Something funky is happening here. Your poor battery must be right on the ragged edge of having enough oomph to spin the starter properly. How long were you at the gas station, maybe 5 minutes? Any properly sized battery in semi-good condition (meaning the physical condition of the battery itself, plus the state of charge) should not be phased by running the heater fan for 5 minutes with the engine off. In your present scenario, it sounds like everything has to be uber perfect or the starter will bog, and that just isn't how it should be.

If you are planning to replace this battery, a good idea as the others have suggested, try a different brand. It could be this brand may be of poor overall quality. It's already been replaced once under warranty, right? If so, and the brand is fine but this particular batch was bad, most likely the replacement came from the same suspect batch. Same with the next replacement. Go to a different store and purchase a different brand completely. It's rare, but I have had several instances of new parts being bad. I've even had one instance where the replacement was bad, which was really hard to wrap my head around. That's why I strongly suggest getting a different brand. If hesitant to do that, do you have a known-good battery from another vehicle you can swap for troubleshooting?

Maybe one more thing to check before swapping out that suspect battery. More details on the AC ripple test in my next post. Excessive AC ripple (from a bad alternator) can cause all sorts of weird problems, so definitely rule that out. It will take all of two minutes.

 

How high? The general limit is 0.5VAC. That's half a volt, using the lowest ACV scale possible. Remember, set your meter to AC volts, NOT DC volts.

Here's a halfway decent video showing an AC ripple test, but I'll add a few caveats. Note this video actually shows a bad alternator pumping out excessive AC ripple. I found lots of other videos running the same test, but I linked this one because it shows a bad alternator, unlike the others:




The main gotcha in this video is the meter leads are on the battery, not the alternator itself. Actually, you can run the test like that first (at the battery) and see if it fails. If so, there's no need to put the meter leads directly on the alternator. The AC ripple will measure higher there, but it doesn't matter. You've already shown it's bad. No need to keep digging in that scenario.

So in practice, if AC ripple appears within limits at the battery, repeat the test with the leads directly on the alternator. As mentioned in previous posts, the location of the leads makes a difference. You wouldn't think a couple of feet of heavy cable would make any difference, but it can. I have observed this myself on multiple occasions. It's like tossing a stone into still water and watching the ripples dissipate the further they travel.

So for the most accurate results, put the meter's red lead on the big ouput lug on the back of the alternator. Put the meter's black lead on the alternator case. Run the engine at varying speeds and with both high and low electrical loads. As previously suggested, run the test with the alternator cold (right after the first start of the day, light electrical load) and hot (after a long drive with maximum electrical load).

Another quick and dirty method to check for AC ripple is to turn on the dome light and run the engine. See if the light flickers. It will probably be most apparent at low RPM and light electrical load, but try various combinations anyway.

Now for some Twilight Zone stuff, it's also possible a bad battery can cause excessive AC ripple. Among other duties, the battery also acts as a giant capacitor to smooth the (normal) small AC ripple put out by any good alternator. But if the capacitance action of the battery drops, a good alternator can put out excessive AC ripple. Normally a battery fails due to other age-related causes (leading to reduced storage capacity, etc.) before the capacitance shortfall is apparent, but not always. Read this interesting article for more details:


https://www.motor.com/magazine-summa...tery-of-tests/


Note how the author increased the total capacitance by adding a jump box in parallel to the suspect battery. This quickly smoothed out the AC ripple and brought it within specs, meaning the battery was bad. On a practical level, assuming you don't have an oscilloscope and jump box available, what can you do? Try swapping out the suspect battery with a known-good one, or a new one that is a different brand than what is presently installed.

As quick as the AC ripple test is, I'd highly suggest running that before trying any changes. Keep track of the test results before and after any new parts. That way you'd know if any changes had an effect.

 

Let's see, how long was I at the gas station, 5 minutes maybe? But my heater doesn't run with the key off engine off....

let me clarify, I shut the truck off with the heater fan on. 12.8 volts, I turn the key to "on" right before I depress clutch and crank over the engine and the heater fan kicks on for a split second, I immediately notice voltage drops to 12.2 volts, I reach down, turn off fan, and voltage goes back up....

so I'll swap my battery out tomorrow, cause that seems to be the census now. Any reason I couldn't drop down to a smaller cca flavor battery? This 1100cca variety was in the neighborhoods of $280.....

 

Okay, too much confusion going on here. Based on your previous description, I thought you had left the key in the ACC position, perhaps to keep listening to your ABBA tape. (I don't judge...) In ACC, the fan runs, so it all made sense.

To avoid any further misunderstandings, I see only one practical solution: Pick me up at the airport tomorrow. I'll catch the first flight in the morning. I'll be easy to spot, carrying all my electrical test equipment.

My needs are simple. A private room. Deviled eggs with lunch. And 4:00 to 4:30 is my Judge Judy time. No work will be performed then.

Until I get there, run that AC ripple test before trying anything else, as previously detailed. A failure there could explain a lot. You might even get lucky and not need a battery. So is the consensus a new battery? I'd say that's a good idea, but try the Hail Mary AC ripple test first. Absolutely free, and will take all of two minutes.

You mentioned getting a high AC ripple value earlier, but weren't sure you were doing the test correctly. The value? You may have already found the primary fault, but didn't realize it. And does the procedure given match what you did?

 

650 CCA should be more than enough that is about 800 CA I believe that was the size as delivered from the factory.

 

Well, I put the voltmeter in ac, lowest value was 200, and if I wasn't mistaken, it showed something like 35.something..... that's why I wasn't sure if I did it right. I'll double check tonight, but it was hooked up properly.

 

It had a 15 year old interstate battery in it when I got it that worked for quite some time, only thing I can get locally is duracrap and neverlast. And I've tried them all....

 

You got 35 volts AC? Not 0.35, but 35 whole volts? If that is true, never purchase that brand again nor even set foot in the store that allegedly tested that alternator. I'd suggest waiting in the parking lot at quitting time. When you see the clerk who operated the test machine, percuss upon him with a tube sock full of soap bars. Then flee at breakneck speed (I'd suggest leaving your truck running, since starting is still iffy). Drive to a distant city and purchase a reputable brand alternator.

 

There is not a NAPA near you? Their batteries are decent and most of them are made by either Interstate, Johnson Controls or Exide.

 

 

35 VAC ? WTF that would mean at least 2 Diodes have shorted. AC ripple was never really an issue in days past and we never tested for it as the Diodes used either worked or went open, they would not short and if they shorted they just failed completely in short order, they were designed to fail in that manner.

Really they must be using the cheapest lowest quality chinesium diodes they can find now a days.

Chances are the battery is damaged, it may come back but I would not count on it. Swap the Alternator

 

 

got in this morning to find out my voltmeter plug was still in and on, draining the battery all night. Showed voltage at 12.4 dang it!

I figure what the heck, I'll try to fire it up before I put it on the charger. Cranked over good as could be. Actually cranked while giving it gas for 10 seconds, even when voltage agent to 11 volts in the key off position, it spun over just fine, not a single instant of slow crank???? Voltage while cranking never went below 10 volts

eventually fired up and voltage is back charging at 14.18. Im lost now. I plan to spend all day figuring this out. I'll let it warm up, drive it shut it off, crank and crank and crank, this is entirely too crazy. It makes no sense.

 

The second picture is the correct setting. You want AC Volts. Holy crap, that's a bad alternator. Not just a little bad, but boat anchor category.

30V is well within the normal range of a 200V scale. The last thing I can suggest before replacing the alternator is to check the accuracy of the AC voltage reading. Shut off the engine so the alternator isn't turning. The AC volts should drop to zero. Then you can stick the meter leads (still set to ACV) into any wall socket in your house. The polarity doesn't matter. You should see right around 115VAC. If those two tests pass, you've confirmed your meter is good and therefore your alternator is kaput.

Back to your first picture, with the meter set to AC amps, you may have fried the meter's internal fuse. Not a big deal, it should be easily replaceable. I think it will only affect the amperage settings, not voltage.

 

I let it warm up, shut it off, left headlights and heater in the acc position for 30 seconds, voltage dropped to 11.4, cranked it over and it started up no problem.....next I'm gonna shut it off, let the battery draw down for a few minutes and try to crank again, it seems like I just can't get a slow crank this morning....