I have a 1996 Dogde Ram Van 2500. Thursday night, I went out for a burger, driving maybe 5-7 miles. I sat in the parking lot and ate and used the dome light to read for a few minutes (something I have done a lot with no problems). When I went to start the engine the battery was almost dead. I gave it a rest for a few minutes, and was able to turn it over, but it wanted to stall. I drove home nursing the throttle at stop lights so the motor wouldn’t die. Sure enough, when I got home and let off the gas it died immediately and didn’t want to crank. The next day, I go out and it starts immediately with a lot of power. I remove the negative terminal on the battery and the engine does not die, I couldn’t remove the + terminal because I didn’t have the tool for it.
At first I’m thinking it is the alternator because the battery seems to be good, but removing the battery lead should make the engine die if the alternator isn’t cranking out juice, no? So what say ya’ll?
Don’t do that, it’s not good for either the alternator or the regulator which expect the load of the battery to be present, and require it for proper operation. At one time, when cars were electrically unsophisticated, this was an effective quick and dirty test for the alternator. Nowadays, it’s strongly discouraged.
That said, in this case I rather suspect the battery. How old is it? If you have a voltmeter, measure athe voltage across the terminals the next time it acts up like this. If it’s significantly lower than 12 V, it’s probably time to replace it. If it’s below about 10 V, it’s definitely on its last legs.
Goodness. I only did if for a second or two. I hope I didn’t fry anything. Yes the battery is several years old. But why would it be charged the next day. Believe me, I hope it IS the battery. That’s a ten minute DIY job. The alternator is a knuckle buster to change and I am getting too old for that kind of pastime so off to the mechanic if that’s what is up.
Not a mechanic, but could it be a fuel delivery problem? Sounds like it could be, maybe.
I’ve had numerous batteries & alternators go out, and don’t recall those exact symptoms. If I’m off base I am sure someone will point it out.
Can’t both batteries and alternators be bench tested?
I’d say the battery probably has a dead cell or two. It’ll charge enough to start the engine, but won’t take a prolonged discharge, like the dome light and it’s slow to recharge. If the batt. is 3-4 years old, especially in a cold climate, it’s time for a new one. Most batt. shops can run a load test before you buy and if there’s another problem they should tell you.
(bolding mine)
This has never been an approved test for an alternator. Back in the days of DC generators you could run the engine with no battery and no damage. As you stated it is very hard on the alternator diodes, and regulator. You can also kill any onboard electronics this way. Think radio, any of the many electronic control units. This could be a very expensive mistake.
Never disconnect a battery while the car is running.
You have the voltages all screwed up
All of the following assume no surface charge. Surface charge is a phantom voltage that exists above the batteries actual state of charge. It will show up for 1-4 hours after a battery has been charging either from an alternator or battery charger. To remove a surface charge either wait or turn on the headlights for 30-40 seconds. Then measure the voltage with the key and all electrical items in the car off (Disconnecting one battery cable would be a real good idea, because then for sure you will get an accurate reading)
Anyway:
12.6 V and above = Fully charged battery
12.45V = 3/4 charge
12.20 V = 1/2 charge
12.00 V = 1/4 charge
Below 12 V = dead.
Now these voltages do not tell you if the battery is good, only if it is charged or not. You can put a brand new top of the line battery in a car and if the alternator is not charging it will go to below 12 V is a very short time. This does not mean that your battery is bad, but it does mean that it is discharged.
A slightly better test is to check the voltage with the engine running. With the engine running, all electrical accessories off and at about 2000 RPM you should see a voltage a of between 13.5 and 15V at the battery.
These are not definitive tests only general indicators.
You will need specialized test equipment for a definitive diagnosis. Most auto parts stores and places like Sears automotive will test your battery or battery and electrical system for free, (they are trying to sell you a battery) Sears in particular does a very complete and comprehensive test. I have taken cars in where I have already diagnosised a bad battery and watched them verify my diagnosis. A very complete job I must say.
You might want to consider going to a place like Sears and having your system checked out. It used to be free with when you bought a battery. You might want to check.
Now if I was going to bet, I would bet on a attery. Lots more batteries go bad then alternators do, but without a proper diagnosis, I can’t be sure.
I see I wasn’t entirely clear. I was telling him to check the voltage with the car running with a normal electrical load when the symptoms appear, not the no-load voltage. As you say, there’s should be around 13 V, give or take, when everything’s running normally. I agree none of this is definitive, so strike the “definitely” from the previous post. I also made the (possibly unwarranted) assumption that the alternator was good, which it seemed to be based on the OP’s description. That better?
Better, but any voltage below about 13.5 under the engine running conditions that I described above indicates a bad alternator / regulator / or wiring issue, not a necessarily a bad battery. But if you had a dead battery it might show up as a low voltage with the engine running. This is why all the fault tracing charts for electrical systems start with checking the battery first. The problem here is you have to have a known good battery before you can fully diagnosis the rest of the electrical system.
Doesn’t crank and runs poorly one night, next morning cranks and runs normally without doing anything to charge the battery = bad battery or bad electrical connection. The alternator may or may not work normally, but a bad alternator wouldn’t give that set of behaviors.
My first guess is a bad cell in the battery, as mentioned above. This may or may not show up under electrical testing of the battery. It will show up in a hydrometer test, which is possible on servicable batteries (w/ removable vent caps) but not possible with sealed batteries.
Whether or not you replace the battery, it makes sense to check, clean, and tighten (as necessary) all battery cable connections, i.e. both ends of both cables.
Negatory, terminals were fine. I wish I had my meter with me I am going to do the Sears thing, if there is one I can make it to, or I am sure Pep Boys can do the same deal. Thanks a lot for the advice.
I am going to do the Sears thing, if there is one I can make it to, or I am sure Pep Boys can do the same deal. Thanks a lot for the advice.