I have an 85 and the car is not holding any type of charge. My voltage readout has always been low, I took it in and they said it was reading at 12-13v and that the car was running off the battery than the alternator. The battery is brand new, a month old, the cables all look fine, I just rebuilt the alternator a week ago. I charged the battery after I put the alternator back in and the voltage read 11.4-12.4 when I had it on accessories and when started and running the voltage read a steady 14+v which to my understanding is where it should be. I drove my vehicle for an afternoon and figured the charge would have helped the battery somewhat, each morning the voltage would read 9.7-10.4v when I'd turn the key. At that voltage I get nothing, no cranking. I am very confused now on what the problem could be. I got an engine code after I put in the new alternator, code read 15 and according to my books that is the coolant temp circuit/low temp.

If someone as any idea of what the problem could be I'd love to hear it. Its frustrating at this point and I'd hate to go into the winter season knowing my car won't run when it comes out.

The battery was tested after the alternator was put back in and I was told everything looked fine.

Jason

 

If you are showing 14 V while running, the charging system is fine. If you stop the car after driving, will it restart?

If the battery goes down overnight, you either have a parasitic drain or a bad battery. New batteries go bad.

 

Well when I go to start it up again the first time it cranks a bit and won't go over so I wait a second and shut off the radio and then it cranks up. I guess that could mean the battery, I'm just not sure on that since I was told the battery is fine.

 

Could also be the starter or associated wiring. A good battery should not drop lower than 9 V while cranking.

 

I'm going to bump this up, I exchanged the battery and it wasn't indeed holding a charge anymore however the new one is already dipping down which likely means there's a short somewhere and in all honesty I'm not sure how to diagnose something like that.

However before the alternator was rebuilt the only code I've ever gotten was the TPS, and the battery was really fine until I found out the alternator wasn't working. When I put the alternator back in I get a new code, I cleared it just to make sure its a problem and not something from not being hooked up for a while, and it flashes code 15. I'm hoping, just because I don't know where to start if this isn't the problem, a sensor would drain power if its not working properly or if the wires are messed up. So I'm not sure if there's an electrical forum or not but anyone with experience here, some help would be greatly appreciated.

 

An alternator can put out good voltage numbers but low amps. Shops can spin an alternator and tell you it's charging fine but they are just checking voltage, not amperage.

If you suspect a voltage drain. Remove the negative battery cable and put a amperage meter between the cable and battery to find out how much drain there is. Make sure no interior lights are on, including the under-hood light before disconnecting the battery. Post back what the amp drain was. We can try and help narrow it down for you.

 

Where the diodes replaced, in the alt ??
If you have a code 15, diagnose now. It will run like crap if the coolant temp sensor/wiring/connection is screwed.

 

regarding your code 15, most likely the wire(s) to your coolant temperature sensor has come off or been broken.

Not sure where the sensor is on the 85, but wild guess is driver's side head or thermostat housing or water pump, so check for all three.

regarding battery drain, some typical places to look for drain: car seats, antenna motor, or interior lights staying on because door switches have failed.

BTW, a battery disconnected and fully charged, voltage should read 12.6+, but connected and key on, 10.5-11.5 is normal.

 

The diodes in the alternator can turn on and off at will if they are defective....... and I don't think you ecm will function below about 9 volts if I remember correctly.....I used to pull the positive cable off the battery when it was running while trying to diagnose...if the car kept running it was the battery, if it died it was the alternator.

 

Disconnect the negative battery cable and insert a DC Ammeter (not voltmeter) between it and the negative post on the battery. According to my FSM, the total load should be 14.9 milliamps @ 12.6 vdc when the CCM is asleep with the key out of the ignition.

From FSM pg 6D1-4

Load Name.................................... Milliamps
ECM Memory.................................. 2.5
HVAC Control Head .........................0.2
HVAC Programmer...........................4.8
CCM Asleep (Key Out).....................1.4
Headlamp Door Control Module..........2.1
Generator Output...........................1.1
Chime Module................................0. 8
Radio Control Head.........................0.6
Radio Receiver...............................1 .4
Total................................... .........14.9

If you get a high reading, pull fuses one by one until you find the one that brings it down to normal limits. Then troubleshoot that circuit.

By the way, it's hazardous to your meter attempting to measure current on a motor vehicle, because an un-planned for sudden load (such as opening a door, a remote being activated, etc.) will at least blow the fuse.

Consider purchasing a 1 Ohm power resistor, and install it temporarily (for troubleshooting purposes) between the battery + terminal
and the + lead. Since I=E/R, measuring the voltage drop across the 1 Ohm resistor will allow you to directly read the current being
used by your vehicle. 1mV=1mA.
.

 

Now that is an excellent technique. I will have to remember that one.

 

Courtesy of the United States Navy
Electrician’s Mate Class A School
Great Lakes, IL
Class of 1963

 

Very good ideas, I'm gonna check them all out this afternoon, thanks for the ideas so far guys I hope I can pinpoint it! Wish me luck :-P

Oh yea, the diodes were replaced, I replaced that and the voltage regulator, I was told the rectifier and everything else was just fine. I'm gonna try the fuse idea for sure, that's a really good way to pinpoint that stuff, never would have thought about that one.

 

You don't use a fuse.

 

one thing to remember is that an alternator produces ac/dc current rectified to dc only with the diode trio, while a generator produces dc current only. pulling a cable off a battery while the engine is running is a quick way to overload/spike the diodes in an alternator and cause them to fail - even if you shut the engine off before you reattach the cable. (this IS a great way to test a generator, though). as far as having 14+ volts, that would indicate the alternator is producing power (voltage) but not necessarily current flow (amperage). if you've spiked your diodes, or the trio you put in was defective (diode failure is the most common failure in a GM alternator) you'll be producing ac current (flows positive then negative) and in effect not doing anything except keeping the ignition hot once the engine is running (the flow is 000's of cycles per second). alternator voltage and amperage output can easily be checked at any reputable parts store. pull the alternator and have it bench tested and you'll know for sure. about the only parasitic drains that can take a battery all the way to zero volts are lights and lighters. most motors and control modules will not operate below 6-9 volts. an internal short in the battery will cause a demand for extremely high (16+ volts) from the alternator.

 

Well I'm going to check each area out one at a time but I wanna mention in here that the seats haven't posed any problems thus far, the antenna was replaced and I'm sure thats fine, but when you mentioned the door switches it leaves me asking, what do you mean? My lock buttons have always given me problems, it takes a few tries of pushing it to get it to click and even then the actual bars won't move and most times I have to manually push them to the lock position. I'm wondering about the wiring in there too, I never realized but the weatherstripping on the bottom of the windows is broken apart and I noticed that some nights after it rains that there's a small puddle by the bottom of my door which is why I feel thats my best bet after the mentioned of door switches.

I had the Alternator checked again at the local parts store and they again told me its fine but it was mentioned that they will measure voltage not amperage so by disconnecting the negative battery cable and putting an amp meter to it is that the right way to check that? Also should I have the key on the accessories or not in at all?

 

I'm a little confused with this one, is this something I should try to do? and if so as mentioned, my understanding is it'll blow the diode. If its not something I should do, which from the sound of it I shouldn't, should I double check the diode assuming I could have done something like that while diagnosing other problems or by accidentally doing something while the car was in operation.

 

I had the alternator checked again and now I was told it is not working, I'm searching for ways to test the alternator itself and each of the components but I have no idea how to check the rectifier and diode and I'm assuming like any normal capacitor you'll be able to tell if its good or bad just from looking at it.

 

the "secret" code for remembering the color codes on resistors? Anybody in the Navy with electrical training will *never* forget that one...am I right? :-)

 

Anybody with electrical training anywhere knows that one. I think it goes hand in hand with being one of the few surviving male bastions.