Alternator/Charging Problem- 1998 GMC Jimmy 4.3

I have a problem with the alternator not turning on after starting the vehicle. After I start the vehicle the battery gauge stays at around 12 volts and the Battery/Charging idiot light stays on. At times it takes anywhere from 15 seconds to 20 plus minutes for the alternator to kick in and the battery gauge shoots up to around 14 volts and the idiot light shuts off. This problem never happens in freezing temperatures and never on morning startups, but always happens on a hot summer day after starting and stopping the vehicle throughout the day. I have noticed that while the problem exists, and the idiot light is on, if I connect a battery charger to the battery and put it on the 200 amp setting the alternator immediately kicks in and the idiot light shuts off. It seems light like there is a communication problem that is not relaying a signal to the alternator/regulator to turn on. I have installed a new/remanufactured alternator and purchased a new battery, but the problem still exists. I have had this problem for years and it seems like just recently it has become worse and is starting to leave me stranded as at times the alternator will not kick in and the battery drains right out. I am wondering if the computer might be defective or I was also informed that the cluster may be defective as the battery gauge may not be sending a signal to the computer. Any advice would be greatly appreciated.

This article may help with your situation. The cs series alternator depend on rotational speed to excite the regulator. Some will seem lazy and need additional rpm's to charge. Low initial voltage hampers this action as well.
Hope this helps.




Delco Remy CS130 Series Service Manual

For Delco Remy CS130 and CS121 Series Alternators, Page 2

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OPERATING PRINCIPLES

Unlike other charging systems which have three wires connected to the alternator, the CS-121 and CS-130 may be used with only two wires connected to the alternator. The output wire to the battery positive, and an "L" terminal wire connected to the charge indicator bulb, or to the resistor, or to both. A basic wiring circuit is shown (Figure 3).
The charge indicator works in much the same way as on other charging systems-the indicator lights when the switch is closed, and then goes out when the engine is running. If the charge indicator is on with the engine running a charging system defect is indicated. For all kinds of defects, the indicator will glow at full brilliance. A new feature of this regulator is that it will cause the charge indicator to be on with the engine running if the system voltage is too high or too low. The regulator is temperature-compensated; that is, it's voltage setting varies with temperature.

As in other alternators, the regulator limits the system voltage by controlling the rotor field current. Unlike other regulators, this regulator switches the field current on and off at a fixed frequency of about 400 cycles per second. By varying the on-off time, the correct average field current for proper system voltage control is obtained. At high speeds, the on-time may be 10% and the off- time 90%. At low speeds with high electrical loads the on-off time may be 90% and 10% respectively.
The use of the "P", "F", and "S" terminals is optional. The "P" terminal is connected to the stator, and may be connected externally to a tachometer or other device. The "F" terminal is connected internally to field positive, and may be used as a fault indicator. The "S" terminal may be connected externally to a voltage, such as battery voltage, to sense the voltage to be controlled. For complete circuit, reference must be made to the vehicle manufacturer's wiring diagrams.

Where the regulator is identified with an "I" marking on the regulator case, the circuit in Figure 3A applies. In this circuit, both the "L" and "I" terminals serve to turn on the regulator and allow field current to flow when the switch is closed. The "I" terminal may be connected directly to the switch, or through a resistor. Both are illustrated. The "I" circuit may be used with or without the "L" circuit that is, with or without anything connected to the "L" circuit. The vehicle circuit can be identified, Figure 3 or Figure 3A, by observing the terminal marking on the regulator, which will be either an "F" (Figure 3) or "I" (Figure 3A).
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There are only two wires attached to the alternator. The 14 gauge brown wire at the regulator is good or the dash light wouldn't come on. Follow the 10 guage red wire from the back of the alternator to the fusible link**, to the 175 amp MaxiFuse under the battery tray. Check all connections; make sure they're clean, tight, and free of corrosion. Must have battery voltage on the red wire on the alternator at all times.

** Fusible link attaches to the un-fused side of the MaxiFuse

If you want to have the alternator to charge immeadiately upon start up, you may attach a ignition feed wire to the "s terminal on the regulator. Test this first before running wires etc.
I had several issues with this alternators big bother (21 SI). They seemed very lazy at start up so we ran an ignition controlled wire to them and had full charge right from the get go.

Thank you all for the suggestions. I will try them out and post back.

If you want to have the alternator to charge immeadiately upon start up, you may attach a ignition feed wire to the "s terminal on the regulator. Test this first before running wires etc.
I had several issues with this alternators big bother (21 SI). They seemed very lazy at start up so we ran an ignition controlled wire to them and had full charge right from the get go.

Thanks Toddman. Just to clarify, I would run a 12V ignition controlled power wire to the "s" terminal on the regulator? Or straight from the battery? Also, is a fuse recommended between the two points? And lastly, am I taking any risks by doing this, as in affecting the operation of the computer? Thanks.

First I would hook a volt amp meter to the battery. I would then make a fused test lead from the battery, start the vehicle and apply the fused test lead to the s-terminal on the alternator and see how the alternator reacts. If this proceedure makes the alternator excite and charge immediately without over charging, then I would make a fused Ignition supplied wire for the permanent repair.

If this does not satisfy the problem, I would start looking for a problem such as a broken or fusible link. This could be tested by disconnecting the main wire from the alternator and make another test lead connected from the alt to the battery, and check with a volt meter.

My suspicions are that the resistor that controls the voltage excitement is either bad or a bad fusible link is bad.

Do some testing and see what happens, Perhaps by then someone with a similar problem may weigh in here.

The 10ga red wire on the back of the alternator must show battery voltage at all times. The 14ga brown wire on the side of the alternator must show battery voltage with the ignition in the START and RUN positions. If both wires are showing proper voltage and the alternator does not charge, the alternator is faulty. If the brown wire does not show battery voltage, check the fuse and/or repair the open circuit. If the red wire does not show battery voltage, follow the wire back to the fusible link and repair the open circuit.

Thanks Old Master,

Apperently there seems to be an open circuit or perhaps another bad alternator. I know that these alternators a temperature sensitive with regards to the regulator. The new reman alt. may be defective as well. Your straight forward test should be the answer.

The 10ga red wire on the back of the alternator must show battery voltage at all times. The 14ga brown wire on the side of the alternator must show battery voltage with the ignition in the START and RUN positions. If both wires are showing proper voltage and the alternator does not charge, the alternator is faulty. If the brown wire does not show battery voltage, check the fuse and/or repair the open circuit. If the red wire does not show battery voltage, follow the wire back to the fusible link and repair the open circuit.

Thanks Old Master,

But, what do mean by the "14ga brown wire on the side of the alternator". I have the 10ga red wire on the back of the alternator and a thin red wire on the side going to the "L" terminal. Thanks for your help.

The thin red wire on the side must show battery voltage when the ignition is in the START and RUN positions.

The thin red wire on the side must show battery voltage when the ignition is in the START and RUN positions.

Thanks again Old Master,

Please bare with me as auto electric is not my specialty. Okay, the 10ga red wire on the back of the alternator always shows approx. 12 volts. I disconnected the connector on the side of the alternator and the 14ga red wire has approx. 12 volts in the start and run positions(once again, the connector is disconnected while checking voltage), these readings were consistent regardless if the fault was present or not. So based on this info, would you say my 2nd alternator is faulty as well? Thanks.

Good job! Yes, the alternator is faulty. Some of the chain type auto parts stores have "off the car" alternator testers that are quite expensive and the employees think the results are "Gospel". That's not the case, along with Chilton & Haynes repair manuals, don't trust them. They're right 50% of the time. The problem is, you don't know what 50% you're dealing with ;) Get another alternator on there and post back your results.

I will be picking up a new AC Delco alternator tomorrow AM. The last 2 alternators were made by Wilson Auto Electric, so its time to try a different brand. I will post the results after the install...thanks again.

Problem corrected. I installed a brand new bosch (not rebuilt) alternator about 3 weeks ago and all is good. Who would have figured that a 3rd alternator swap would do it. Thanks guys for your help, I can finally stop pulling my hair out.

Good quality parts save a lot of time, money, and headaches. Thanks for posting back with the fix.

I have a 2000 blazer--changed alternator after voltage reading dropped to battery and dash meter dropped to 12 v. got a reman and now the voltage gage on the das is drifting a notch ,then higher--I carry a cigarette lighter adapter w/a plug on the end so I canmonito the voltage w/avolt meter while driving, pull over of course--seems to stay close to 14 volts.Is this alternator faulty too? has a black plastic cover that came attached to the back, is it supposed to be on it? old one had one--

my blazer's 2000 volt meter is drifting a notch downwards aftr replacing w/a reman. I us a cigarette lighter plug to monitor the voltage. it never drops below 14v fully loaded, what it it, a faulty in dash regulator?