1988 Suburban, battery won't charge

[unixfmike]

I've replaced the battery, battery cables, and alternator. I opened up the wire covers and looked at the wires. There is no bare or broken spots, all the wires look good. The suburban will turn over and run just fine, but I only have 2-3 hours of actual run time because the battery (new or old) slowly dies. The voltage reading at the back of the alternator is 12.43 volts with the engine running, and 12.44 volts at the battery with a fresh charge on the battery. With the engine running, the voltage slowly goes down over time and eventually gets low enough that the engine stops. I took the alternator to the local parts house and it checks out good, it passes all tests.

I know the voltage output at the back of the alternator with the engine running should be between 13-15 volts, but it is not. The voltage is normally .01 - .02 volts below the voltage at the battery There is good tension on the belt, and the alternator is turning as expected. Does anyone know of anything else I can check before taking this to a mechanic and have him tell me it's a 5 dollar part and 200 bucks for labor?

--mikew
fort sill, ok

P.S. It's getting kind of old having to carry a spare battery and charge both of my batteries externally every couple of days.

[unixfmike]

I tried removing the plug from the built in voltage regulator at the back of the alternator. The engine will still start and all the accesories still work. With the voltage regulator connected or disconnected the vehicle performance is still the same. The only problem is it still will not charge and continues to put out 12.41 volts at the back of the alternator and 12.42 at the battery. This shows me the battery is slowly dieing through my time of testing, and the alternator is still not charging.

Based on a schematic and wire colors I can see I need to troubleshoot a few things. Due to money constraints I don't want to go buy a bag of parts and replace everything. By simple process of elimination I can tell that the pink/blk wire going to the distributor and the ignition coil allows the engine to run, so those two big components can't be bad since the engine still runs.

Does any one know ways to test the following parts without buying new ones?

Air controller
Vehicle speed sensor buffer
Air diverter valve
Electronic Vacuum regulator valve
Air select Valve
Air switch
Electronic Vacuum regulator solenoid

--mikew
fort sill, ok

P.S. There is a also new Electronic Controll Module, Fuel Pump Relay, and Fuel Pump in the truck if that's of any help to anyone.

[jdl]

Do you have excite voltage to the alternator? What type alternator? I don't have a good diagram for your alternator circuits.

Do you have a charge lite on the dash, does it work, key on, no crank?

[unixfmike]

The alternator is a valucraft 105amp remanufactured factory unit I bought from Autozone just a week ago. The voltage at the alternator is consistently .01 volts lower than the battery. After having let it sit for a while and banging on my head with a rusty wrench I went out and checked the voltage again. The voltage is now 12.51 volts at the battery and 12.50 at the alternator.

I don't have a charge light on the dash. The suburban still runs. I can turn on accessories, lights, radio, etc. If I try to start the suburban it fires right up. My only problem is after 2 or 3 hours of actual run time (2 with lights/AC on, 3 with lights off/AC off), the battery charge is so low the suburban will stop running and not have enough juice to start again. That's when I have to take my spare battery and perform a battery swap.

This is extremely frustrating knowing that it will run fine right now, and on Monday or Tuesday I will be swapping out the battery.

--mikew
fort sill, ok

[jdl]

If you have a standard replacement alternator, it won't charge without the excite voltage.Yes, the aftermarket has a one wire self-exciting alternator, I don't believe you have that. If it has the standard L terminal, with the key on, that wire should be hot, if it isn't, the alternator won't charge.

You can go to alternatorparts.com scroll down to alternator repair instructions, then click on the cs 130 link and read the info. I'm sure they can explain it better than I. goodluck

[unixfmike]

As I stated earlier today "12.51 volts at the battery and 12.50 at the alternator" was my last check of the electronics before I filled the AC and the compressor kicked in. After my last round of tests and checks today, I decided to go ahead and fill the AC with new refridgerant since I had it in my posession and the hood was open. Once I started filling the AC I did notice the compressor was kicking in and the engine idle speed did increase. Blah Blah Blah. I did not check the voltage anywhere before I closed the hood. I just know that I checked the last reading with the engine idling immediately after start up. After having the suburban idling for 15-20 minutes with the front and rear AC blowers running, there should have been a significant drop in voltage.

I read the information on a self exciting alternator at http://www.alternatorparts.com/what_...alternator.htm which is next to the link you suggested. It has the statement "Typically you start the vehicle, rev the motor slightly then alternator starts charging." I was testing prior to engine speed/RPM increasing so I would have seen no improvement all day. I just went out and checked my voltage to the battery at 12.73 volts, which is an improvement on the 12.44volts I started the day with. With the key in the on position the voltage to the L shaped connected was at 12.49volts, and I believe that was the one wire you said should be hot. I don't have the ability to check the same wire for an increase in voltage due to lack of hands/foot for holding a multimeter,connector, ground, and reving the engine.

Overall I see an increase in voltage from start of day untill the end of day after using accessories. Talk about learning something new today.

--mikew
fort sill, ok

[Borguy]

Do you have a battery charge light when the ignition key is "on" before you crank it?
The power to excite the alternator goes through this bulb, so if the bulb is broken, the alternator won't excite and so it won't start charging.

[jdl]

Forget the one wire alternator, I don't believe you have that, sorry I brought it up. The other info on that site should be applicable to your alternator.

Do you have a small multi-wire connector at the alternator, how many wires? My info shows, one of those wires should be brown, my info shows that wire should go to the charge indicator. Key on engine off, there should be some voltage on that circuit. If there is nothing there, you need to check the circuit. Like I said before, I'm looking at a cheap diagram.

[unixfmike]

The plug going into the voltage regulator has 2 wires in it. One wire is brown, and the other is pink w/black stripe. The pink w/black stripe normally has close to the same voltage as the battery. As for the battery charge light I have never noticed one in the last year of owning the vehicle, I never had a need to look as everything ran quite well.

I know I have voltage with the key in the on position on the pink/black wire, and nothing on the brown wire. I would check it now, but unfortunately it is sitting at work in the parking lot with a dead battery, again.

--mikew
Fort Sill, OK

[unixfmike]

So after replacing the battery (again) with a freshly charged battery, the battery was dead in just 2 miles. I have a tendency to believe there is an open circuit somewhere. I love being stranded at the side of the road. Thank god the Army provided me some good boots and good enough physical conditioning to carry my battery the other 2.5 miles to my home.

I'm about frustrated with this suburban now.

--mikew
fort sill, ok

[unixfmike]

Is there any possible way to bypass this "excite wire" setup so that once the engine is running the alternator is charging the battery? I drive at very slow speed (normally 20-25mph) at low engine RPM due to local speed limits going to and coming home from work. Only on weekends do I ever get up over 40mph and recently that has only been once every 2-3 weekends.

--mikew
fort sill, ok

[unixfmike]

I just took apart the dash looking for any bad bulbs, none were bad. All the lights light up. As for indicator lights, from left to right I have "Check Engine", "Fasten Seatbelt", and "Brake". All of the bulbs are good. After putting in a charged battery, I can see that the "Check Engine" light does not turn on during startup, should it? I did notice that the temperature gauge is not functioning either. Is the temp sensor wired into the charging circuit by chance?

--mikew
fort sill, ok

[777stickman]

The pink/black wire is the "exciter" voltage from the ign switch. As long as you have batt voltage to that wire with the ign switch on then that circuit is good. The brown wire goes to the instrument panel warning light. But you say that there isn't one that you have seen. So do you have a volt gauge or is the "alt" warning light not working?

If you do have the light system, then I'm inclined to agree with "Borguy" that the Alt needs to see a ground thru that warning light to "excite" the Alt.

The Alt will not charge the batt thru the internal regulator without the 12v "excite" signal or a ground signal (which very well may come thru the warning light).

Another possibility could be the "fusible link" between the Alt and Battery. Follow the red wire from the Alt to probably a junction block. If any part of that wire looks fried, burnt or toasted the "fusible link" needs to be replaced.

[aztecf]

You may have a bad ground between the alternator and the battery. An easy way to test this is to take a pair of jumper cables, hook one black to the battery negative and clamp the other side black to the alternator housing

Jeff

[777stickman]

Originally Posted by unixfmike

I just took apart the dash looking for any bad bulbs, none were bad. All the lights light up. As for indicator lights, from left to right I have "Check Engine", "Fasten Seatbelt", and "Brake". All of the bulbs are good. After putting in a charged battery, I can see that the "Check Engine" light does not turn on during startup, should it? I did notice that the temperature gauge is not functioning either. Is the temp sensor wired into the charging circuit by chance?

--mikew
fort sill, ok

Change the gauges fuse even though it may look good.