GeorgiaJeeper93 Posted January 31, 2017 Share Posted January 31, 2017 So I'm trying to find out why my truck keeps dying. I jumped it off, let the vehicles run for several minutes, took the jumper cables off, and it runs for about a minute, then dies. I also noticed its idling weird. it will idle high, then get really low, then sound like someone is tapping the gas pedal. It will die soon after that. The alternator is brand new, I tried 3 different batteries (can't find my multimeter at the moment to make sure they are good, they are all about 5 years old). So I think I have it narrowed down to the battery, or a connection to the alternator. In the morning I am going to find my multimeter, and recheck the alternator connections. Am I missing something else that it could be? Would a bad battery make it idle like that? Link to comment Share on other sites More sharing options...
Eagle Posted January 31, 2017 Share Posted January 31, 2017 If the alternator is working, it should run even with a dead battery. I suspect your new alternator was DOA. Link to comment Share on other sites More sharing options...
Hippie66 Posted January 31, 2017 Share Posted January 31, 2017 Possibly a bad connection. Check all grounds. Link to comment Share on other sites More sharing options...
GeorgiaJeeper93 Posted January 31, 2017 Author Share Posted January 31, 2017 If the alternator is working, it should run even with a dead battery. I suspect your new alternator was DOA. Is that true even if the battery was drained to the point where it won't hold a charge? Link to comment Share on other sites More sharing options...
Knucklehead97 Posted January 31, 2017 Share Posted January 31, 2017 If the alternator is working, it should run even with a dead battery. I suspect your new alternator was DOA. Is that true even if the battery was drained to the point where it won't hold a charge? one time I jumped my brothers old XJ off, drove it to the auto parts store, and left it running while they tried to charge the battery for me. Disconnected the battery while the engine was running and it kept on truckin without a battery for over an hour Link to comment Share on other sites More sharing options...
madog7200 Posted January 31, 2017 Share Posted January 31, 2017 If the alternator is working, it should run even with a dead battery. I suspect your new alternator was DOA.Is that true even if the battery was drained to the point where it won't hold a charge? one time I jumped my brothers old XJ off, drove it to the auto parts store, and left it running while they tried to charge the battery for me. Disconnected the battery while the engine was running and it kept on truckin without a battery for over an hourHow on earth is this possible? Diesel is tho only thing I can come up with Sent from my SM-G930P using Tapatalk Link to comment Share on other sites More sharing options...
DirtyComanche Posted January 31, 2017 Share Posted January 31, 2017 A renix will run without a battery providing the alternator is good. Won't comment on a HO. You've got issues and without a multimeter there is nothing to tell you beyond checking all connections for tightness and lack of corrosion or contamination. Link to comment Share on other sites More sharing options...
HOrnbrod Posted January 31, 2017 Share Posted January 31, 2017 While doing your multiple battery cable connections using jumper cables, did you ever get the + and - cables crossed and cause a direct short aw-sheite arc? Link to comment Share on other sites More sharing options...
Knucklehead97 Posted January 31, 2017 Share Posted January 31, 2017 If the alternator is working, it should run even with a dead battery. I suspect your new alternator was DOA.Is that true even if the battery was drained to the point where it won't hold a charge? one time I jumped my brothers old XJ off, drove it to the auto parts store, and left it running while they tried to charge the battery for me. Disconnected the battery while the engine was running and it kept on truckin without a battery for over an hourHow on earth is this possible? Diesel is tho only thing I can come up with Sent from my SM-G930P using Tapatalk it was a 97 XJ with an OBD2 HO. Not diesel at all haha. Link to comment Share on other sites More sharing options...
GeorgiaJeeper93 Posted January 31, 2017 Author Share Posted January 31, 2017 While doing your multiple battery cable connections using jumper cables, did you ever get the + and - cables crossed and cause a direct short aw-sheite arc? Nope. I'm always careful with anything electrical. Link to comment Share on other sites More sharing options...
DirtyComanche Posted January 31, 2017 Share Posted January 31, 2017 Check the fusible link between the alternator and the ignition relay. Link to comment Share on other sites More sharing options...
shelbyluvv Posted January 31, 2017 Share Posted January 31, 2017 Something with the alternator is not right. Either wiring, fusible link or the alt itself is dead. It should and will run without an alternator. Link to comment Share on other sites More sharing options...
Pete M Posted January 31, 2017 Share Posted January 31, 2017 yup, most any vehicle will run purely on the alternator. now, if it has a completely dead battery still installed, that's a whole 'nother issue. for example we were having an heck of a time getting my buddy's bronco to keep running and it turned out the battery had died mid-drive. once we separated it and got it jumped, we drove on the rest of the way home no problemo. :D Link to comment Share on other sites More sharing options...
Tactical Bacon Posted February 1, 2017 Share Posted February 1, 2017 Something is stopping the alternator from charging the vehicle. I'd suggest bench testing the alternator to make sure it's putting out voltage then go from there on checking whether you have a loose wire. You can also turn the key to the on position and see if you have voltage from the signal wire if you find your multimeter, normally 12V. Link to comment Share on other sites More sharing options...
GeorgiaJeeper93 Posted February 1, 2017 Author Share Posted February 1, 2017 Picked up a new multimeter. Two of the 3 batteries read 0.0, and the third, read 8.4. So tomorrow I will be swapping in the battery that read 8.4, jump it off again, see if the alternator will charge it up. If not, then I will take the alternator back out and get it tested. Link to comment Share on other sites More sharing options...
GeorgiaJeeper93 Posted February 1, 2017 Author Share Posted February 1, 2017 excitement got the best of me. I went out and swapped the batteries just now. Jumped it off, let it charge for about 10 minutes, took the cables off, and it continued to run for a good 15 minutes. When it finally died the battery read 11.60. Which is an improvement, because when I took off the jumper cables, it read 10.3. So I'm still not sure what the culprit is. I would think if it were the alternator, it wouldn't have charge at all on its own, correct? Link to comment Share on other sites More sharing options...
johnj92131 Posted February 1, 2017 Share Posted February 1, 2017 A properly function alternator should be putting out close to 14 volts DC at the battery with the engine running. Did you measure the charging voltage with the engine running? Your fully charged battery should measure 12.50 volts at least with no load. That was the spec we used years ago to ship new batteries to the car factories when I worked a Gould Automotive Battery decades ago. Link to comment Share on other sites More sharing options...
shaylec Posted February 1, 2017 Share Posted February 1, 2017 When the engine is running, if you disconnect a battery cable from a battery terminal, the engine will continue to run if the alternator is good. If the engine immediayely dies after the cable is removed, your alternator is dead. Link to comment Share on other sites More sharing options...
shaylec Posted February 1, 2017 Share Posted February 1, 2017 I have heard that removing the battery cable while the engine is running could be hard on the rectifier diodes in the alternator. But i have never experienced this personally. I just wouldnt make a habit of doing this. Only do it once when diagnosing your engine stalling problem. Link to comment Share on other sites More sharing options...
yxmj Posted February 1, 2017 Share Posted February 1, 2017 Since you have a muti-meter try this easy test.....with the battery in and connected and the truck running take a voltage reading across the battery terminals....what is the voltage? It should be somewhere between 12.7 and 14.7 volts.....is that what you get? And this may be off topic but I recently got one of these... http://www.catautopower.com/25-amp-battery-charger.html This is cat brand but there are other brands out there.....not only will it charge your battery....but it has an engine start feature (boost) that works (Winnipeg -40 trust me) but it also has simple push button features that allow you to 1) check battery voltage.....2)do an in vehicle alternator check....3)and recondition the battery. and you don't have to guess if the battery is fubar....if it is it tells you right on the screen. . :MJ 1: . Link to comment Share on other sites More sharing options...
Gene Posted February 1, 2017 Share Posted February 1, 2017 Hi GeorgiaJeeper, Electrical problems can get confusing. Consider some basics: 1. For a vehicle to run, it generally needs at least 9 or 10 V available. This can come from a battery, or from an alternator. A vehicle can run on battery power alone, with the defective alternator. A vehicle can run on alternator alone, with the battery removed. 2. However, if the battery is very very low, it can "suck up" all of the alternators output, especially if the alternator is weak. 3. Do you have, or can you get a battery charger? Charge up the better of your batteries, if the charger output is relatively low output, this may take several days. After the battery is fully charged, disconnect the charger, let it sit for an hour, and then check voltage at the battery. A good battery will have about 12.8 V. 4. You can't really depend on the alternator to charge a fully discharged battery. It would take several hours, at least, of engine running above idle to fully charge a totally discharged battery. 5. As stated in another post, with a fully charged, good battery, a good alternator will typically raise the system voltage to around 14.4 V. It doesn't have to be exactly this. The voltage will be lower at idle, and may increase if you rev the engine. The voltage will be lower with a significant electrical load, such as headlights being on. Why don't you try the above, especially with the fully charged battery, and see how things check out? My guess is that ALL the batteries are very bad, and "eating up" all of the alternator output. Good luck! Gene Link to comment Share on other sites More sharing options...
Knucklehead97 Posted February 1, 2017 Share Posted February 1, 2017 If you're a speedperks member at Advance Auto then you can get at least 40$ off a battery if you buy online and pickup in store. I paid exactly 100$ for a new group 34 battery after taxes Link to comment Share on other sites More sharing options...
johnj92131 Posted February 1, 2017 Share Posted February 1, 2017 Try Costco for a group 34 battery at $83 plus tax. Link to comment Share on other sites More sharing options...
shaylec Posted February 1, 2017 Share Posted February 1, 2017 Thanks for the link. I really like that little charger's test features. Not expensive either. I admit, i use the pull the battery technique when i don't have a meter on me, and I'm always worried about damaging the alternator when doing it. Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 1, 2017 Share Posted February 1, 2017 Me too. yxnj, have you tested all the features it claims to have? Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now