stock wire that goes directly to fuse. From the fusebox is the orginal 2 white cables + new 4awg to the alternator.

 

[BYBY5L]

Im just gunna throw it out there even though yours may be battery and this is probably not your issue but is cheaper than alt or batt,
But after changing my batt to the boot I had troubles with high rpm misses, any psi over 15 it would miss, batt would intermittently take charge (or not take), would be hard to start (like a dead batt click) to the point I changed 2 solenoids and starter motors, an alternator, main batt cable to a copper wired one, coils and ignitors galore...
Long story short, in addition to the 2 on the rails in the boot, I ran a 2ga earth cable to the fire wall and ran 5x 4ga earths (3x to the engine, 1 to each rail) and it fixed all my problems, if ya have a spare cable it might be worth a try, cheaper than a 3rd alternator or a new sealed batt

either way, check for voltage drop and resistance in ya earth and power, it'll give ya more idea

 

[xjokux]

What do you mean by rails?

I drove car in today to work to get a new battery see how it goes. On the way the voltage was being jumpy. I've logged it so I'll post the values up soon.

 

[xjokux]

During highway driving 90-100kph

rev cycling between 2600 - 3000rpm

the voltage will jump from 11.3 - 13.3

6 times over a duration of 1.30mins

 

[BYBY5L]

Chassis rails,
Have a google on checking resistance and bad earth stuff, plenty of simple tests with a multimeter that will help ya eliminate or identify potential problems. Doesn't cost ya anything too

 

[CLuTZ]

One thing I have learnt after owning dozens of cars is that batteries can sometimes do weird shit. Even brand new ones. If you can get your hands on another battery I would try it out.... beats the hell out of swapping out an alternator!

Also check the condition of the Fusable Link in the engine bay fuse box and make sure it's the same amperage that's on the lid. It's the big fuse with see-through cover that sits in the corner of the block and is bolted in from underneath. 10mm from memory.

If those don't rectify your issues perhaps you might want to look at your MPI Relay and even perhaps your ECU.