1995 Ford Explorer Battery/alternator/starter?

  • 3.2L
  • 6 CYL
  • 2WD
  • 100,000 MILES
It set all winter. This summer I could jump start it so a4 weeks ago I put in a new battery. & All was good. It set two weeks & now it will only click. I jumped it, Taped on the starter while trying to start it cheeked for corrosion (None to be found) & replaced the battery cable ends out of fruition Took the battery out & had it cheeked & it is fine. I used to disconnect the neg. Battery cable & the car would stop running I new it was the alternator but can't do that now. No clicking I new it was the starter or solenoid. I don't know what to do. Can any one help I can't spend what I don't have.
Do you
have the same problem?
Tuesday, September 1st, 2015 AT 1:30 PM

1 Reply

First of all, just let me say, ...



Every year I did a demonstration on the generator test bench for my students to show what can happen when you do that. It was real easy for the voltage to reach over 35 volts. That WILL destroy any computer on the vehicle, the generator's internal diodes and built-in voltage regulator, and any light bulbs that are turned on.

The thinking is that if you disconnect either cable and the engine stays running, the generator must be working but a lot of them will stop working due to the voltage regulator responding to the dips in the "ripple" voltage being produced. That will make a perfectly good generator appear to be bad so that test is not valid.

If a mechanic is caught pulling this stunt he will typically get one verbal warning. For the second offense he will be fired. It's that big a deal.

Some generators respond to the high points in the ripple. That momentary higher voltage goes right back to the field winding and creates a stronger magnetic field. That stronger electromagnet creates a higher output voltage which again creates a stronger electromagnet. It's a vicious circle and voltage can keep on rising until something gives out. The main thing that smoothes out that ripple so it doesn't affect the voltage regulator or the generator is the battery.

Three things are needed to generate the output current. They are a magnet, (electromagnet, in this case), a coil of wire, and most importantly, movement between them. That's why the belt needs to make it spin. One thing that can save you from doing damage by removing a battery cable is not raising engine speed. Generators are relatively inefficient at low engine speeds and their output voltage is less likely to rise to dangerous levels, ... As long as you don't raise engine speed.

One other thing to keep in mind is batteries give off explosive hydrogen gas. Regardless if your generator is working or not there is going to be a big spark when you remove a battery cable with the engine running. Either the generator's current will be recharging the battery, and that can be up to 20 amps, or the battery is going to be supplying the car's electrical systems, and that can easily be over 30 amps. That kind of current is going to create a big spark when a connection is broken or reconnected. Small arc welders run as low as 40 - 60 amps and look at the sparks they create. The reason we don't hear about more battery explosions is because people are careful to not disconnect the cables when there is current flowing through them. It's also why there are huge warning labels on all battery chargers to be sure they are turned off before connecting or disconnecting them from the battery.

Another common generator problem is one defective diode out of the six. You will lose exactly two thirds of the generator's capacity but system voltage will remain normal or it could even be just a little high from the voltage regulator responding to the greatly increased dips in the ripple voltage.

It's always a good idea to wear safety glasses when working around car batteries, but if you still insist on removing a cable while the engine is running, a face shield makes more sense, and have plenty of water on hand to wash any acid off the vehicle's paint.

For '95, Ford has a really nice generator design that allows testing right on the back of the unit. Only Chrysler alternators are easier to diagnose. Unfortunately the engineers don't really care about ease of service on GMs and many other brands.

The way you tell if the charging system is working is to measure the battery voltage while the engine is running. It must be between 13.75 and 14.75 volts. There still could be a bad diode though. You need a professional load tester to test for that. Ripple will be very high and the most output current you will get will be one third of the generator's design value. That is not enough to meet the demands of the electrical system under all conditions so the battery will have to make up the difference, until it runs down. You still could have a generator problem. A professional load test will show the condition of the generator.

Okay, now to get back to the original problem, be aware there a number of computers on the truck that are constantly drawing current from the battery. Unless specified differently by the manufacturer, that can be up to 35 milliamps, (.035 amps). At that rate a battery can only be expected to remain charged enough to crank the engine fast enough to start after sitting for three weeks. You might get a little more time with your truck, but much more than that you can expect to have to charge the battery or jump-start it.

So you decided the generator is defective and the starter or solenoid failed at the same time. From what you described, I suspect you have nothing more than a discharged battery. Charge it at a slow rate for an hour or two, then if the engine still doesn't crank, you'll need an inexpensive digital voltmeter and we'll take some readings to locate the cause of the problem.
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Tuesday, September 1st, 2015 AT 1:59 PM

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