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I THINK I HAVE A BAD ALTERNATOR

 
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Old 15 Apr 2011, 01:53 pm
musky's Avatar
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Question I THINK I HAVE A BAD ALTERNATOR

i recharge my battery ,the car will start and drive for a few hours on and off throughtout the day,but then all go back out and turn the key and nothing battery is 100% dead even the radio will not work...so i used a battery charger and put the battery back in started car,then took postive cable off the battery and the car dies instanly is it a bad alternator?

is there another way to test it....

its a 2006 pt crusier...non turbo
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Old 15 Apr 2011, 04:41 pm
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Default Re: I THINK I HAVE A BAD ALTERNATOR

The proper way to test the alternator is to do a voltage test...a good alternator will read between 13.5 volts and 15 volts at the battery terminals with the motor running. If it does not at idle with no load or if it drops with the AC and headlights on then it is bad. Taking the positive battery terminal off with the engine running is very bad for the alternator and the electronics in the car...it can send a massive spike to the altetnator and electroncis, enough to fry the diodes in the alternator and fry the computor. If you don't have a volt meter take it to Autozone and they will test it for free on the vehicle.
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Old 15 Apr 2011, 05:42 pm
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Default Re: I THINK I HAVE A BAD ALTERNATOR

Quote:
Originally Posted by azphotog View Post
The proper way to test the alternator is to do a voltage test...a good alternator will read between 13.5 volts and 15 volts at the battery terminals with the motor running. If it does not at idle with no load or if it drops with the AC and headlights on then it is bad. Taking the positive battery terminal off with the engine running is very bad for the alternator and the electronics in the car...it can send a massive spike to the altetnator and electroncis, enough to fry the diodes in the alternator and fry the computor. If you don't have a volt meter take it to Autozone and they will test it for free on the vehicle.
Autozone or Advance Auto... I have three on three corners here, Napa, Advance and Autozone. Go figure. Anyway, a voltage test does you absolutely no good (not meaning to offend) unless you have a load bank to hook it too. I can charge your battery for 5 minutes, then test the voltage and think, "hey, great, 13VDC". Put a load on it and it dies in a minute, then you know it's not holding a charge. Both Autozone and Advance Auto use a small, portable load test bank when they test your battery. Now, if your first cell in your battery is down, you can have this problem. If the last cell is down it might be similar but usually won't hold a charge for more than just a few minutes.
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Old 15 Apr 2011, 08:14 pm
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Default Re: I THINK I HAVE A BAD ALTERNATOR

This car has been in the garage every month since i bought it,never again paid 8000$ for it because the wife wanted it even though i told her not to get it ,and have put almost 3200 $ in it in 1 year.junk.

ok but even though i can mess up the computer by doing what i said ,when i take the positive cable off and it dies that says its the alternator.correct?
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Old 19 May 2011, 03:51 pm
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Default Re: I THINK I HAVE A BAD ALTERNATOR

No - most modern cars will not run without the battery being connected. Pulling the live cable off while it is running is not a test of alternator capability. Go to Maplin or somewhere like that and buy a multimeter. When applied to a battery with the engine off, the voltage should read around 12 - 12.5. With the vehilce running, it should read 13.5 - 15. It should maintain this voltage when the lights and AC are turned on (the idea being that the alternator steps up the charge rate to maintain steady power in the battery as the car needs this). If the voltage dips and does not come back up, the alternator is likely weak. If the voltage remains at the same as the 'off' voltage, the alternator is screwed.

As was mentioned - don't pull the live cable off when the engine is running or you may fry the CPU.
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Old 19 May 2011, 04:20 pm
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Default Re: I THINK I HAVE A BAD ALTERNATOR

I will add this taking the positive cable off my 1978 chevy IS a good way to see if the altenator is working there is no computor

but i would say the chances are verry good the alt is bad either the alt or the battery OR you may have a BIG draw like a dead short that is sucking the battery down
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Old 19 May 2011, 04:23 pm
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Default Re: I THINK I HAVE A BAD ALTERNATOR

Agreed. Local autoshop should be able to run a battery test for a couple of dollars - this will tell you quickly if the battery is dead or not and should also ID an alternator fault.
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Old 19 May 2011, 04:23 pm
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Default Re: I THINK I HAVE A BAD ALTERNATOR

Musky,

The car's not junk. It's not a bad car at all. Your's may be because if you paid $8k for it, you bought it used and you have no idea how the first or even second owner treated it. For that matter, if you've had THAT much trouble with it, it could be one of the cars that was totaled in some weather disaster and then taken to another state, retitled and sold as a good running car. Unless the car is gone over by a competent mechanic before you buy it, you don't know what your getting.
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Old 20 May 2011, 10:40 am
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Default Re: I THINK I HAVE A BAD ALTERNATOR

My two cents worth.
First get the battery load tested. It is cheap and easy and the first thing I would suspect. If the battery has a bad cell, it could give you everything you need except the power for cranking the engine over.

No one mentioned the battery cables. If the cables are frayed, simular issue. Check both ends especially the non battery ends.

If the alternator is bad you would probably get a alternator light on the dash.
I know that the alternator could be partially charging enough to keep the light off, but my experience is that this the exception more than the rule.
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Old 04 Dec 2012, 08:57 am
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Default Re: I THINK I HAVE A BAD ALTERNATOR

I want to correct some bad info here.

At least my 01 PT cruiser will run fine with battery disconnected. It is a great way to confirm alternator function. May possibly put a big load on alternator but I think that is an academic argument..never have seen it in real life. May be prudent to wait till ignition is off to reconnect the lead though as you never want to chance damaging computer though again...unlikley ypu would just hooking up the lead while still running.


I believe one also needs to check the green fuseable link by the starter to do a complete diagnostic.

Lastly....HOW TO CHANGE ALTERNATOR

Jack up passenger front of car and set on jack stand.


Disconnect battery then go under car and remove the wires from alternator.

Remove two top motor mount bolts that attach to engine block pass side and push mount to the side.

Remove the front bolt on the lower motor mount.

At this time you will see that the motor rocks back and forth..that's what you want.

Now Remove the pivit bolt at alternator base where it attaches to the mounting bracket.

Then from above remove the tension bolt and stud. You may need to bend the ac drier's mounting bracket a little to get the adjustment bolt free.


Once alt is free move out out of the way and remove the lower alternator mounting bracket from the block (three bolts 15mm and 13mm).


Now use jack to support engine under oil pan..LIGHT PRESSURE HERE so you don't damage pan. I would say back pass rear corner would be the best spot on the pan to jack from. No heavy pressure..just a little tight.

Now remove the center motor mount bolt at wheel well. There is a 2" plastic plug and a grounding wire there. Easy to access but bolt is a Torx 55 I think. Lift engine enough so there is no weight on that bolt and remove said bolt.

NOW ENGINE IS FREE ON PASS SIDE. If you jack up the engine as far as possible..a little scary but won't hurt anything......then you can work the alternator out and free (tight fit) between the frame, engine and out from the side by the front of the wheel well/ A-arm area.

Just reassemble in reverse. Alternator in then off to the side..re-install bracket. and so on. Only tricky part is you MUST put the tension adjustment parts loosely together on the top of the alternator first before installing the bottom pivot bolt. Took me 45min to figure this out..Like a jigsaw puzzle.



Not a fun job...but seems much better than taking the axle out and suspension apart. I did not even have to remove the wheel. No special tools necessary sans a big torx socket. My stubby flex ratchet was nice to have, but I doubt is needed if you have more basic stuff. All I needed was a basic socket set and combo wrench set. In fact I used just a 13, 14 15mm wrenches, 10mm 12 13 15 and 18mm sockets, Stubby flex ratchet, regular ratchet and a big torx socket (t55 I think)

With having TWO bad alternators in a row I can now do a complete alternator change start to finish in one hour with this method. I read some other post where I guy said he ground off a bit of the manifold and got it out that way. Thought about that and looking closely I doubt I that would have worked without freeing the engine. Considering it takes all of about 5 min to get the engine loose it was stupid to even go there. The only difficult part of this is working in the tight area removing the bracket and the hardest is holding the alternator in just the right spot while you have to reassemble the tension bolt through the stud that then goes through the top hole in the alternator. Once you get that sort of loosely assembled then you can attach the pivit bolt at the bottom. If you make the adjustment parts too tight here you can not swing the alt around and set in the right spot to line up the pivit bolt. The rest of the job is straight forward.
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