Here's the deal.... The battery does not seem to be charging. The battery holds a charge and tests good. If I charge the battery with a charger, it starts and runs fine (for a few times until the battery runs down). The lights and A/C blower sound like they are running at normal speed and there doesn't seem to be any sign of a short. I replaced the alternator, but the problem continues.

I have tested the charging system according to the shop manual up to the point of putting a load on the alternator. I have tried the full field test and output voltage jumps to 18v like it is supposed to. I have a DC amp meter on the way, so I'll try that in a few days.

Question: the manual shows the 4-wire plug to have an IGN wire (12v when key is on), the "L" wire which turns on the battery check light when grounded. Then there are 2 wires from the ECU "R" and "F". I cannot find anything describing the signals or function of these two wires.

I did find a reference to a GM Delco alternator with the same connection names. It was attached to a Briggs and Stratton to make a generator and just had IGN, R, and F all connected to 12v and the L connected to ground.

Can anyone shed light on the R and F wires?

 

I looked up the wiring again and wanted to clarify the wires.

B- Heavy guage charging wire to the battery.

On the 4wire connector:
L - The Alternator grounds this wire (sinks) in order to turn on the "Check Battery" light.
IGN - 12v line that comes on when the ignition is in RUN position.

FR - ? Goes to ECM
C - ? Goes to ECM

I have seen suggestions that FR is a "Field Reference" and is just an output signal back to the ECM to correct for voltage fluctuations.

I also know that the voltage output can be modified some by the ECM. Under certain conditions such as highway driving with low electrical usage, the output can be dropped from 14.5v to 12.5v. I strongly suspect the "C" wire to be used for this as the manual diagram seems to associate this wire with an output from the ELD, although they are not connected.

 

Check to see if your battery is good. It might look ok, and might hold a slight charge, but in fact be a dead battery. Have someone hold a Voltmeter to the Battery, and then try starting the car. The battery voltage should not drop below 9.6v at any time. Best way is to take out the ecu fuse so that the car will not start while cranking for 5 sec.

 

I got my DC amp meter in today. The alt seems to be working properly. It charges at 35-40 amps and goes to about 68amps with A/C and lights on. I am now pretty sure that this is a battery problem. I originally thought this, but I have had the battery tested four times over the course of three months while troubleshooting and the current battery is only about 18 months old.

Anyway - I am 95% sure that a new battery will fix the problem.

 

Did you even read my comment on your problem? Or did you completely skip wat I said, and kept doing your own thing?

 

Sorry - Thank you for the post. I posted back on my discussion before I read what you said.

In response, yes, the battery is rather dead. I can charge the battery with a charger and it will start fine for a few times. You can tell when the battery gets really low because the starter solenoid will drop out every time a compression stroke hits. In retrospect, even after a charge it does seem weak, but I had the battery tested several times. They said it tested within spec and that the battery was big enough for the car, but I am pretty certain that it is not OK. Since their test (Walmart) says the battery is good, they will not do anything on the warranty.

Thank you for the post. :D

 

If the battery is bad, you can charge it, and start it a couple times but it will die again. We had the same problem in my electrical class couple of weeks ago. It would charge ok, and would start fine once or twice, then start going dead.Like I said, have someone try starting the car while you hold a voltmeter across the battery and see how far the batt drops while cranking the engine. It shouldnt drop below 9.6v at any time.

 

Issue solved - Walmart SUCKS. tester says battery is good, so they won't replace the 18mo old battery. New battery works like a champ..... Although I did go for a bigger battery. The new one is 850 amps while the old one was 625.