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Discussion Starter #1
After returning from vacation after a week, my car refuses to start under it's own power. Sure, it starts and runs once it has a boost, but I seriously think it's the battery. Funny, the car is only an 07 with 70k on it.

After the car is running, the idle is rough, and there are random clicking noises as well as dash lights popping up randomly when driving.

When putting a volt meter up the the battery when it's not running, I get a reading of less than 10v, running it's b/t 13-14v

Can someone please confirm it's the battery?

thanks :)
 

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7 years on a battery ain't bad....

And yeah, if it's only showing 10 volts after running (engine off) the battery's likely shot. (90% certainty at least, any battery can show low after start & before it recharges - 10 is very low)

Fully charged battery needs to maintain a MINIMUM of 9.6 volts when cranking, your own "load test" of watching battery voltage when cranking after charging the battery would give absolute proof. Even without charging it more (if you don't have a charger handy) watch voltage when you try to crank & if it just drops down fast you know it's shot.

I'll move this to General tech Chat for a better location.
 

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Vince your Moderator
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I agree with Sailor,

New battery time. If it's at 10v, it will never hold a good charge again. Several group sizes will fit in it's place.
 

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Discussion Starter #4
yup, got a new battery and she's alive and running again. the funny clicking noise under the dash is gone too.

Considering the alternator commonly goes on these cars, would it be a bad idea to keep one on hand, just in case (more likely WHEN it fails) which should be soon? at least it's a bit of cheap insurance.

Does the wiring harness that leads to the alternator also fail due to the high heat location?

thanks in advance
 

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Vince your Moderator
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Yes and yes.

Have a local rebuilder rebuild one for you.
 

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Discussion Starter #6
I'm looking for one with lifetime warranty. Not sure if a rebuilt one from a rebuilder would get the same guarantee.

Funny, the alternator on my 88 bmw 325is was last replaced back in the late 90's sometime with a rebuilt one. Still kickin strong
 

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Your last comment is why the local rebuilder option is mentioned so often here.

Better quality job of rebuilding, many "Lifetime" units aren't worth the hassle of changing them regularly.
 

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Vince your Moderator
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13-14v output is not that good.
 

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I have an 07 with >85k miles, original alt still running fine. These are the tests I routinely run:

ROUTINE VOLTAGE CHECKS:
- Check resting battery voltage, optimal is >=12.6 Volts

NOTE: By resting I mean the car has not been running for 4 hours

- Check charging voltage 13.5-14.5 Volts with all accessories on and engine at at 1200 RPM

NOTE: All accessories means anything electrical (high beams, radio, wipers, rear window defogger, ac on and ac blower fan on high, flashers on, turn signals on, etc.)

- Check cranking voltage (>= 9.6 volts)

NOTE 1: You want to be able to crank the engine without the engine being able to start. On some cars if you floor the gas pedal and turn the key to the crank position, the engine cranks but the engine will not start because the fuel injectors are disabled. On some cars you may have to trip the fuel cutoff switch or pull the fuel relay.

NOTE 2: I use a meter that has a "minimum voltage" setting. This functions holds the minimum voltage measured.

So I hook up the meter, disable the fuel, crank the engine for 5 seconds, then record the minimum voltage.

These basic tests answer the questions:
Does the battery hold a charge?
Can the alt charge the battery?
Can the battery supply adequate voltage while starting the engine?
 

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FYI, the number I spout all the time of 14.0V minimum charging at idle is with NOTHING extra on, so seems to fit.
 
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