Intermittent Elctrical Power Issue
 

Hey there,
I am having a tough time diagnosing why my car will intermittently start.



What has been happening is occasionally when I go to start the car I get a simple click, and then all electricity is cut off to the vehicle. No dash lights, no interior lights, no beeps. Sometimes I can leave it for a moment and it will miraculously start.
I replaced the battery 3 weeks ago and the issues went away but they are now getting worse. The odd thing is it can always be boosted back to starting.


This morning the car started immediately without issue. I checked the battery with a multi-meter and it read 12.36v before starting, Around 11v during crank, and at about 14.4v while engine is running.

Indicating that the Battery, alternator and starter are all fine.


I stopped to get gas,filled up, and when I go to start the car it the tach moves the needle to 4k and loses ALL electrical power. I cannot force a single dash light to come on. I got back out measured the battery and it was at 0v I waited 30 seconds and it was back at 12.6v but still wouldn't start. I hooked up a booster pack and it started without issue.



Any help would be greatly appreciated.

It sounds like you have a draw somewhere.

Do this:
Disconnect neg battery cable.
Set multimeter to check for DC amps.
Test from neg cable connection to neg battery terminal.

You should be drawing milliamps.

At that point you can start pulling fuses to see which circuit has the draw.

14.4 is not a sure test of an alternator. It could not be putting out enough amps to charge or could have an internal short that is pulling the battery down when the car is not running.

What is the appropriate amount to draw?
I tested last night and got .34

That’s fine.


Sent from my iPhone using Tapatalk

If not parasitic draw can you think of anything else to test or try?

Clean main ground, check for corrosion on main battery connections.

If that does not work when it is not cranking check for voltage between battery negative and chassis. This will tell you if your ground connection is poor.

The issue when the battery was reading 0v does not make sense, unless the battery has an internal poor connection.

Okay great thanks I will check the grounds.

When I measure from the Negative terminal to the chassis what should I be looking for on the meter? Is any voltage bad or is there an acceptable amount?

Yes the battery is confusing me greatly as well. I actually tried cleaning the terminals first. Now oddly enough the one time i did this the car would not start, then I cleaned the terminals and it started fine. That was 4 days ago. Can enough corrosion build in that time to cause an issue?

So I am having a difficult time determining what is the "Main Ground"
The electrical diagrams has like 30 ground points.
Which is the main one?


Another thing to note is that when it cranks it starts perfectly.
The issue is getting it the electricity to crank. Does that make checking the ground from the terminal pointless?

During cranking my guess is a couple of volts would be acceptable. If you are measuring it when everything goes blank and it is the culprit you will have 10v or so measured across it.

You should not have more than a few hundred mV between the engine case and battery negative post while cranking.

Yes it is probably calculated at around a 2% drop. But if it is 1 or 2 volts it is not the problem he is experiencing.

If the battery is the original one, it may be time for a new one - :iono:

It's still not a valid reason to give him wrong information.

He just changed it.

The battery terminals are probably tight, but check the bolt where the negative is bolted to the inner fender on the passenger side, the main battery fuses on the B+ terminal, as well as the bolts where the cables are attached to the battery terminals, as well as the bolt connecting the B+ to the underhood fuse block.

Pay attention to the two fuses on the B+ terminal, I've seen some blown ones that *barely* made contact and made for some intermittent issues. If that is what has failed, don't try to rig something, that's a recipe for getting stranded.

:bellyroll::bellyroll::bellyroll: