Automotive opinions so I’m of the opinion this belongs here.
1994 Suburban 1500 (gas). Get in the truck and the ignition is totally dead. Not even the classic light the instruments but won’t crank scenario of a low battery but dead to the world.
Fetch the battery pack, the truck starts okay and runs for 15 seconds until the battery pack auto-disconnects, then it’s back to totally dead.
Maybe the battery is shorted or something, keeping the alternator from alternating. Disconnect the truck battery, start the truck, same story: Totally dead after the pack disconnects.
I have been in situations where the bridge rectifier on an alternator was kaput. The auto ran fine for a couple days off of the battery until one night he was out after dark and the headlights pulled the battery down after about forty-five minutes. We wound up walking home.
So, if the battery is dead why won’t the alternator put out? If the alternator is dead, what killed the battery? Is it a murder-suicide pact?
The battery is still under warranty so I’d rather drive down with it to Pep-boys and get it replaced, but not if it won’t do any good. Opinions?
Dead battery and dead alternator. Possibly just the diodes or a disconnected wire running to or from the alternator or a short as you mentioned having the same effect.The battery may take a charge again but must be at least drained now.
How long had the vehicle sat unused before you discovered this? If long enough I’d suspect you’d had an alternator failure and were running on the battery last time you used it. Then time and phantom loads drained the battery stone dead while it sat.
A truly hard-drained lead-acid battery will be permanently damaged. It might well take a charge and work fine in a vehicle w a good alternator. But it’ll have a drastically reduced life and also reduced max CCA. Which might be an issue depending on what winter is like were you live.
At which point your best bang for buck move might be to replace the battery under warrantee now while it’s still fairly new and you’ll get a large credit towards the next one rather than waiting 12 or 18 months & get a smaller credit when it finally dies prematurely.
A common way to test generators (back in the day when cars had DC generators and not alternators) was to disconnect the battery and see if the car continued to run. If it did, then the generator was probably OK. If it didn’t, then the generator was probably toast.
A lot of people (especially old-time mechanics) think that’s still a good test, but it’s a very dangerous thing to do on a modern vehicle. The alternator puts out alternating current, not a constant DC voltage, so it’s nowhere near a constant DC. Modern cars rely on the battery for a lot of the bulk filtering and voltage regulation. Without the battery to smooth things out, the output of the alternator van vary wildly. That’s not so bad on a 1970s era car with a very simple electronic system, but a modern car with its many computers and what-not can be easily damaged.
It’s probably not quite as dangerous on a mid-90s Suburban than it is on a 2020+ vehicle, but still, it’s a bad thing to do. Don’t do it.
Check the battery with a voltmeter. A fully charged lead-acid battery is about 12.6 volts. If it gets too far down below 12 volts the battery tends to chemically self destruct.
Since the battery is still under warrantee, I would have it checked out and replaced if necessary.
Once you have a good battery, measure the voltage with the Suburban turned off (should be somewhere around 12.3 to 12.6 volts depending on how fully charged it is), then start the Suburban and measure the voltage again. If it doesn’t go up to somewhere around 13 to 14 volts, the alternator is toast. Note that this test doesn’t necessarily work so well on a modern car with a smart charging system. But for a mid-90s vehicle it’s a quick and easy test to see if the alternator is charging the battery or not.
If it doesn’t start with a good battery, you have some other issue (bad ground, bad wire, bad starter, bad relay if it has a relay, etc).
The closest thing to a computer is the fuel injector and the spark module but thanks for the warning. The current daily driver is a Bolt EV and when the 12v battery in that goes wonky it can play hob with the car’s power-up routine. Recommendation there was to carry a 10mm wrench to disconnect the battery for a hard reset so you can hopefully get to the battery store after reconnecting it.
It’s up in Flagstaff and the Mogollon Rim. Not so much in Mesa. Real rare here in Miami too. Good thing.
I now realize I’d gotten you partly connected to @Gatopescado who IIRC lives in the wilds of Wyoming and also has a motley collection of vintage vehicles. He gets winter there I hear.
I thought cars of that era were still OBD-1, and still had a lot of the modern suite of sensors, etc. I mean, you’re still going to have O2 sensors, throttle position, MAF/MAP or some other way to determine the amount of air entering the engine, and all the other stuff to properly run a fuel injected engine.
But yeah, it sounds like if you start it with the battery pack, and it runs fine until the battery pack shuts off, that it’s something to do with supplying current to the engine. It’s hard to say if it’s a bad battery or alternator without more information; I concur with @engineer_comp_geek’s advice to get the battery checked/replaced and work from there.
Battery 0v so it is in doornail mode. Neg post to frame 0-ohms so that is good. Waiting for Tuesday before running around more.
Yeah, we have to import it here to Mesa.
Driving around town in the Bolt EV this winter, with the temp at 40-degrees or better, I was hard-pressed to get above 3.6 kWh per mile. I suddenly understood why the folks in Minneapolis were complaining.
In contrast, in the summer with our 105+ temps I was easily able to get 4.2kWh and at times exceeded 4.5. Shows the efficiency difference between heat pump and resistive heating.
That’s not just dead, that’s rather impressively dead.
I suspect that the alternator went out first and then, without a working alternator to charge it, the regular load on the truck killed the battery. But, you won’t be sure until you get a good battery in there and test it.
As expected, alternator and battery both. Not expected, the battery was two months past warranty – this fallible memory of mine slipped a digit on the year bought.
