Low amp reading

Low volt reading

I have been dealing with a problem all weekend and cant seem to find and fix it. I have a 89 mj 4.0 with low volt reading in the red for over two weeks now. didnt do anything about, thought it might be a bad gauge because the truck was always starting up with no problem until this past thursday morning.
I went out to start it up and out of nowhare All I got was the dreaded Click, Clicc, Click and then nothing. I thought it was the battery (it was old) so I replaced it and the next day it did the same thing and the gauge never did move. I check the Alternater buy using a test light between the ground post and cable. I pulled the plug on the alt. and the light never went out so It was good. I tested for shorts the same way while pulling the fuses to find a possable short that might be draing the battery but found nothing. I put a meter on the battery and it was reading 11.8. Im stumped so here I am talking with you guys.
Does anybody have any ideas, Thanks for your time...........Randy

First things first - that's a voltmeter, not an ammeter. While an ammeter is typically a little more useful for "state of charge" than a voltmeter, a voltmeter is more common (since an ammeter has to be hooked in series with the total vehicle electrics.)

Next, get out your voltmeter and do the following:

Check battery voltage, KEY OFF. You should get 12-13.8VDC at the terminals. Recheck at the output post on the back of the alternator - the reading there should be within .2VDC (lower) of the direct battery measurement. A low reading at the back of the alternator indicates a problem with the alternator cable leading to distribution. NO voltage there probably means a popped fusible link wire.

Check battery voltage, CRANKING ENGINE. You should see 9.6VDC or better.

Check battery voltage, ENGINE RUNNING. This should be 13.2-15VDC. Recheck at the alternator output post - this time, it should be no more than .2VDC higher than the battery terminal voltage.

Let us know what you find out. You can check the link at the bottom of this post for cable and/or alternator upgrades...

5-90

Glad you came. First off the meter reads volts not amps. Amps is current flow. The meter actually just shows the voltage, not how much current is being drawn. Not trying to bash, just get you talking the right lingo.

It appears that your problem is that the battery is not getting charged sufficiently. It could be a bad battery, but charging issues are more common. First do the normal maintenance type things. Remove and clean the battery cables. Use baking soda and water to remove corrosion. Check the connection to the alternator for corrosion as well. Check that the serpentine belt is tight and not slipping. A loose belt can make the alternator not charge enough to keep the battery up and going. Check that the battery has water in it. A low cell can cause the battery to have issues. Your symptoms do not fit a low cell, but get in the habit of checking the battery several times a year. Then jump start it and see if the voltage comes up to normal. If it doesn't you can go to Autozone and they have a tester that can tell you if the alternator is putting out current and is good. They can also check out the battery. They pull it out to the car and do the diagnostic for free.

The voltage regulator in the 89 is built into the alternator, so if it isn't charging, replacing the alternator can normally fix it.

If your Alt is putting out 11v it will light your light but will never charge your battery.

Re: Low volt reading

ok here we go guys.
I had a good day driving to work. started right up this morning and started up to go home, when I came home I did the check that you guys wanted me to and this is what I got. Parked 12.5 at bat. and 12.2 at at he alt. not running. During start up its 10.8 and as its running 11.2. I hope this helps you. Im still getting a low reading at the "VOLT" gauge.
I was reading a page about somebody replacing factory wires with 4 gauge wires for better electric flow. Im going to go clean up some connections and see if that helps any. Thanks for your time.............Randy

Re: Low volt reading

2wdxj said:

ok here we go guys.
I had a good day driving to work. started right up this morning and started up to go home, when I came home I did the check that you guys wanted me to and this is what I got. Parked 12.5 at bat. and 12.2 at at he alt. not running. During start up its 10.8 and as its running 11.2. I hope this helps you. Im still getting a low reading at the "VOLT" gauge.
I was reading a page about somebody replacing factory wires with 4 gauge wires for better electric flow. Im going to go clean up some connections and see if that helps any. Thanks for your time.............Randy

Click to expand...

Your battery is not charging, your ALT is putting out only 11v it must be 12.75 to 14.75 anything less it will not charge.
Heavier wires will not help with a stock alternator.

True. Fix the charging problem first.

The 89 (actually, 1987-90) uses a Delco CS-series, internally-regulated, alternator - which is available nearly anywhere.

First thing to do is clean everything up, make sure all your connections are good, and ESPECIALLY check the battery ground to the engine block (near the distributor) and that stupid little ground strap at the driver's side rear of the cylinder head. Make sure those are okeh.

Make sure all connections are clean, reassemble, and retest.

The 10.8VDC at crank is good, but the 11.2 KOER is not. It sounds to me like your alternator is going silly - so think about replacing it. Changing cables won't help if you're not charging in the first place, so prioritise your repairs. If you're getting anything less than 12.6VDC running, with minimal accessories turned on, you're driving on the battery.

5-90

Im going to my local Auto Zone and have them put there machine on it befor I start tearing anything apart. I replaced the alt just over a year ago and it was a PITA to put in. I feel you are right and I thank you guys for your input but one more teast and then I will get my hands dirty. Not that I mind?!

If Im going to replace the alt I would like to get a better then stock Alt. What do you guys suggest? I still want to change out the wires as well. Let me know what you guys think and thanks.............Randy

2wdxj said:

Im going to my local Auto Zone and have them put there machine on it befor I start tearing anything apart. I replaced the alt just over a year ago and it was a PITA to put in. I feel you are right and I thank you guys for your input but one more teast and then I will get my hands dirty. Not that I mind?!

If Im going to replace the alt I would like to get a better then stock Alt. What do you guys suggest? I still want to change out the wires as well. Let me know what you guys think and thanks.............Randy

Click to expand...

Have yours rebuilt at a generator shop and converted to Hi Output.