You made my hair stand up on end. Never, never, ever remove a battery cable while the engine is running. That is a real easy way to destroy all the computers on your car. This is a trick done a long time ago by mechanics who didn't understand how these simple systems work. Today a professional caught pulling this stunt will immediately be fired.
If you're really interested later, I can explain why this is so, but what happens when you remove the cable tells you nothing of value. The engine can stall with a perfectly good generator, and one that is defective can keep an engine running.
The place to start is by checking this article:
https://www.2carpros.com/articles/how-to-check-a-car-alternator
Be aware they're using a high-end voltmeter with the "auto-ranging" feature. That's an option you don't need. You can find a perfectly fine meter for $7.00 from Harbor Freight Tools. Similar models can be found at Walmart or any hardware store. I can help you set it up if you need help.
The first step is to measure the battery's voltage with the engine off. If the battery is good and fully-charged, it will read very close to 12.6 volts. If you find it's closer to 12.2 volts, it's good, but fully-discharged. It should be charged at a slow rate for a couple of hours with a small portable charger. Should it be down to around 11 volts or less, it has a shorted cell and must be replaced.
Next, measure the voltage again with the engine running. Now it must be between 13.75 and 14.75 volts. If it is, that only means it is okay to perform the rest of the tests, but that requires a professional load tester. Only pursue that when you're having a problem. Those will include a "full-load output current" test, and a "ripple" voltage test. There are a few testers capable of making a printout of the results. Those display ripple voltage as an actual value, but the more common testers simply show it as "low" or "high" with a series of LED lights. High ripple voltage is usually found when the generator is only able to develop exactly one-third of what it is rated at. That's where it can keep an engine running, while it can't develop enough current to meet the demands of the entire electrical system and keep the battery charged. The battery has to make up the difference as it slowly discharges over days or weeks.
Starter symptoms can confuse this issue even more. All motors draw really high current to get up and running, then that current drops down to keep it running. When the battery is partially discharged or weak, it can't supply the higher current. The starter will run too slowly, and it may appear to drag, even though there's nothing wrong with it. This test is a little tougher, but the part you can do is to measure the battery's voltage while a helper is cranking the engine. It should not drop below 9.6 volts. That's the industry standard. To be accurate, the engine has to be disabled to prevent starting, then this test is run for 15 seconds. Typically you're going to find that voltage is a good two volts higher, or a lot lower. If you find it's lower than 9.6 volts, we can figure out if it's due to too much current being drawn by the starter, or if the battery is too weak or discharged to supply the needed current, with the professional tester.
You might consider having these professional tests performed before you buy a new starter. Way too often people assume the starter is bad, they replace it, then they come here when the new part didn't solve the problem. If the starter really is dragging as you suspect, jumping the battery from another car isn't going to change anything. It's still going to crank too slowly.
Mar 11, 2024 at 11:13 PM
