Charging System Questions
 

Hi guys,

Background: Car has only 2000 miles on it, Roush 402R

Car won't start. Gave it a boost and drove car a couple of miles yesterday and guage in car showed fine for half the trip then dropped to maybe 4 volts for last half of trip. When I parked it and shut it off, it then wouldn't turn over. Multimeter guage shows the battery at 12 volts (quite sure it's not the battery).
1. If battery doesn't have enough juice to turn it over, how does it show it at 12 volts on the meter (just curious)?
2. If belts and connections are tight and clean what other than the alternator can it be?
3. Are odds low that it's the alternator with only 2000 miles on the odometer or is that irrelevant?
4. When I get home tonite and check the meter with the car running and it shows less than 13 volts does that mean it's the alternator or can it still be something else?
5. How does a newbie check for things other than the alternator, with a test light?

Just getting back into the mechanic thing after many years. Thanks for your help and suggestions.

Check the ground connections on the battery and on the frame back by the battery. Actuall check the cable ends too. 9 times out of 10 that is the problem.
There is also a ground connection up by the starter from the engine to the chassis.
A quick test when the car won't start is to just take a jumper cable and connect one side to the "-" side of the battery and the other to the chassie somewhere...If the car then starts you have a bad ground somewhere..
To quickly check you charging:
Assuming you still have the firewall mounted starter solenoid installed, Take your volt meter and check the voltage on the right side (drivers side in USA) of the solenoid. (It's always HOT) while the car is running, should be around 13.8 volts.

[quote=Blas;931971]Check the ground connections on the battery and on the frame back by the battery. Actuall check the cable ends too. 9 times out of 10 that is the problem.
There is also a ground connection up by the starter from the engine to the chassis.
A quick test when the car won't start is to just take a jumper cable and connect one side to the "-" side of the battery and the other to the chassie somewhere...If the car then starts you have a bad ground somewhere..

Hi Blas, thanks for the response. Wouldn't all of the above be eliminated since the car fires up right away with a boost?

Also, if the solenoid checks out ok and the battery's ok, would that mean that it's the alternator (if it reads below 13 volts) for sure or just mean I'm closer to the answer?

Just pull your alternator off and take it to Advance,NAPA, Autozone or O'Reilly and have them check it for free. I went thru two alternators last year one on the Cobra (about $100) and one on my wifes MB (about $700).

Clois

You are not really checking the operation of the solenoid, you are checking the output of the alternator without using the Smiths dash gauge...so now you would know if your charging system is working properly...

When you give the car a boost, what are you connecting to with the jumper cables...The batteries?
Aren't you actually running a new ground and power from the booster battery to your car?

When you use the jumper cable as I mentioned, you adding a new ground to your battery. If it starts, you have a gound problem on your car's battery...

Update:
Just checked the solenoid while car's running and it appears to be right around 14. Check.
Put multimeter on battery while car's running and appears to be right around 14. Check.
Put multimeter on battery with car shut off and it appears to be at 11. (I originally thought the increments on my meter were in "2s", and thought it read 12).

So does that leave me at potentially bad battery or ground?

I tried checking the quick test for the ground like you suggested and the car wouldn't start but I'm not sure if I hooked up the jumpers correctly (duh). I connected the - & + on the cobra and on my other car I hooked up the - and put the + jumper on the frame. If that was the right way, does that now point to a bad battery?

Thanks for your help, it's much appreciated!

sounds like a bad battery, sometimes they'll show 12 volts and have a bad cell, not enough amps though. bout anybody who sells batteries can check this also.

Sounds like a battery. Bad cell...
Pull it out - noting the "+" and "-" positions on the battery and which cable is which...
Take it to your local parts place and have them load test it.
It will probably fail...
If you purchase a new battery like an Optima style - be sure to slow charge it overnight after installation....
Good detective work...

BTW: The idea behind the jumper cable was to agument the existing ground on your car with the temporary jumper cable (negative battery to one side and chassis to the other)...If the car then started normally, your problem was the negative battery cable...Quite a few cars have had a loose or improperly crimped ground cables...It's a quick and cheap test.

Looks like I have to go back to detective school.

Before going to buy a battery, I decided to put the battery from my V6 mustang into the cobra just to make sure..... When I turned the key there was a 1-2 second hesitation, then the starter turned over slowly but the car started. I took it for a short drive, the dash guage read very low, got home, turned it off, then it wouldn't start again. When I turned the key there was a big hesitation like it was building up juice and then maybe a half turn by the starter and that's it. I put the multimeter on the (new) battery with the engine shut off and it was at 12.

(I had that same hesitation when you turn the key on with another car many moons ago and it turned out to be the starter. Something about not being able to bear the load or something.) The starter turned over like a champ with no hesitation when I gave it a boost earlier though.

I guess I need to start over. Any ideas?

Load test the battery anyway since it's out...
Let us know the results......
Longshot - Try giggling the ignition key when it won't start...
What's your car #?

How do I load test it? (It was a load getting it out of the trunk.)

Just take it to an autoparts place, they usually do it for free...

Thanks Blas. SPF 2162 by the way.

Your symtoms indicate a bad cell in the battery. The prescribed load test will verify it.

Rick,

While you might end up being right about a dead cell in my Optima battery, it doesn't explain why my Mustang battery will now not start the cobra after a test drive. hmmm

ZZmac:

You may find a direct short inside the battery. Try this....remove one cable from battery in your Cobra. Attach 1 jumper cable (note polarity!) to the removed cable and the other jumper cable to the post that still has the battery cable attached. Then attempt to start it.

Rick,

I put a perfectly good battery in the cobra from my other car and drove it around the block and now that battery won't start the car. So although there's a possibility that the original battery is defective, there still must be another problem, would you not agree?

When you say that "now the battery won't start the car", I assume you mean won't restart the Cobra, not the Mustang? Just like with the original battery in the Cobra...
*
OK...You have verified that:
The ground connection to the battery is good.
The ground connection to the chassis back by the battery is good.
The battery cable ends are all good.
The battery has been load tested and is at the proper level of charge.
Cable connections to solenoid on firewall are good.
Cable connections to starter are good.
Ground connections at starter & chassis are good.
When running, the charging system is working properly.
*
Next time the car won’t start,
I would try jumping around the starter solenoid on the firewall. Car won't start, just crank.
Use a remote start switch and jump across the 2 big cables on the firewall mounted starter solenoid. You can use a jumper cable but remember you have an aluminum firewall very close to those 2 terminals. If the car then cranks normally…you’ve isolated the problem to that solenoid or the ignition switch.

sounds like the alt. is not actually putting the charge into the battery and the car is running off the battery and draining it then will not restart.

after the cobra is started put a voltmeter on the battery terminals and verify at least 13 volts, or after starting remove one of the posts, there is a preferred one, don't remember, and see if the car still runs, should if it is not efi.

Battery battery and a damaged Alt regulator diodes
 

zzmac I have heard more than once about these optima batterys having internal shorts on 1 cell and killing the Alt diodes in the regulator. 13.5+ volts is not enough to running all your systems and and charge the battery. It sound like only 1 of the 3 legs in the alt is still working. Are you sure that the Alt belt is not slipping on the pulley? The belt is not glazed? You have no charging after your short road test. As far as trying to start the car with another battery, what is the voltage on that battery? 12.5 or high would mean you have a good battery but you could also have low CCA cold cranking amps. How many grounds are on the car? How many go from the frame of the car to the battery? Where is the battery located. I would remove, clean the mounting area to the grounds and reinstall. If you strip the contection, this will cause the same problem. With everything hooked up, can you twist the battery connections? If yes, this is a problem. If not, go to the batery cable other ends and test and clean them. Do you have under driven pulleys on the motor? If all checks out, Do the Pepboys or Autozone thing. May sure you go to 2 different places. I believe your battery shorted and cooked the Alt. Road test your car with your volt meter hooked to the battery and have someone hold it or tape it to the windshield for this test. If you see the voltage fall with the mustang battery, the Alt is cooked. Rick L.