Batt. Draining/Alt not charging

June 07, 2010, 09:09:32 PM

This is in an 87 5.0 car. This is in my brothers 87 Grand Marquis. The alternator isn't charging the battery and the battery dies within about 5-10 minutes after starting.

So far, he has replaced the alternator, and had the battery tested.

I disconnected the neg. battery cable and hooked up a test light between the neg. post and neg. cable...... light does not come on.

Touched a non magnetic screwdriver to the laminated part of the alternator with key off - no magnetism, with ket on the screwdriver is attracted to it.

We jumped the car and while running I used a voltmeter and saw there was a steady drop in voltage and the car would eventually die after it got around 6 or so volts.

Battery light comes on when key is in on position but goes out after it is started.

I am thinking he has a problem somewhere in his wiring, maybe a fusible link somewhere, but I haven't gotten a chance to test this yet. Is there other things I should be testing for? (Well I'm sure there is)

Batt. Draining/Alt not charging

Reply #1 – June 08, 2010, 08:17:12 AM

Try to replace voltage regulator. Can you tell me if there is some change in voltage after start? Is the another alternator new, or in good condition?

There won't be any magnetism while the engine isn't running. Magnetism is made by the field (some voltage between ground and F connetor). This should be the first to control - voltage on the field connector.

Batt. Draining/Alt not charging

Reply #2 – June 08, 2010, 03:09:42 PM

Quote from: Trinom;324668

Try to replace voltage regulator.

The regulator is internal on ALL 5.0 Ford/Mercs from '86 up, there is no external regulator excepting for fleet duty vehicles with the 100A alt...

Batt. Draining/Alt not charging

Reply #3 – June 08, 2010, 06:09:40 PM

Quote from: TurboCoupe50;324710

The regulator is internal on ALL 5.0 Ford/Mercs from '86 up, there is no external regulator excepting for fleet duty vehicles with the 100A alt...

And Mark VIIs

Batt. Draining/Alt not charging

Reply #4 – June 08, 2010, 06:33:33 PM

Quote from: Trinom;324668

Try to replace voltage regulator. Can you tell me if there is some change in voltage after start? Is the another alternator new, or in good condition?

There won't be any magnetism while the engine isn't running. Magnetism is made by the field (some voltage between ground and F connetor). This should be the first to control - voltage on the field connector.

The alternator is a new (not reconditioned) unit. After having the battery charged and load tested (by the auto parts store) we hooked it up, started it, I put my voltmeter to the battery and it constantly lost voltage - when the car finally dies (at around 6 or 7 volts) the voltage on the battery jumped up around 10.5 volts.

While running, we pulled the connector on the side of the alt (2g alt) and the voltage read steady at around 11 or so volts for a while, then after a few minutes started dropping again, but at a much slower rate.

Batt. Draining/Alt not charging

Reply #5 – June 08, 2010, 07:55:35 PM

when you first put in the new alt. was that battery fully charged? Apparently according to auto-zone, if you try to start these cars with out having a fully charged battery it can smoke a new alt.

Batt. Draining/Alt not charging

Reply #6 – June 08, 2010, 07:57:42 PM

Yea, they fully charged the battery before they did the load test, and made sure it was charged afterward.

Batt. Draining/Alt not charging

Reply #7 – June 08, 2010, 09:45:26 PM

possibly two things, 1 you got a bad alt. have auto parts store test it. most of them have a tester for them. suggest taking to another store other than where you bought it from. Second is possibly a grounding strap is shorting out in engine bay. Over the 9 years I have been a professional mechanic I have seen a lot of things happen to do this. most of the time it was a grounding strap that had shorted out or was frayed really badly. I have seen shorted out regulators, wiring harness, there is a whole bunch of stuff it could be but I would recommend have the alt tested first. You can get a bad new alternator.

Batt. Draining/Alt not charging

Reply #8 – June 08, 2010, 10:11:05 PM

Quote

You can get a bad new alternator

That is very true. The first 2 reconditioned ones we bought from autozone were bad. We bought a new one from oreilly's and went to advanced auto parts to have it tested before we even put it in the car. Are there any specific places you could tell me where these grounding straps would be? The regulator is internal, so that checks out as long as the alternator is good. There are a few spots in the wiring i need to check, they come off the top connector, they are the bigger black wires that come out of 2 pins on the alt connector then go into a fusible link connection. I'm not sure if I should be checking for voltage coming out of them, but right after the fusible link the wire is a little bare, and I can see inside the rubber part and it is a little corroded.

Batt. Draining/Alt not charging

Reply #9 – June 09, 2010, 12:34:05 AM

that may be your problem right there. if the fusible link is fried it will stretch like a rubber band when you pull on it from both sides of the link ( the black cylinder part of link) if it doesn't pull completely apart.. If that is shorted out it will cause a drain on the system. If you think that is what it is you can cut the link out and test it by reattaching it with butt connectors. this is a temporary fix. it should not be left this way!! Most cars have a grounding strap on the passenger side of car placed between the frame rail and the engine block. sometimes is down under where the ac unit is closer to the firewall. It is a flat ribbon looking strap usually. Best of luck electrical diag. sucks.

Batt. Draining/Alt not charging

Reply #10 – June 09, 2010, 12:46:45 AM

Pull the alt out of your 86 as well as the battery and see if anything changes. If your voltage is dropping while the car is running, the alt isn't doing anything, or very little. I have had several "new" alts go bad after about 1 year. I have had one for about 2 years that I pulled out of my last car, and so far no problems. You should be around 13.5 volts at idle with everything one and maybe 14 with everything off. You need over 12 volts in order for your battery to be charging.

Batt. Draining/Alt not charging

Reply #11 – June 09, 2010, 09:17:27 AM

I like your troubleshooting techniques.

Quote from: 20thanniver-ls;324631

This is in an 87 5.0 car. This is in my brothers 87 Grand Marquis. The alternator isn't charging the battery and the battery dies within about 5-10 minutes after starting.

So far, he has replaced the alternator, and had the battery tested.

I disconnected the neg. battery cable and hooked up a test light between the neg. post and neg. cable...... light does not come on.

Touched a non magnetic screwdriver to the laminated part of the alternator with key off - no magnetism, with ket on the screwdriver is attracted to it.

This means the alternator field current is being turned on. This is good.

Quote

We jumped the car and while running I used a voltmeter and saw there was a steady drop in voltage and the car would eventually die after it got around 6 or so volts.

This sounds like you are running on the little bit of charge the battery has as a result of the jump start. No alternator output.

Quote

Battery light comes on when key is in on position but goes out after it is started.

This means the alternator has a stator voltage output and causes the regulator to turn off the battery light. This is good.

Quote

I am thinking he has a problem somewhere in his wiring, maybe a fusible link somewhere, but I haven't gotten a chance to test this yet. Is there other things I should be testing for? (Well I'm sure there is)

I think you are right in suspecting the fuse link. More on this later.

Quote from: 20thanniver-ls;324724

The alternator is a new (not reconditioned) unit. After having the battery charged and load tested (by the auto parts store) we hooked it up, started it, I put my voltmeter to the battery and it constantly lost voltage - when the car finally dies (at around 6 or 7 volts) the voltage on the battery jumped up around 10.5 volts.

Did the voltage jump up when the car stalled or when the key was turned off?

Quote

While running, we pulled the connector on the side of the alt (2g alt) and the voltage read steady at around 11 or so volts for a while, then after a few minutes started dropping again, but at a much slower rate.

If you pulled the regulator connector, you took the load of the field current off the battery.

Quote from: 20thanniver-ls;324729

Yea, they fully charged the battery before they did the load test, and made sure it was charged afterward.

This is confusing. The car should run for a long time on a fully charged good battery, even with no alternator output. Charge the battery and check it a couple of hours later to see if holds a charge of 12.5 volts.

Quote from: 20thanniver-ls;324751

There are a few spots in the wiring i need to check, they come off the top connector, they are the bigger black wires that come out of 2 pins on the alt connector then go into a fusible link connection. I'm not sure if I should be checking for voltage coming out of them, but right after the fusible link the wire is a little bare, and I can see inside the rubber part and it is a little corroded.

The two bigger black wires are the alternator output and should be hot at all times. With the key off pull the connector and check for battery voltage on the black wires. If there is no voltage, the fuse link is blown. The other end of the fuse link is on the battery side of the starter relay.

Batt. Draining/Alt not charging

Reply #12 – June 09, 2010, 05:43:24 PM

Got it figured out. One of the wires after the fuse link was fried........ Thanks for the replies guys.

Batt. Draining/Alt not charging

Reply #13 – June 09, 2010, 08:13:21 PM

No Problem glad we could help.