Bad Alternator??

[michael1989]

My bronco won't start as if the battery is dead. So I jumped it and it still did the same the same thing, the starter makes about 1/2 a revolution then it stops. Is the alternator bad or is the battery just dead beyond charging.

 

[NaturalRampage]

Heya. Lets see if the battery is in good shape first. Use a volt meter to test it. If its at atleast 12v then the battery is good. Next check the connections from the battery, positive goes to the Solenoid and the negative goes to the motor as a ground. Let us know how that goes and keep us updated.

Edit: If you have a battery charger keep it on over night and try again the next day.

 

[Bully Bob]

You're not giving us much info. so as to give accurate advice.

Battery history.? Jumped it with what...?

Like Rampage said "you need to do some testing"

Another option is to take the bat. & alt. to your auto parts store & let them load test, etc.

Corroded connections are often the culprit.

 

[michael1989]

I dont know the history on the battery because I just got the bronco and there isn't a date printed on the batt. I do know it was giving a good 14 volts before. It was jumped with a 92 gmc with a brand new alternator and good battery. Also when the two batteries are hooked up my guage reads that it is getting 16 volts until I try to crank it then it drops to under 8.

 

[Bully Bob]

"I do know it was giving a good 14 volts before"

I'm assuming this was 'via' a volt meter or the dash gage.

My guess would be a 'dead cell' in your bat.

(I've had a dead cell disallow help fr. a jump start before)

The 14 volts was prob. with the eng. runn'n & reading the dash gage..?

This would mean the alt. is supplying that voltage.

 

[Rons beast]

A voltage drop to 8 volts during cranking, and staying at that level after, indicates a week battery.

To be sure, it needs to be fully charged, and load tested. You could get a cheep specific gravity tester. It will make a bad cell show up easily, ( any cell testing below 1250, when fully charged.)

You need a good battery to correctly check the alternator and starter.

good luck and let us know what you find.

ps battery to engine and frame grounds should always be checked. Notoriously bad on Broncs.

 

[Seabronc]

ps battery to engine and frame grounds should always be checked. Notoriously bad on Broncs.

Right, take them off, clean them up and put them back on. Also check the condition of the cable, especially where the cable connects to the lug. there should be no corrosion at that joint, if there is, replace the cable.

Good luck,

 

[michael1989]

I tested it with a multimeter by putting positive on the solenoid and negative on ground and got nothing. My next step is going to pep boys and testing the alternator and battery.

 

[Rons beast]

What "it " did you test?

 

[michael1989]

The battery. Positive on starter solenoid and negative on the motor.

 

[Bully Bob]

Mike.,

IMHO At your age, (17) you would be well served enrolling in an automotive class at school. Also., you need to get a book relating to your vehicle, & read it.

There's concern that you could hurt yourself, or your vehicle.

You will find the classes quite "fun" & the book very interesting..!!

Folks on this board are always ready & willing to help but you may be on here for months...some may lose interest. Just say'n.... >< <'>

As to your last post.., one side of the solenoid is "0" volts until the key is turned to start.

 

[Krafty]

take the battery terminals off and clean them out really well with a copper fitting brush,( it gets inside the connectors very well) then clean up the posts and reconnect. i've been plagued with low voltage issues over the years just cause of a bad connection.

 

[Krafty]

if the battery was fine and was fully charged when it was parked then it is NOT the Alternator. if the battery reads 12-13 volts then its usually good, when voltage drops off when you try to start it then that means somewhere between your battery and your starter you have a bad connection or bad ground.

Basic electrical lesson, a circuit with no resistance ( good connections), include an amperage load ( starting or using accessories), the circuit will have full voltage ( full flow of electrons) with or without the amperage load.

a circuit with High Resistance ( faulty connections and the like) with no amperage load will have full voltage, once an amperage load is drawing power the bad connections will restrict the flow of electrons (which is your voltage) and your voltage will drop failing to produce the power required for the amperage load. once the load is removed the voltage reading will come back up

clear as mud?

 

[michael1989]

So if the terminals are too dirty would that be a reason it won't accept a jump start?

 

[Krafty]

it could also be a connection further along the system, I would also look at the wire going to the starter and your ground wire on your battery where it bolts to the engine block.

 

[Krafty]

the low voltage even with another battery giving it a boost is a telltale sign of a bad connection. the only hard part is finding the one connection causing the grief. go over every wire and connection between the battery and starter, take apart and clean every connection, do a resistance or ohms test on each wire. anything above 0.1 ohms of resistance means its bad.

P.S only take one connection apart at a time so you don't accidently get anything mixed up.

 

[Rons beast]

I reread your original post. There are some things you MUST do or you will chase this problem around for a long time.

Check the battery acid level if it is not a sealed battery. If it is ok or slightly low add water, and fully charge the battery. If the battery is very low on acid, or empty, or the case is bulging, DO NOT ATTEMPT TO CHARGE IT! The battery is bad, and can be a danger. Get a new battery.

Unless the battery cables are new, get new ones. Positive, battery to solenoid and solenoid to starter. The battery ground to engine must be replaced too, and any other ground straps. battery to frame, frame to body, etc. The cables can be a hidden problem that must be eliminated before any other checks of the electrical system. Cables are cheep compared to starters and alternators, both of which have been replaced by well meaning people when the cables are the problem.

Once you have good cables and a fully charged battery, check the voltage across the positive and negative posts. You should have 12 volts minium. Have someone crank the engine, if during cranking the battery voltage imediately drops below 10 volts, the battery is bad. If the drop is gradual, there is a good indication the starter is the problem.

If the battery passes these tests and the engine can be started, check the charging system. With the engine running at about 1000rpm and all accessorys on you should read 13.7 to 14.2 volts. If you have that, the alternator is ok. If not then the lack of proper charging must be diagnosed. More on that later.

Remember, all these tests are based assuming the cables are good.

check each system one at a time.

GOOD LUCK.

Let us know what you find.

 

[Seabronc]

Once you have good cables and a fully charged battery, check the voltage across the positive and negative posts. You should have 12 volts minium. Have someone crank the engine, if during cranking the battery voltage imediately drops below 10 volts, the battery is bad. If the drop is gradual, there is a good indication the starter is the problem.

Remember, all these tests are based assuming the cables are good.

check each system one at a time.

GOOD LUCK.

Let us know what you find.

Ditto on Ron's post

Do what you were requested to do. You were told this several posts back and as far as we can tell you never did anything with the cables and connections. Where ground cables are connected clean the area they connect to using a little Emmery cloth, (where the ground [battery -] connects to the engine block, where the ground connects to the frame, both ends and even the ground strap from the driver side of the intake manifold to the fire wall). There is not much point in us giving you a suggestion if you do not do it and report the results.

 

[michael1989]

I cleaned the solenoid connections and the ground cables. I hooked a good battery up and cranked the engine ans it started just fine but I'm still questioning about the alternator because there was water on top of the battery and the voltmeter in the dash jumps rapidly between 16 and 18 when the engine is idling at about 1000 rpms.