PCM or Alternator? - JeepForum.com
 
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post #1 of 9 Old 04-23-2017, 09:57 PM Thread Starter
Jeep6488
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PCM or Alternator?

I have a 1998 ZJ Grand Cherokee Limited with the 5.9L v8. It started acting like the voltage regulator is out. The voltage hovers around 13 volts but drops when an accessory (say the turn signal or a/c) is turned on and will slowly rise again. I have looked all over the internet and most places say that it is probably the voltage regulator. However, upon further research (and here is where it gets fun), I have learned that the voltage regulator is part of the PCM and is known as an Electronic Voltage Regulator (or EVR/EVR circuit/EVR circuitry). had the Jeep checked an it did come back as the voltage regulator malfunctioning BUT, not a single OBD II trouble code to be spoken of. All this being said, is there a specific trouble code the computer will read if the EVR is bad? and How do I tell if it is the EVR (in the PCM) or if it is just the alternator being the stinker. This whole situation has me very frustrated so any help is greatly appreciated. thanks all.

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post #2 of 9 Old 04-24-2017, 11:00 AM
kg6mov
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With EVR failure we usually see no code, no charge. I would put my money on the alt over the PCM.

Have you cleaned all the grounds?


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post #3 of 9 Old 04-24-2017, 02:19 PM
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It's the alternator. Look into the Durango 160 amp alternator upgrade.
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post #4 of 9 Old 04-24-2017, 02:30 PM
wingless
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Welcome to the forum.

+1 on checking for clean and tight connections. Ensure the battery negative is disconnected prior to working on the wiring.

The alternator is "easy" to test. The small wires on the rear are the field connections. One is at battery voltage. The other is controlled by the PCM, lower voltage = more output.

It is possible to ground the PCM field connection on the alternator to force maximum output, like when doing FSM alternator testing. Grounding that PCM output will create an error code that can be cleared once testing is completed.

This topic shows my alternator testing per the FSM.

The normal 90A or 135A alternators are fine, unless an ear-bleeding stereo amp or other abnormally high current load is part of expected vehicle operation.


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post #5 of 9 Old 04-24-2017, 02:49 PM
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Have your battery tested with a load tester if its got caps check the acid level , at the same time use a hydrometer and check the acid specific gravity. clean the post as well, and check grounds frame and engine for corrosion.
you can get a load tester at harbor freight under $20. and hydrometer $2.
or take to auto store they will check it for free.
Alternator only work if the battery is in good shape.

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post #6 of 9 Old 04-24-2017, 02:59 PM
kg6mov
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Quote:
Originally Posted by wingless View Post
The normal 90A or 135A alternators are fine, unless an ear-bleeding stereo amp or other abnormally high current load is part of expected vehicle operation.
Don't install a 90A on a 5.9, the draw from the efan is too much. I wouldn't even do a 135A.


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1984 F250, 460 BB, T19, work truck/future tow pig
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Quote:
Originally Posted by Texas ZJ1 View Post
I heard someone yell "mall crawler" from the back porch. I'll go see who said that. Be right back.
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post #7 of 9 Old 04-24-2017, 03:28 PM
PolkaPower
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Quote:
Originally Posted by kg6mov View Post

Don't install a 90A on a 5.9, the draw from the efan is too much. I wouldn't even do a 135A.
Yeah go stock or higher for the 5.9. You can exchange yours for a rebuilt one. I think I paid about 110 for a rebuilt stock 150 with core exchange.
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post #8 of 9 Old 04-24-2017, 04:24 PM
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Quote:
Originally Posted by hotvak123
Have your battery tested with a load tester if its got caps check the acid level , at the same time use a hydrometer and check the acid specific gravity. clean the post as well, and check grounds frame and engine for corrosion. you can get a load tester at harbor freight under $20. and hydrometer $2. or take to auto store they will check it for free. Alternator only work if the battery is in good shape.
Totally agree!!!


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post #9 of 9 Old 04-25-2017, 12:21 AM
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OBD I/II won't tell you if the voltage regulator has gone bad, it will only tell you if the charging voltage is too high or too low.

Check your belt tension first to ensure the alternator pulley is properly driven by the belt.

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