Charging lack of

[KnuckleHead]

For last couple months I have been working on going TBI in my Blazer. I picked up a good running 94 350 TBI with computer and wire harness out of a Suburban. Everything dropped in great even the wire harness. This past weekend I had it up and running ready for a test drive. I was able to go up the street to the store and back with no problems on Friday. Saturday I get in start her up and head to a friends house, I was only there about 15 minutes , go to start the truck....dead battery. Get a jump and get home, turn the truck off then try to restart, again dead battery. My guess was that the alternator was bad so I took the one out of my 94 Chevy 3500 that I know is good. Once it was in I get another jump and let it run for a couple minutes. As I was just getting in the truck to move it it dies and wont start, dead battery again. So my buddy takes me the parts store to test the alts, both are good to go.

So I did some research today and got myself and voltmeter. When I check the battery it reads 11.94, will not turn the motor over. So I jump it with my other truck, as I let it idle I put the meter on the battery, you can watch the volts just drop till the truck dies. So I start thinking that maybe the wire from the alt to the battery might be bad and change it, once again the truck starts with a jump and loses power still till it dies.

So I'm kinda at a loss here ans could use some help. Anyone have any ideas thoughts or the solution to this?


Thanks in advance......

[Chris]

This may be too easy an answer Happy but have you tried a differet battery?

[KnuckleHead]

Opps for to mention that..... I did also take the battery out of my other truck with no change....it still dies. And the alt that I thought was dead is now in my 3500 and working great, so the parts store was right, it's good.

[Brad]

Did you check all the grounding contacts in the charging system? Perform a voltage drop test?

[KnuckleHead]

I checked ground to block, block to body and battery to body. I moved the battery to body and block to body with no change. It's almost like there something not telling the alt to charge.

[Hypoid]

It's almost like there something not telling the alt to charge.I think you are on track, Happy. You need to study up on the donor's charging system.

[Popsgarage]

Does your truck have a CEL (Check Engine Light) or alternator/battery idiot light? If it does, does it work and has it always worked and recently stopped working? If the CEL/alternator/battery light burns out the alternator won't charge correctly. Check out the Diode failure section especially the one regarding the Charge indicator light. This light is used as one of the diodes, and if it burns out, the alternator won't charge correctly.

http://www.aa1car.com/library/charging_checks.htm

Check post 5 and 6.

http://www.fullsizechevy.com/forum/general-discussion/technical-maintenance/476777-1987-chevy-truck-charging-problems.html

[Brad]

Voltage drop test will find where your losing the charge.

Basic voltage drop test with DVOM (I tried finding a video on YouTube but they were all terrible)
i use this test all the time.

-Connect negative or common to negative terminal on the battery.
-Connect positive lead to the positive terminal on the battery.

What is your voltage reading?

-Leaving the negative on the battery move the positive lead to each connecting point all the way to the alternator taking a reading at every stop. You should see full charging voltage around 14v along the way. You can also leave the positive lead on the positive terminal on the battery and backtrack your ground connections. You may also track any power connections forward of the battery (ie any connections directly connected to the battery to see if a consumer is sucking down all the charging voltage from the battery)

Result: if you are losing voltage at any point you can start to find where your charging problem exists (also known as voltage drop).

I would also run these tests with someone revving the engine if you see no drop at idle as you may have a load based drop.

Remember, resistance tests will not show you a charging problem. One strand of wire will show a good circuit.

if this is confusing let me know, I will be more than Happy to come help you out! ( no pun intended) :D

[KnuckleHead]

So as I am going from carb to tbi I thought I would just make a custom dash with aftermarket gauges and all. After reading Pops replay it got me thinking. When I got the jump at my friends house I did plug the stock 94 gauge cluster in and the volts read 14.0. As it was just hanging there the truck never had a problem but I had to disconnect it to drive home and bam dead battery...???? So after work today I plugged it back in and what do you know it was working, the truck stayed running. I tested the battery with the voltmeter and it was up around 13.90s. I'm guessing this is the resister/diode that is used for the charging that is connected to the battery light..? Looks like you hit that one right on the head there POPS..... thank you

So here's another question someone might be able to help with...... how can I bypass this? What will I have to do when I get my new voltage gauge?

[KnuckleHead]

Brad....
Thank you for the write up on the testing, I'm sure that will come in handy one day. And thank you for offering to come lend a hand. I think one I get past this I will be good to go and I can really get out there on the road for testing. Looks like I am going to have to find a way to use the 94 gauge cluster for now till I get the rest of my gauges though.

[Popsgarage]

connected to the battery light..?

Exactly right! It simply takes the place of a resistor or diode, can't remember which. To bypass you need to place a diode inline. I can't seem to find the original write-up on this in my bookmarks that told you what to do. I'll keep looking. Or, if you're installing a custom dash, you could simply install a light on the dash.