Charging Issues

[dbc28092]

I have a 1984 C30 with the 6.2L diesel. I bought the truck in June and have been trying to work through some issues to make it dependable transportation. I can't seem to figure out the charging issues I'm having. I realized early the batteries were not keeping a charge. The batteries were 8 years old so I replaced them. Still couldn't keep a charge.

I tried checking the voltage with a multimeter while the engine was running...it only showed 11-12 volts. I removed the alternator and took it to AZ for testing. They tested it twice and it failed both tests. I bought a remanufactured alternator and put it on the truck. Batteries still aren't charging. Multimeter still shows 12 volts with engine running.

I have three ideas for what might be wrong. 1)There is a wiring issue.  2)I got a bad alternator from AZ.  3)I've done someting wrong when installing the alternator.

Any ideas or suggestions?

[zieg85]

Take the alternator back in to AZ.  They typically sell junk when it comes to starters and alternators.  Have them test it out.  Should be 13.2-14.8 VDC output

[bake74]

Take the alternator back in to AZ.  They typically sell junk when it comes to starters and alternators.  Have them test it out.  Should be 13.2-14.8 VDC output

     Take your truck with the alternator back and have them test it, also look in the tech section and do a search for wiring diagrams if you haven't already and make sure everything is wired correctly.

[dbc28092]

Thanks for the suggestions.  I took the reman alternator back to AZ and had them test it.  It tested good.

While I had the alternator off, I put my multimeter to the wire going to the battery.  I showed 12v coming from the battery so I would think the wire is good.

I can't understand how my original alternator tested bad and the reman alternator tests good but I'm still having the same problem.  A coincidence that I had a bad alternator AND another problem?  Almost feels like a scam. 

With the truck running, I put my multimeter directly to the post on the alternator where the battery wire connects.  I only get 12v and I suspect that reading is coming from the battery.

[VileZambonie]

SI or CS alternator? What do you measure at terminal 1? Terminal 2? Bat terminal? on the alternator???

[dbc28092]

According to my Chilton's manual, it is a SI.  I have only checked the voltage at the BAT terminal on the alternator and the posts on the batteries.  I get 11-12 volts.  I have not checked at terminal 1 or 2 on the alternator.  Do I unplug the connector at terminal 1-2 to check with the multimeter?

[bake74]

  While I had the alternator off, I put my multimeter to the wire going to the battery.  I showed 12v coming from the battery so I would think the wire is good.

     You tested a unladen circuit.  Meaning you only tested the wire without any actual amps going through it.  A good example would be a fuse. 
     A fuse can test ok when checked with a ohm meter by itself, but put it in a circuit and apply power running through the fuse, and then check the fuse for power after the fuse,  and you can get none.  Just because something test ok when by itself or outside a circuit does not mean it will test ok again after power and a complete circuit has been applied.

[VileZambonie]

     A fuse can test ok when checked with a ohm meter by itself, but put it in a circuit and apply power running through the fuse, and then check the fuse for power after the fuse,  and you can get none. 

You lost me....

[Irish_Alley]

personally never had it happen with a fuse. but some run into this problem with starter cables.
but put the tester on number 1 post on the alt it should read  1V+
Number 2 post and ground should read 12V
this is with the connector plugged in

[bake74]

     A fuse can test ok when checked with a ohm meter by itself, but put it in a circuit and apply power running through the fuse, and then check the fuse for power after the fuse,  and you can get none. 

You lost me....

      I run into this all the time on my job.  No power will get through the fuse but will check out ok if you take it off and do a continuity check on it.
      At the front of the fuse you will have power between this point and ground (or the other leg if other than 12v), and after fuse no power, even though it passed a continuity check.
      I still find it amazing, but it does happen.
      The best I can make an example is when you have bi-metal strips like in a house thermostat that are suppose to separate when they heat up.

[Irish_Alley]

kind of ran into a similar problem like this but it was on ac. our pipe bender would turn on (the pump) but it wouldnt get signal from the pedals to work. the pedals are 110 and the bender pump is 220. friends brother in-law was a nuke in the navy. he couldn’t figure it out spent a hour or two testing the pedals, sometimes it would work other times no.

they said it was the pump itself. this didnt seam right to me so i study it and after testing volts all around we took the relays out and tested them by themselves and they would work by just plugging them into the wall. Cleaned them up and put it all back together and still nothing. then i started to think about it the pump is 220 so it doesn’t need a ground the pedals are 110 so they need a ground even though we got 110 to the pedals there was resistance somewhere in the lines to prevent it from working. took the relay back out and jumped it directly to the junction box on the side of the pipe bender still nothing. so figured it was the 220 extension cord. took apart the male plug and the ground wire was at one point wires up but the guy who did it didnt tight the main wire clamp down and it pulled out the ground. weird part was it wasnt connected but we got 110 from both legs if we grounded it. wired it back up and gave the nuke a wink cause he just knew it was the pump