I Guess I Need a New Alternator -- My Fault?

I have a 1997 with about 120k miles.

First ---- The other day, my wife and I were in stop-n-go traffic and it died --- right out the blue. It has never done this before. Second, about two times in the past week --- it cranked very poorly, but has generally started on the second try. Most of the time, however, it has done fine. Again, we have not had these problems in a long time. Third, we had starting problems about 1 year ago. I cleaned the battery terminals, which were very corroded, and everything was back to normal --- until recently.

Given that evidence, I opened the hood to take a look at the battery cables and saw very corroded terminals. I have some pics, but I don't know how to upload them.

I took the battery completely out, and cleaned everything as well as I could. I put it all back together and could not start it. I jumped it --- let it run --- but it would not start again after shutting it off.

I took it to O'Reilly Automotive. They could not check the battery because I could not turn off the Jeep, but they checked the alternator and told me it was bad. I don't have a clue about the test they used.

Now --- it is as dead as a doornail in my driveway.

I have a few of questions.

Do these symptoms sound like alternator failure?

Did I ruin the alternator by using water to hose out the battery tray? I tried not to get it very wet, but some water did get on it.

Does everyone's Jeep batteries corrode like crazy? If not, what is wrong with mine? I wish I knew how to post pics. The corrosion was awful.

Why did it stop running after I took everything apart and put it back together? What did I do wrong? I felt like I was being responsible and proactive, but now I feel like I should have left well enough alone.

A long time ago, I had alternator problems in an old car that I had. I removed the alternator and changed the bushings inside the alternator. Is that an option with my 97 XJ? I mentioned it at O-Reilly and they looked puzzled.

Final question --- O'Reilly wants about $120 for an alternator and a $70 core charge. Is that reasonable?

Sorry for the long post. I am going to spend my evening searching for posts on alternator replacement.

Thanks in advance for insight. Take care.

Let's see:

You almost certainly did not harm the alternator by hosing out the battery tray.

It might have died after you took it apart because of hard oxidation on the terminals or the battery posts. You need to get out something like a knife or an actual battery post cleaner and get down to shiny lead.

I would not spring for a new alternator until the battery situation is cleared up. You could have a bad battery, a bad alternator, or both. I would first make sure you have a battery that can take a charge, and is charged, and with clean terminals. Test the voltage at the battery before starting. It should be something around 12.5. Now start the engine. Voltage should now be something in the vicinity of 14. If it's still down around 12, your alternator is not charging, and after confirming that the wiring is not at fault, you will probably be looking at a replacement.

If your alternator is going bad because of worn brushes or dirty slip rings, you ought to be able to fix it, but I don't know who has the parts these days. It might take some hunting. I've done a number of alternator repairs of this sort, but never a Jeep, so I don't know whether the brushes can be easily found or whether they require soldering in. Worn brushes will often work intermittently. If you run the engine, and the alternator fails the test, try hitting it with a long stick or something (be careful of the fan and belt and stuff!). If it wakes up, that's a pretty good sign of worn brushes.

Not all batteries corrode, but some do. Wash things up with baking soda, and make sure that there isn't a bunch of corrosion under the rubber coating of the battery holddown. Liberally smear the battery posts and terminals with vaseline before reassembling, and daub more vaseline on the terminals after.

The easiest wat to check if your alt. is bad is to disconnect the battery while your jeap is running. If it dies you need yourself a new alt. As far as a little water running your alt. no it won't hurt it...mine gets wet every time it rains.

MogifiedXJ said:

The easiest wat to check if your alt. is bad is to disconnect the battery while your jeap is running. If it dies you need yourself a new alt. As far as a little water running your alt. no it won't hurt it...mine gets wet every time it rains.

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Correct, but not a good idea on late models. It can cause voltage/current surges, which can kill your computers...

I do it a bit differently - just check your battery voltage with the key OFF, and again with the engine RUNNING. If it's not higher when the engine is running, you're running off of your battery, and need to give your alternator a seeing-to...

5-90

If your battery terminals keep corroding the battery is leaking at the post clean every thing and get a new battery first.

5-90 said:

Correct, but not a good idea on late models. It can cause voltage/current surges, which can kill your computers...

I do it a bit differently - just check your battery voltage with the key OFF, and again with the engine RUNNING. If it's not higher when the engine is running, you're running off of your battery, and need to give your alternator a seeing-to...

5-90

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Sorry about that I didn't mean to give advice that could screw someone's jeep up. However, I've got a renix jeep and it's never messed with it. The obd I & II it might though like you said...

MogifiedXJ said:

Sorry about that I didn't mean to give advice that could screw someone's jeep up. However, I've got a renix jeep and it's never messed with it. The obd I & II it might though like you said...

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No problem - you may now consider yourself edified... RENIX is pretty sturdy - I've only known of three RENIX ECU's to fail worldwide (I was too late to catch the first one, the second one is here - came from Durbanville, South Africa - and the third should be on the way sooner or later. I'm in no hurry. All three seemed to suffer from blown injector drivers.)

ChryCo isn't going to be as hardy as RENIX, and don't even get me started on Ford TFI-IV. However, solid state electronics can be quite picky...

Nominal battery voltage should be 12.6VDC, and nominal alternator voltage will run from 13.5VDC to 14.5VDC or so (not too much higher!) and should definitely be higher than battery voltage...

5-90

Thanks for all the feedback everyone.

Here is my plan ---- based on what you have all said.

First a new battery and spend a little more time cleaning the cables. I cleaned them well, but I will work some more on it. Then I will investigate further into the alternator problem.

Is the amount of corrossion on my battery the result of me buying the cheapo Everstart at Wal-Mart? I guess I will go for a step up tomorrow. There is a small place in town that sells only car batteries. I guess I will go there.

I always thought that a sign of alternator failure was the lights dimming and getting brighter in concert with engine RPM's. I guess this is no longer the case?

I lay you odds the "stall" was the battery connection coming apart (due to corrosion) which sent the alt into max output mode till it self destructed (luckily, it didn't take the computer with it!)
I see cars every day (commonly Hondas and Mazdas) with the electronic ignition dist blown due to these power spikes.
If a car over powers, then too much power can make things pop, BUT if you run the battery low, then the computer can die from overheating because it tries to draw as much power as normal (R = AxV, IIRC) and in so doing, draws more amps to make up for the lack of voltage, so resistance goes up and more internal heat is made. At least that is what I remember I was taught in Aircraft Technical Systems at CFB Penhold, Alberta in the summer of 1975 when I was but a young Flight Sargeant in charge of a bunch of new recruits and teaching mechanicals while learning electrics, hydraulics and newfangled electronics)

5-90 said:

ChryCo isn't going to be as hardy as RENIX, and don't even get me started on Ford TFI-IV. However, solid state electronics can be quite picky...
5-90

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I've personally seen a Ford EEC-IV computer fried by disconnecting the battery. This was a custom SAE formula car with a motorcycle engine and Ford fuel injection. The engine guy wired in the required battey kill switch and tested it out with the engine running the night before we were supposed to race and fried our only computer.

Inside the EEC-IV uses a single zener diode to control the voltage and it can't handle prolonged large voltage spikes. Once it fries from the spikes, you're sending those 40-volt spikes through the electronics. The damage was too extensive to repair (and I've fixed a lot of EEC-IVs with blown output transistors). The next wiring iteration had the alternator feed on the battery side of the cutoff switch.

langer1 said:

If your battery terminals keep corroding the battery is leaking at the post clean every thing and get a new battery first.

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You may even want to consider replacing the cables too. Difficult to see if the corrosion traveled down the cable under the insulation.

Again, thanks to all who posted.

In the end ---- I changed the battery and the problem seems to be solved. The alternator seems to be OK --- so, I feel relieved.

I am angry at Wal-Mart, but I still put one of their batteries in it. The reason is that I took my old Wal-Mart battery in to have it tested. It tested good. I didn't believe it and took it to O'Reilly. It tested bad. I took it back to Wal-Mart and it tested good again. However, the guy said he would adjust it for me anyway --- a little less than $20 on the adjustment. Had he not adjusted it, I would not put another Wal-Mart Neverstart in the Jeep.

Another issue --- the corrosion has ruined my battery hold done bracket. I am going to buy a new one or fabricate one. I will search the posts, but any feedback is appreciated.

forgive me if im wrong, but the battery is part of the electrical circuit with the alternator, right? so why would removing it show a problem? if u pull that part (or any part) of the circuit out, wouldnt the circuit be broken no matter what? we had a battery in my work truck go bad...it still had charge, but when tested, showed zero life in the battery. with the bad battery, the truck would start up, then immediately stall out. we popped a new battery in, and its run like a top since.

ttms91xj said:

forgive me if im wrong, but the battery is part of the electrical circuit with the alternator, right? so why would removing it show a problem? if u pull that part (or any part) of the circuit out, wouldnt the circuit be broken no matter what? we had a battery in my work truck go bad...it still had charge, but when tested, showed zero life in the battery. with the bad battery, the truck would start up, then immediately stall out. we popped a new battery in, and its run like a top since.

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The battery is not part of the ciruit as you're thinking. It's in parallel with the alternator, not in series, so theoretically, the alternator should be able to run with the battery out once the vehicle starts, although many electronic controls will misbehave without the filtering effect of the battery, because the alternator will provide overvoltage and chopped DC.

Way back in the dreamtime, when alternators were first made standard equipment by Chrysler, this was even a selling point in their ads: they took a Valiant or some such vehicle and ran it without a battery across country. DC generators cannot put out enough current at idle to do this reliably, but an alternator can. This is not recommended, though, because it can cook the diodes. I guess the old Chrysler alternators were pretty tough. There were no electronics in a 60 Valiant, and even the voltage regulator was mechanical.

when i got my jeep the battery had exploded from being jumped backwards and fried 2 caps in the compass circuit.

I thought I knew enough about this until my boss mentioned 1) the late model don't disconnect thing, and 2) "This is not recommended, though, because it can cook the diodes" running without a battery.

What we're seeing here is "old school 35 amp alternators in points equipped cars" diagnosis used on a 120 amp electronified late model. Please enlighten the old fart who told you this from spreading it further. I had to stop, too.

Now the newer hi amp alternators need a full 12V to operate the windings and electronic regulator; ergo, a fully charged battery to check alternator operation. A flat 0% charged battery requires 24 to 48 hours at 10 amps to recover (try explaining that to a one car wage earner Sunday afternoon.) The alternator will not do the job - it will stress the diodes and sulphate the cells from overcharging at too high a rate - unless it self terminates early.

I learn something new everyday.