'98 Mustang Charging Problem

Maintenance/Repairs
1

The car: '98 Ford Mustang 6 cyl with 145,000 miles. When cold, it does take quite a bit of cranking before it finally turns over.

The short version: The battery is not charging. Replaced alternator. Battery and new alternator both test good.

And the Long Version of the problem I’m having:

6 months ago, on the way home from work, I ran out of gas. While I walked to get a gas can, I left the lights on. The battery was too dead to start the car by the time I returned, so I got a jump. A few days later, the power was dead and I realized that the negative battery cable connector was loose. So I tightened it and everything was good.

6 weeks or so ago, my daughter took the car out, and it wouldn’t start for her on her return trip. So I went out thinking that the cable had come loose. That terminal (the negative) was badly corroded. I jumped it, got her home, and the next day I cleaned the terminal with baking soda and water and reconnected the cable. The connector was pretty loose, so I tried to tighten it and only wound up crimping it to an oval shape. But it went on tightly and I thought I was good.

A few days later, the battery was low again, so now I thought that the connector was not making a good enough connection. So I went out and bought a new connector. I had a hard time getting the old one off, and finally had to take a hacksaw to it. I got the new connector on and it ran fine.

A few weeks later, it wouldn’t start again. We jumped it and got it home. Everything looked good and well-connected. I jumped it again and took it to Les Schwab to have the battery tested, thinking that it was old and not doing well. They said battery tested fine but that the alternator failed. The guy there convinced me that I could replace the alternator myself.

So the next week I bought a new alternator from AutoZone and installed it. I’m pretty sure I did it right. The belt is tight and the alternator spins at high speed. It doesn’t wobble or seem to vibrate.

I took the old alternator back to AutoZone and had them test it on their machine. It failed. So I thought I was good. I jumped it and went on a nice highway-speed drive for an hour. I drove it for a week before I had any further problems.

But then it started turning over weakly. Sometimes it would start before running out of juice, sometimes not. I jumped it four or five times that week.

Last week, I unplugged all of the wires out of the alternator and replugged them. I pulled out all of the fuses and checked them. Then I took it back to Les Schwab for another test (after jumping it). They said it tested fine, though a little low. He offered to put it on the charger for a few hours and test it again. And it tested fine again.

So, I hoped that the unplug-replug had worked and drove it this week. But it didn’t. It started weakly on Wednesday morning, and wouldn’t start Wednesday night.

The battery doesn’t seem to get worse if I leave it overnight, or even for a few days. If I jump it, drive it for 30 minutes it has enough juice to immediately restart the car (it catches and starts running right away though), but it won’t have enough electricity to run the starter long enough in the morning. This wasn’t a problem before.

So after that long description, do you have any ideas? Did I get a bad alternator? Need a new battery? Do I need to trace down a broken wire?

Any help you could offer would be of great help!

Thanks,

–Vecna

2

Check and clean the ground cable connection from the battery at the engine block or wherever.

3

When you jump it are you putting the neg from the good battery to your block or are just going across your battery posts ( a no no ). if going to your block then I would do what Barkydog said first.

If going right across your battery terminals you need to get a cheap voltmeter and measure the voltage when the car is running, should be no lower than 13.5 up to about 14.5 volts. If this is ok means your alternator is functioning.

Sometimes a battery will test good on a tester if it has a surface charge on it and its best to let it sit for about an hour then test it. If your alternator is not working, you would not get far after jumping a dead battery. Trying to charge a dead battery is bad for the alternator and can damage it but people do it everyday without problems in an emergency situation like leaving your lights on in a parking lot.

What are you supposed to do here ? Take out the battery and have someone drive you to get it charged and wait a few hours or simply jump it and drive home ?

I learned from experience when you start getting corrosion on battery terminals it is due to the battery out gassing by being over charged. How this happens is, you have 6 cells in series giving you about 12.6 volts. If you develop a weak cell then the alternator is trying to charge a weak battery so the 5 good cells are being overcharged. This out gassing is what starts the corrosion on the terminals. I just replaced a 6 year old battery in my Mustang GT and had corrosion on the terminals…

I checked it with a hydrometer ( 2.00 at wall mart ). 5 cells showed about 100% charge and one cell only 50% as car was getting slow to crank. If your battery is more than 3 years old I would suspect that if all connections are clean and good and alternator is within specs charging voltage wise.

4

Are you sure when this happens, it is due to the battery being dead? Did you have the battery load tested at that point? B/c it may be the alternator and battery are fine, and the problem is in the starting circuit. It may be you just need a new starter motor. Bad contacts in the starter motor selenoid are a common problem and will cause this for example.

Next time you get slow or no cranking, remove the battery and have it load tested. If it tests good, you know the problem lies elsewhere, and that the battery and alternator are ok.

Also, most retail auto repair and parts stores will test the battery and charging system on the car. My local Sears will do this for free for me. That’s the best way to confirm both the battery and alternator are working as installed.

If the battery is drained, it could still be that the battery and alternator are good, but there is something else – like a short circuit due to wire insulation problems – draining the battery. Best of luck.

5

If it was the starter motor why does the car start right up with a jump ?

6

You should never try charging a low battery using the alternator. It will put excessive stress on the alternator output and possibly shorten the life of your newly replaced alternator. It is also a good idea to replace the battery whenever installing a new alternator since they work together. If your battery connections are clean and making a snug connection (not over tighened, as a lot of folks make that mistake and stretch the clamp) and the fan belt is tightened properly you might have a problem with the alternator output or the connection between it and the battery. There should be less than a .5 volt of difference between the output connection of the alternator and the positive battery post with a good load on the system. The alternator should have between 13.5 and 14.8 volts output while the engine is running areound 1,500 RPM with a good load on the system. I suggest you take it to a shop where they can do a active load test on the charging system. It will tell the real story about how well the charging system is performing and if it can handle the full rated output. I would also replace the battery if it is more than 3 years old. Especially if you live in a cold climate.

7

Agree totally with Cougar

8

@Vecna I read your post and while it is informative, I have one question

How old is that battery?

If it’s 5 years old (or older), I’d replace it immediately, REGARDLESS of how it tests

Perhaps the battery simply can’t hold a charge

And even if that’s not the end of the problems, at least you know the battery is fresh

9

I remember having a battery that would start the car when cold, then as engine temps would increase and then engine shut off ( especially in the summer ), it would raise the battery temperature under the hood and would not crank…batteries can act in funny ways…jump it and would start right off…gave the same symptoms of a starter being heat soaked but rarely and issue with Ford 5.0’s as with some Chevy small blocks that required a heat shield on the starters due to exhaust manifold routing to the cat and muffler.

10

I would buy a OEM battery cables and not one of those cheap after market connectors. If the connection is not perfect, you can not charge the battery properly. Also. the starter requires all the battery current to run and they only make partial contact. The reason it may start with a jump is that you are putting a lot more power to it. All grounds need to be cleaned and if the neg cable it corroded it needs replacement too. I have had starters work on a jump and not start intermittently before. You are definitely in the time frame where a starter can fail. Do not buy re-manufactured parts from AutoZone or Advance or any other cheap place. They have lifetime replacement warranties, but who wants to keep doing the same job over & over. Buy NAPA or OEM.

11
@Howie32703 writes ... "If it was the starter motor why does the car start right up with a jump ?

If the jump is done with the current supplying car running, the voltage will be higher. 14 volts, vs 12.5 volts. Even if the current supplying car’s engine was turned off, as the combined output resistance of the two batteries in parallel is less than a single battery, it would still provide add’l voltage to the starter motor. That add’l voltage could be enough to overcome the resistance of somewhat corroded starter selenoid contacts.

The good thing about theories like this is that it can easily be tested. To test this theory out – that the battery and alternator are actually good, and the problem is in the starting circuit – the OP could ask the mechanic to measure the voltages at both terminals of the starter motor during attempted cranking. (Do this under normal operating conditions, not during jumpstarting.) If either is below 11 volts, that would be an indication of something wrong anywhere from (and including ) the battery, the ignition switch, starter relays (etc) right up to the starter motor. If both are above 11 volts, even better if above 11.5 volts, during attempted cranking, and the engine doesn’t crank robustly, that would be an indication of a problem with the starter motor or more likely the starter motor selenoid contacts. It’s possible to test the starter selenoid contacts in a similar manner. Most starter motors have a third terminal available where you can measure the voltage after the selenoid contacts.

12

+1 with Cougar