Alternator or battery???

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spacewelder

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So I've been having this problem where my car won't start. Background: 74 Swinger, 390 stroker, MSD 6AL IGNITION, new mini starter and new 70 amp alternator. Battery doesn't seem to like to hold a charge. And when it doesn't have a full charge it won't even turn over. Power is getting to the MSD and also to the starter relay. When key is in ON position the gauge shows just negative. It also is starting very slow. It does spark when I have full battery. When I drive and play the stereo, it shows charging but will fail to start again or crank very slowly if I stop into the store. Any ideas?
 
What size battery are you using? You may need one with more cranking amps. Also make sure your grounds are good. If you don't have the meters, Autozone will test your battery and charging system for free.
 
800 Cold cranking amps on the Battery. All grounds are good from what I have checked. And I may have to do that
 
Just because the label SAYS that does not mean "it is." It could be bragging, or it could be defective.

Procedure...........Charge the battery

Look of "leaks" that is leakage current when parked.

Pull battery and have it load tested.

Use same (load) tester to obtain starter current draw

As always, clean clean clean connections, and replace any suspect cables.

Last measure running battery voltage. Warm, with battery "normal" charged, voltage should run 13.8--14.2, in no case below 13.5 above an idle and in no case above 14.5
 
Remove the stereo , my dart hasn't had one since 1982.

I enjoy listening to the engine
 
67Dart273 said:
Just because the label SAYS that does not mean "it is." It could be bragging, or it could be defective.

Procedure...........Charge the battery

Look of "leaks" that is leakage current when parked.

Pull battery and have it load tested.

Use same (load) tester to obtain starter current draw

As always, clean clean clean connections, and replace any suspect cables.

Last measure running battery voltage. Warm, with battery "normal" charged, voltage should run 13.8--14.2, in no case below 13.5 above an idle and in no case above 14.5
Click to expand...

Just ran it for a good couple minutes and read the battery voltage with all electronics off and it was only reading 12.2 volts. I think it's time for a bigger alternator
 
Stop by Autozone and they will test the battery for free. Put it on a charger first. You can buy simple 10A chargers for $20 that will charge overnight. That will help separate the alternator from the "is battery good?" question.
 
If you don't run it at FAST idle, the charging system is running too slow to put much charge into the battery. So the test you ran is not an adequate test by any means; you have not proven/tested anything new yet; you know what you knew before.... that something is not right.

Follow the instructions given to get usable test results:
- Clean the terminals and all heavy wire connections everywhere very thoroughly, and the voltage regulator connection to chassis
- Charge the battery overnight; then remove the charger and let the battery 'rest' unconnected for a couple of hours to dissipate the surface charge and then measure the battery voltage. If it is charged and holding, it should read 12.6-12.7 volts.
- Load test the battery at some point in time to be complete; you have a heavy engine cranking load to support
- After the battery is properly charged, then run the car 'til is is warm and at FAST idle, check the voltage across the battery and see if it falls in the range of 13.7-14.3. If so, then you are good on the battery and charging system. If not, THEN it is time to look at the charging system further.

Or, throw parts at it if that is your preference. Some folks like that; OK by me..... but, again, you don't have any usable test results yet. Ultimately, it may be the charging system but you don't know what part, or if there are other underlying problems that will prevent ANY alternator from working right (like bad grounds or other connections...)
 
To continue last post.........

Make sure you run it fast enough. Make sure battery is not severely discharged. If warm running voltage is again "that low" (well below 13.5) then make these checks...........

Assuming? you have the factory Mopar type setup?

Turn key to run, engine off. Unhook the GREEN field wire at the alternator. You should see a small spark in subdued lighting. Take a clip lead and ground that alternator terminal. Not the wire, the alternator field

Now start and run the car, monitoring battery voltage. Slowly bring up RPM. It should easily pass 14, try to keep it below 16. IF NOT............

Move your voltmeter to the alternator output stud. Recheck. If voltage remains quite low, it is not charging. If the voltage at the stud is quite high, way over 16, you have an open connection between the battery and the alternator output stud.

If voltage at the output stud is low, take a second clip lead, hook to a battery source such as the starter relay big stud. DO NOT use the alternator stud. Unhook the second field wire, the blue, and hook the other end of the clip lead there. So..........

You have one clip lead from battery to one field

You still have the second clip lead grounding the second field terminal.

Repeat the run test. if output is still low in voltage, something is wrong in the alternator.

============================

IF the voltage "came up" in the first run test, but will not charge up to voltage when hooked up "normal," This might be in the field circuit.

Hook everything up "normal." Turn key to run, engine stopped. Measure voltage at the blue field terminal WITH the wires all hooked up. Should get close to battery

Take your clip lead, unhook the BLUE field wire, and ground that alternator field terminal

Unhook the VR connector. Inspect for corrosion. Work in and out feel for "tight." Next, devise a way to jumper across the two connector terminals. Monitor battery voltage and once again run the engine "up." IF it charges and voltage rises up above 14, .......then........

REMOUNT the VR making sure you scrap the VR and firewall clean and use star lock washers. Wiggle the connector. Re--test

If it still won't charge hooked up normal, replace the VR. Buy a good one.
 
WHY are you doing all this?

Because with only a test lamp, clip leads, and a meter, you can test the entire system right on the car, and if done right, you will KNOW what the trouble IS

The reason these tests are as written is because you need to eliminate different "sections" of the problem

Is it a bad connection in the charge wire?

Is it a bad alternator?

Is it getting field current from the blue?

Is the VR wiring OK?

Is the VR grounded?

Is the VR bad?

ABOUT those parts store "testers?"

RARELY is a tester able to tell if a component is "good"

ONLY if the tester is "a correct tester," is set up correctly, is operated correctly, AND BY an honest person, it will tell you "if it's bad"

Very few if any parts store testers can fully load test a "big" alternator. It takes a BIG electric motor to "pull" a 100A alternator to full output. I built a tester once, we had an unused 15 hp 3 phase motor. Some of the big truck units would dog it down some
 
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