Alternator question?

recently the amp light wouldn't go out after starting the Jeep. 225 V6. I pulled the alternator and took it down to my flaps and had it tested. It was bad they said. I took it down to a local alternator shop and had it rebuilt. The jeep has been running around for a couple days but the amp light is back on. I pulled the positive battery cable while it was running and it died immediately. I have a multi meter, what do I need to test and what values am I looking for? Thanks as always!

 

Are you talking about the original Motorola? Unless you are wanting to stay completely original you should think about upgrading to a GM 10si or 12si alternator which is easy to do and very beneficial.

IMO you shouldn't send too much money on the Motorola unless you want to be completely original.

Here is a threads when I made the change a couple years ago
10si or 12si alternator on dauntless

 

Take it back to the alt repair shop along with the regulator. They should test both together.

 

the local auto parts store . should test it for free . regardless where you bought it or repaired . now some alternators the amp light will be on until you give it a little gas (low idle)and then stays off .

 

Looks like a bad alternator. Surprised because the local shop who rebuilt it is very reputable. I pulled the alternator and also the voltage regulator. I'll update everyone tomorrow.

 

I don't recommend to customers to use the local auto parts stores for alternator testing unless the tester can give both voltage and amperage test results. Many of these "test results" just check for output, but not how much output. For example if the alternator puts out 12v and 20 amps it tests ok even though max might be rated 14.7v and 85 amps.

 

nickmil has it right.

 

Noteworthy comment here. It is not advisable to disconnect the battery while the motor is running. May be OK with an older mechanical regulator but you'd fry a newer alternator.

 

Yeah, you can pull a battery cable with engine running if you have a generator, but don't do it with an alternator.

 

The alternator and voltage regulator both checked out just fine at the repair shop. They let me come back and watch while they ran all the tests. I will double check the wiring to the alternator, the idiot light and general grounds and see if that doesn't fix my problem.

 

There were several very important questions asked but were never answered by you. What alternator / regulator do you have? Is your wiring harness original? Are you making sure the belt is tight enough that it is not slipping. Pic's are always a great help.

 

Sorry Walt! It's the original 56 amp Motorola. The regulator also appears to be original or an original replacement. Yes, the wiring is all original. Yes, I'm positive the belt isn't slipping. As soon as I drop it back in, I'll post pics. Thanks!

 

How were you able to tell? The belt should have about how much play at the longest run?

 

The original Motorola alternator was only 30-35 amp in the stock cj.

 

Maybe I meant the Delco? It's the optional heavy duty one. A single blade for the field connector. It's also on a Jeepster Commando if that makes a difference.

 

A check with your multimeter should tell you if your alternator is performing--therefore your belt is not slipping, etc.

Multimeter set to 20 volt DC range place proper leads to battery terminals (red to +/black to -) --with engine off reading somewhere around 12.5 volts --with engine running somewhere near the 13.5 - 14.2 range. May need some rpms to get output.

Carefully, as always, about moving parts with engine running!

 

Proper belt width is important. The belt grips the pulley on the sides. If the belt is riding in the bottom of the groove then it will slip. The top of the belt should be at or slightly above the top of the pulley. If you can spin the alternator fan by gripping and spinning with your fingers then it's too loose.